fix: support MCP JSON Schema dialects

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Upgraded `socket.io-parser` to `^4.2.7`. [#1542](https://github.com/sourcebot-dev/sourcebot/pull/1542)
 - Upgraded `fast-uri` to `^3.1.5`. [#1541](https://github.com/sourcebot-dev/sourcebot/pull/1541)
 - Upgraded `ip-address` to `^10.4.0`. [#1540](https://github.com/sourcebot-dev/sourcebot/pull/1540)
+- [EE] Fixed Ask MCP connector tools failing to load when their input schemas use JSON Schema 2019-09 or 2020-12. [#1547](https://github.com/sourcebot-dev/sourcebot/pull/1547)
 
 ## [5.1.5] - 2026-07-31
 

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.test.ts

@@ -0,0 +1,150 @@
+import { describe, expect, test } from 'vitest';
+import {
+ compileMcpJsonSchemaValidator,
+ UnsupportedMcpJsonSchemaDialectError,
+ UnsupportedMcpJsonSchemaFeatureError,
+} from './mcpJsonSchemaValidator';
+
+describe('compileMcpJsonSchemaValidator', () => {
+ test('uses draft-07 when it is explicitly declared', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'http://json-schema.org/draft-07/schema#',
+ type: 'array',
+ items: [{ type: 'string' }],
+ additionalItems: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('uses draft 2019-09 for its declared meta-schema', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2019-09/schema',
+ type: 'object',
+ properties: {
+ known: { type: 'string' },
+ },
+ unevaluatedProperties: false,
+ });
+
+ expect(validate({ known: 'value' })).toBe(true);
+ expect(validate({ known: 'value', extra: true })).toBe(false);
+ expect(validate.errors).toEqual(expect.arrayContaining([
+ expect.objectContaining({ keyword: 'unevaluatedProperties' }),
+ ]));
+ });
+
+ test.each([
+ ['when explicitly declared', 'https://json-schema.org/draft/2020-12/schema'],
+ ['by default when omitted', undefined],
+ ])('uses draft 2020-12 %s', (_name, dialect) => {
+ const validate = compileMcpJsonSchemaValidator({
+ ...(dialect ? { $schema: dialect } : {}),
+ type: 'array',
+ prefixItems: [{ type: 'string' }],
+ items: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate([42])).toBe(false);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('preserves all-errors validation and permits unknown keywords', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ type: 'object',
+ required: ['first', 'second'],
+ unknownServerKeyword: true,
+ });
+
+ expect(validate({})).toBe(false);
+ expect(validate.errors?.filter(error => error.keyword === 'required')).toHaveLength(2);
+ });
+
+ test('does not conflict when separate server schemas reuse the same root ID', () => {
+ const first = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'string',
+ });
+ const second = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'number',
+ });
+
+ expect(first('value')).toBe(true);
+ expect(second(42)).toBe(true);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-07/schema#',
+ 'https://json-schema.org/draft/2019-09/schema',
+ 'https://json-schema.org/draft/2020-12/schema',
+ ])('does not let a remote $id remove the %s meta-schema', (dialect) => {
+ const collidingSchema = compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ $id: dialect,
+ type: 'object',
+ });
+
+ expect(collidingSchema({})).toBe(true);
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ type: 'object',
+ })).not.toThrow();
+ });
+
+ test('resolves document-local 2020-12 references after compilation', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2020-12/schema',
+ $defs: {
+ identifier: { type: 'string', minLength: 1 },
+ },
+ type: 'object',
+ properties: {
+ id: { $ref: '#/$defs/identifier' },
+ },
+ required: ['id'],
+ });
+
+ expect(validate({ id: 'issue-id' })).toBe(true);
+ expect(validate({ id: '' })).toBe(false);
+ });
+
+ test('rejects Ajv asynchronous schemas instead of bypassing validation', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $async: true,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaFeatureError);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-04/schema#',
+ 'https://malicious.example/schema?access_token=secret-token',
+ ])('rejects unsupported dialects without echoing the declaration', (declaredDialect) => {
+ let thrown: unknown;
+ try {
+ compileMcpJsonSchemaValidator({
+ $schema: declaredDialect,
+ type: 'object',
+ });
+ } catch (error) {
+ thrown = error;
+ }
+
+ expect(thrown).toBeInstanceOf(UnsupportedMcpJsonSchemaDialectError);
+ expect(thrown).toMatchObject({
+ name: 'UnsupportedMcpJsonSchemaDialectError',
+ reason: 'unsupported_json_schema_dialect',
+ });
+ expect((thrown as Error).message).not.toContain(declaredDialect);
+ expect((thrown as Error).message).not.toContain('secret-token');
+ });
+
+ test('rejects a non-string declared dialect safely', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: 202012,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaDialectError);
+ });
+});

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.ts

@@ -0,0 +1,116 @@
+import Ajv, { type AnySchema, type ErrorObject, type ValidateFunction } from 'ajv';
+import Ajv2019 from 'ajv/dist/2019.js';
+import Ajv2020 from 'ajv/dist/2020.js';
+
+const AJV_OPTIONS = {
+ addUsedSchema: false,
+ allErrors: true,
+ strict: false,
+} as const;
+
+const JSON_SCHEMA_DIALECT = {
+ DRAFT_07: 'draft-07',
+ DRAFT_2019_09: '2019-09',
+ DRAFT_2020_12: '2020-12',
+} as const;
+
+type JsonSchemaDialect = typeof JSON_SCHEMA_DIALECT[keyof typeof JSON_SCHEMA_DIALECT];
+
+const draft07Ajv = new Ajv(AJV_OPTIONS);
+const draft2019Ajv = new Ajv2019(AJV_OPTIONS);
+const draft2020Ajv = new Ajv2020(AJV_OPTIONS);
+
+const DIALECT_BY_META_SCHEMA_URI = new Map<string, JsonSchemaDialect>([
+ ['http://json-schema.org/draft-07/schema', JSON_SCHEMA_DIALECT.DRAFT_07],
+ ['https://json-schema.org/draft/2019-09/schema', JSON_SCHEMA_DIALECT.DRAFT_2019_09],
+ ['https://json-schema.org/draft/2020-12/schema', JSON_SCHEMA_DIALECT.DRAFT_2020_12],
+]);
+
+export class UnsupportedMcpJsonSchemaDialectError extends Error {
+ readonly reason = 'unsupported_json_schema_dialect';
+
+ constructor() {
+ super('MCP tool schema declares an unsupported JSON Schema dialect. Supported dialects are draft-07, 2019-09, and 2020-12.');
+ this.name = 'UnsupportedMcpJsonSchemaDialectError';
+ }
+}
+
+export class UnsupportedMcpJsonSchemaFeatureError extends Error {
+ readonly reason = 'unsupported_json_schema_feature';
+
+ constructor() {
+ super('MCP tool schema uses an unsupported JSON Schema extension.');
+ this.name = 'UnsupportedMcpJsonSchemaFeatureError';
+ }
+}
+
+/**
+ * Compiles an MCP tool schema with the Ajv implementation for its declared
+ * JSON Schema dialect. MCP 2025-11-25 defines 2020-12 as the default when a
+ * schema does not explicitly declare another dialect.
+ */
+export function compileMcpJsonSchemaValidator(schema: unknown): ValidateFunction {
+ rejectAsyncSchema(schema);
+ const dialect = getJsonSchemaDialect(schema);
+
+ switch (dialect) {
+ case JSON_SCHEMA_DIALECT.DRAFT_07:
+ return compileWithAjv(draft07Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2019_09:
+ return compileWithAjv(draft2019Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2020_12:
+ return compileWithAjv(draft2020Ajv, schema);
+ }
+}
+
+export function formatMcpJsonSchemaValidationErrors(
+ errors: ErrorObject[] | null | undefined,
+): string {
+ // Ajv's error representation and formatter are shared across dialects.
+ return draft2020Ajv.errorsText(errors);
+}
+
+function compileWithAjv(
+ ajv: Ajv | Ajv2019 | Ajv2020,
+ schema: unknown,
+): ValidateFunction {
+ // addUsedSchema: false prevents remote root $id values from entering Ajv's
+ // shared schema registry or conflicting across MCP servers.
+ return ajv.compile(schema as AnySchema);
+}
+
+function rejectAsyncSchema(schema: unknown): void {
+ if (
+ typeof schema === 'object'
+ && schema !== null
+ && (schema as Record<string, unknown>).$async === true
+ ) {
+ // $async is an Ajv extension rather than a JSON Schema keyword. The
+ // surrounding AI SDK validation contract is synchronous, so accepting
+ // it would treat a returned Promise as a successful validation.
+ throw new UnsupportedMcpJsonSchemaFeatureError();
+ }
+}
+
+function getJsonSchemaDialect(schema: unknown): JsonSchemaDialect {
+ if (typeof schema !== 'object' || schema === null || !Object.prototype.hasOwnProperty.call(schema, '$schema')) {
+ return JSON_SCHEMA_DIALECT.DRAFT_2020_12;
+ }
+
+ const declaredDialect = (schema as Record<string, unknown>).$schema;
+ if (typeof declaredDialect !== 'string') {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ // An empty URI fragment does not change the selected dialect. Normalizing
+ // it also accepts both forms used by draft-07 schemas in the wild.
+ const normalizedDialect = declaredDialect.endsWith('#')
+ ? declaredDialect.slice(0, -1)
+ : declaredDialect;
+ const dialect = DIALECT_BY_META_SCHEMA_URI.get(normalizedDialect);
+ if (!dialect) {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ return dialect;
+}

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Upgraded `socket.io-parser` to `^4.2.7`. [#1542](https://github.com/sourcebot-dev/sourcebot/pull/1542)
 - Upgraded `fast-uri` to `^3.1.5`. [#1541](https://github.com/sourcebot-dev/sourcebot/pull/1541)
 - Upgraded `ip-address` to `^10.4.0`. [#1540](https://github.com/sourcebot-dev/sourcebot/pull/1540)
+- [EE] Fixed Ask MCP connector tools failing to load when their input schemas use JSON Schema 2019-09 or 2020-12. [#1547](https://github.com/sourcebot-dev/sourcebot/pull/1547)
 
 ## [5.1.5] - 2026-07-31
 

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.test.ts

@@ -0,0 +1,150 @@
+import { describe, expect, test } from 'vitest';
+import {
+ compileMcpJsonSchemaValidator,
+ UnsupportedMcpJsonSchemaDialectError,
+ UnsupportedMcpJsonSchemaFeatureError,
+} from './mcpJsonSchemaValidator';
+
+describe('compileMcpJsonSchemaValidator', () => {
+ test('uses draft-07 when it is explicitly declared', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'http://json-schema.org/draft-07/schema#',
+ type: 'array',
+ items: [{ type: 'string' }],
+ additionalItems: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('uses draft 2019-09 for its declared meta-schema', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2019-09/schema',
+ type: 'object',
+ properties: {
+ known: { type: 'string' },
+ },
+ unevaluatedProperties: false,
+ });
+
+ expect(validate({ known: 'value' })).toBe(true);
+ expect(validate({ known: 'value', extra: true })).toBe(false);
+ expect(validate.errors).toEqual(expect.arrayContaining([
+ expect.objectContaining({ keyword: 'unevaluatedProperties' }),
+ ]));
+ });
+
+ test.each([
+ ['when explicitly declared', 'https://json-schema.org/draft/2020-12/schema'],
+ ['by default when omitted', undefined],
+ ])('uses draft 2020-12 %s', (_name, dialect) => {
+ const validate = compileMcpJsonSchemaValidator({
+ ...(dialect ? { $schema: dialect } : {}),
+ type: 'array',
+ prefixItems: [{ type: 'string' }],
+ items: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate([42])).toBe(false);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('preserves all-errors validation and permits unknown keywords', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ type: 'object',
+ required: ['first', 'second'],
+ unknownServerKeyword: true,
+ });
+
+ expect(validate({})).toBe(false);
+ expect(validate.errors?.filter(error => error.keyword === 'required')).toHaveLength(2);
+ });
+
+ test('does not conflict when separate server schemas reuse the same root ID', () => {
+ const first = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'string',
+ });
+ const second = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'number',
+ });
+
+ expect(first('value')).toBe(true);
+ expect(second(42)).toBe(true);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-07/schema#',
+ 'https://json-schema.org/draft/2019-09/schema',
+ 'https://json-schema.org/draft/2020-12/schema',
+ ])('does not let a remote $id remove the %s meta-schema', (dialect) => {
+ const collidingSchema = compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ $id: dialect,
+ type: 'object',
+ });
+
+ expect(collidingSchema({})).toBe(true);
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ type: 'object',
+ })).not.toThrow();
+ });
+
+ test('resolves document-local 2020-12 references after compilation', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2020-12/schema',
+ $defs: {
+ identifier: { type: 'string', minLength: 1 },
+ },
+ type: 'object',
+ properties: {
+ id: { $ref: '#/$defs/identifier' },
+ },
+ required: ['id'],
+ });
+
+ expect(validate({ id: 'issue-id' })).toBe(true);
+ expect(validate({ id: '' })).toBe(false);
+ });
+
+ test('rejects Ajv asynchronous schemas instead of bypassing validation', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $async: true,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaFeatureError);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-04/schema#',
+ 'https://malicious.example/schema?access_token=secret-token',
+ ])('rejects unsupported dialects without echoing the declaration', (declaredDialect) => {
+ let thrown: unknown;
+ try {
+ compileMcpJsonSchemaValidator({
+ $schema: declaredDialect,
+ type: 'object',
+ });
+ } catch (error) {
+ thrown = error;
+ }
+
+ expect(thrown).toBeInstanceOf(UnsupportedMcpJsonSchemaDialectError);
+ expect(thrown).toMatchObject({
+ name: 'UnsupportedMcpJsonSchemaDialectError',
+ reason: 'unsupported_json_schema_dialect',
+ });
+ expect((thrown as Error).message).not.toContain(declaredDialect);
+ expect((thrown as Error).message).not.toContain('secret-token');
+ });
+
+ test('rejects a non-string declared dialect safely', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: 202012,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaDialectError);
+ });
+});

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.ts

@@ -0,0 +1,116 @@
+import Ajv, { type AnySchema, type ErrorObject, type ValidateFunction } from 'ajv';
+import Ajv2019 from 'ajv/dist/2019.js';
+import Ajv2020 from 'ajv/dist/2020.js';
+
+const AJV_OPTIONS = {
+ addUsedSchema: false,
+ allErrors: true,
+ strict: false,
+} as const;
+
+const JSON_SCHEMA_DIALECT = {
+ DRAFT_07: 'draft-07',
+ DRAFT_2019_09: '2019-09',
+ DRAFT_2020_12: '2020-12',
+} as const;
+
+type JsonSchemaDialect = typeof JSON_SCHEMA_DIALECT[keyof typeof JSON_SCHEMA_DIALECT];
+
+const draft07Ajv = new Ajv(AJV_OPTIONS);
+const draft2019Ajv = new Ajv2019(AJV_OPTIONS);
+const draft2020Ajv = new Ajv2020(AJV_OPTIONS);
+
+const DIALECT_BY_META_SCHEMA_URI = new Map<string, JsonSchemaDialect>([
+ ['http://json-schema.org/draft-07/schema', JSON_SCHEMA_DIALECT.DRAFT_07],
+ ['https://json-schema.org/draft/2019-09/schema', JSON_SCHEMA_DIALECT.DRAFT_2019_09],
+ ['https://json-schema.org/draft/2020-12/schema', JSON_SCHEMA_DIALECT.DRAFT_2020_12],
+]);
+
+export class UnsupportedMcpJsonSchemaDialectError extends Error {
+ readonly reason = 'unsupported_json_schema_dialect';
+
+ constructor() {
+ super('MCP tool schema declares an unsupported JSON Schema dialect. Supported dialects are draft-07, 2019-09, and 2020-12.');
+ this.name = 'UnsupportedMcpJsonSchemaDialectError';
+ }
+}
+
+export class UnsupportedMcpJsonSchemaFeatureError extends Error {
+ readonly reason = 'unsupported_json_schema_feature';
+
+ constructor() {
+ super('MCP tool schema uses an unsupported JSON Schema extension.');
+ this.name = 'UnsupportedMcpJsonSchemaFeatureError';
+ }
+}
+
+/**
+ * Compiles an MCP tool schema with the Ajv implementation for its declared
+ * JSON Schema dialect. MCP 2025-11-25 defines 2020-12 as the default when a
+ * schema does not explicitly declare another dialect.
+ */
+export function compileMcpJsonSchemaValidator(schema: unknown): ValidateFunction {
+ rejectAsyncSchema(schema);
+ const dialect = getJsonSchemaDialect(schema);
+
+ switch (dialect) {
+ case JSON_SCHEMA_DIALECT.DRAFT_07:
+ return compileWithAjv(draft07Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2019_09:
+ return compileWithAjv(draft2019Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2020_12:
+ return compileWithAjv(draft2020Ajv, schema);
+ }
+}
+
+export function formatMcpJsonSchemaValidationErrors(
+ errors: ErrorObject[] | null | undefined,
+): string {
+ // Ajv's error representation and formatter are shared across dialects.
+ return draft2020Ajv.errorsText(errors);
+}
+
+function compileWithAjv(
+ ajv: Ajv | Ajv2019 | Ajv2020,
+ schema: unknown,
+): ValidateFunction {
+ // addUsedSchema: false prevents remote root $id values from entering Ajv's
+ // shared schema registry or conflicting across MCP servers.
+ return ajv.compile(schema as AnySchema);
+}
+
+function rejectAsyncSchema(schema: unknown): void {
+ if (
+ typeof schema === 'object'
+ && schema !== null
+ && (schema as Record<string, unknown>).$async === true
+ ) {
+ // $async is an Ajv extension rather than a JSON Schema keyword. The
+ // surrounding AI SDK validation contract is synchronous, so accepting
+ // it would treat a returned Promise as a successful validation.
+ throw new UnsupportedMcpJsonSchemaFeatureError();
+ }
+}
+
+function getJsonSchemaDialect(schema: unknown): JsonSchemaDialect {
+ if (typeof schema !== 'object' || schema === null || !Object.prototype.hasOwnProperty.call(schema, '$schema')) {
+ return JSON_SCHEMA_DIALECT.DRAFT_2020_12;
+ }
+
+ const declaredDialect = (schema as Record<string, unknown>).$schema;
+ if (typeof declaredDialect !== 'string') {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ // An empty URI fragment does not change the selected dialect. Normalizing
+ // it also accepts both forms used by draft-07 schemas in the wild.
+ const normalizedDialect = declaredDialect.endsWith('#')
+ ? declaredDialect.slice(0, -1)
+ : declaredDialect;
+ const dialect = DIALECT_BY_META_SCHEMA_URI.get(normalizedDialect);
+ if (!dialect) {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ return dialect;
+}

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Upgraded `socket.io-parser` to `^4.2.7`. [#1542](https://github.com/sourcebot-dev/sourcebot/pull/1542)
 - Upgraded `fast-uri` to `^3.1.5`. [#1541](https://github.com/sourcebot-dev/sourcebot/pull/1541)
 - Upgraded `ip-address` to `^10.4.0`. [#1540](https://github.com/sourcebot-dev/sourcebot/pull/1540)
+- [EE] Fixed Ask MCP connector tools failing to load when their input schemas use JSON Schema 2019-09 or 2020-12. [#1547](https://github.com/sourcebot-dev/sourcebot/pull/1547)
 
 ## [5.1.5] - 2026-07-31
 

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.test.ts

@@ -0,0 +1,150 @@
+import { describe, expect, test } from 'vitest';
+import {
+ compileMcpJsonSchemaValidator,
+ UnsupportedMcpJsonSchemaDialectError,
+ UnsupportedMcpJsonSchemaFeatureError,
+} from './mcpJsonSchemaValidator';
+
+describe('compileMcpJsonSchemaValidator', () => {
+ test('uses draft-07 when it is explicitly declared', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'http://json-schema.org/draft-07/schema#',
+ type: 'array',
+ items: [{ type: 'string' }],
+ additionalItems: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('uses draft 2019-09 for its declared meta-schema', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2019-09/schema',
+ type: 'object',
+ properties: {
+ known: { type: 'string' },
+ },
+ unevaluatedProperties: false,
+ });
+
+ expect(validate({ known: 'value' })).toBe(true);
+ expect(validate({ known: 'value', extra: true })).toBe(false);
+ expect(validate.errors).toEqual(expect.arrayContaining([
+ expect.objectContaining({ keyword: 'unevaluatedProperties' }),
+ ]));
+ });
+
+ test.each([
+ ['when explicitly declared', 'https://json-schema.org/draft/2020-12/schema'],
+ ['by default when omitted', undefined],
+ ])('uses draft 2020-12 %s', (_name, dialect) => {
+ const validate = compileMcpJsonSchemaValidator({
+ ...(dialect ? { $schema: dialect } : {}),
+ type: 'array',
+ prefixItems: [{ type: 'string' }],
+ items: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate([42])).toBe(false);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('preserves all-errors validation and permits unknown keywords', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ type: 'object',
+ required: ['first', 'second'],
+ unknownServerKeyword: true,
+ });
+
+ expect(validate({})).toBe(false);
+ expect(validate.errors?.filter(error => error.keyword === 'required')).toHaveLength(2);
+ });
+
+ test('does not conflict when separate server schemas reuse the same root ID', () => {
+ const first = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'string',
+ });
+ const second = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'number',
+ });
+
+ expect(first('value')).toBe(true);
+ expect(second(42)).toBe(true);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-07/schema#',
+ 'https://json-schema.org/draft/2019-09/schema',
+ 'https://json-schema.org/draft/2020-12/schema',
+ ])('does not let a remote $id remove the %s meta-schema', (dialect) => {
+ const collidingSchema = compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ $id: dialect,
+ type: 'object',
+ });
+
+ expect(collidingSchema({})).toBe(true);
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ type: 'object',
+ })).not.toThrow();
+ });
+
+ test('resolves document-local 2020-12 references after compilation', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2020-12/schema',
+ $defs: {
+ identifier: { type: 'string', minLength: 1 },
+ },
+ type: 'object',
+ properties: {
+ id: { $ref: '#/$defs/identifier' },
+ },
+ required: ['id'],
+ });
+
+ expect(validate({ id: 'issue-id' })).toBe(true);
+ expect(validate({ id: '' })).toBe(false);
+ });
+
+ test('rejects Ajv asynchronous schemas instead of bypassing validation', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $async: true,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaFeatureError);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-04/schema#',
+ 'https://malicious.example/schema?access_token=secret-token',
+ ])('rejects unsupported dialects without echoing the declaration', (declaredDialect) => {
+ let thrown: unknown;
+ try {
+ compileMcpJsonSchemaValidator({
+ $schema: declaredDialect,
+ type: 'object',
+ });
+ } catch (error) {
+ thrown = error;
+ }
+
+ expect(thrown).toBeInstanceOf(UnsupportedMcpJsonSchemaDialectError);
+ expect(thrown).toMatchObject({
+ name: 'UnsupportedMcpJsonSchemaDialectError',
+ reason: 'unsupported_json_schema_dialect',
+ });
+ expect((thrown as Error).message).not.toContain(declaredDialect);
+ expect((thrown as Error).message).not.toContain('secret-token');
+ });
+
+ test('rejects a non-string declared dialect safely', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: 202012,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaDialectError);
+ });
+});

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.ts

@@ -0,0 +1,116 @@
+import Ajv, { type AnySchema, type ErrorObject, type ValidateFunction } from 'ajv';
+import Ajv2019 from 'ajv/dist/2019.js';
+import Ajv2020 from 'ajv/dist/2020.js';
+
+const AJV_OPTIONS = {
+ addUsedSchema: false,
+ allErrors: true,
+ strict: false,
+} as const;
+
+const JSON_SCHEMA_DIALECT = {
+ DRAFT_07: 'draft-07',
+ DRAFT_2019_09: '2019-09',
+ DRAFT_2020_12: '2020-12',
+} as const;
+
+type JsonSchemaDialect = typeof JSON_SCHEMA_DIALECT[keyof typeof JSON_SCHEMA_DIALECT];
+
+const draft07Ajv = new Ajv(AJV_OPTIONS);
+const draft2019Ajv = new Ajv2019(AJV_OPTIONS);
+const draft2020Ajv = new Ajv2020(AJV_OPTIONS);
+
+const DIALECT_BY_META_SCHEMA_URI = new Map<string, JsonSchemaDialect>([
+ ['http://json-schema.org/draft-07/schema', JSON_SCHEMA_DIALECT.DRAFT_07],
+ ['https://json-schema.org/draft/2019-09/schema', JSON_SCHEMA_DIALECT.DRAFT_2019_09],
+ ['https://json-schema.org/draft/2020-12/schema', JSON_SCHEMA_DIALECT.DRAFT_2020_12],
+]);
+
+export class UnsupportedMcpJsonSchemaDialectError extends Error {
+ readonly reason = 'unsupported_json_schema_dialect';
+
+ constructor() {
+ super('MCP tool schema declares an unsupported JSON Schema dialect. Supported dialects are draft-07, 2019-09, and 2020-12.');
+ this.name = 'UnsupportedMcpJsonSchemaDialectError';
+ }
+}
+
+export class UnsupportedMcpJsonSchemaFeatureError extends Error {
+ readonly reason = 'unsupported_json_schema_feature';
+
+ constructor() {
+ super('MCP tool schema uses an unsupported JSON Schema extension.');
+ this.name = 'UnsupportedMcpJsonSchemaFeatureError';
+ }
+}
+
+/**
+ * Compiles an MCP tool schema with the Ajv implementation for its declared
+ * JSON Schema dialect. MCP 2025-11-25 defines 2020-12 as the default when a
+ * schema does not explicitly declare another dialect.
+ */
+export function compileMcpJsonSchemaValidator(schema: unknown): ValidateFunction {
+ rejectAsyncSchema(schema);
+ const dialect = getJsonSchemaDialect(schema);
+
+ switch (dialect) {
+ case JSON_SCHEMA_DIALECT.DRAFT_07:
+ return compileWithAjv(draft07Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2019_09:
+ return compileWithAjv(draft2019Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2020_12:
+ return compileWithAjv(draft2020Ajv, schema);
+ }
+}
+
+export function formatMcpJsonSchemaValidationErrors(
+ errors: ErrorObject[] | null | undefined,
+): string {
+ // Ajv's error representation and formatter are shared across dialects.
+ return draft2020Ajv.errorsText(errors);
+}
+
+function compileWithAjv(
+ ajv: Ajv | Ajv2019 | Ajv2020,
+ schema: unknown,
+): ValidateFunction {
+ // addUsedSchema: false prevents remote root $id values from entering Ajv's
+ // shared schema registry or conflicting across MCP servers.
+ return ajv.compile(schema as AnySchema);
+}
+
+function rejectAsyncSchema(schema: unknown): void {
+ if (
+ typeof schema === 'object'
+ && schema !== null
+ && (schema as Record<string, unknown>).$async === true
+ ) {
+ // $async is an Ajv extension rather than a JSON Schema keyword. The
+ // surrounding AI SDK validation contract is synchronous, so accepting
+ // it would treat a returned Promise as a successful validation.
+ throw new UnsupportedMcpJsonSchemaFeatureError();
+ }
+}
+
+function getJsonSchemaDialect(schema: unknown): JsonSchemaDialect {
+ if (typeof schema !== 'object' || schema === null || !Object.prototype.hasOwnProperty.call(schema, '$schema')) {
+ return JSON_SCHEMA_DIALECT.DRAFT_2020_12;
+ }
+
+ const declaredDialect = (schema as Record<string, unknown>).$schema;
+ if (typeof declaredDialect !== 'string') {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ // An empty URI fragment does not change the selected dialect. Normalizing
+ // it also accepts both forms used by draft-07 schemas in the wild.
+ const normalizedDialect = declaredDialect.endsWith('#')
+ ? declaredDialect.slice(0, -1)
+ : declaredDialect;
+ const dialect = DIALECT_BY_META_SCHEMA_URI.get(normalizedDialect);
+ if (!dialect) {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ return dialect;
+}

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Upgraded `socket.io-parser` to `^4.2.7`. [#1542](https://github.com/sourcebot-dev/sourcebot/pull/1542)
 - Upgraded `fast-uri` to `^3.1.5`. [#1541](https://github.com/sourcebot-dev/sourcebot/pull/1541)
 - Upgraded `ip-address` to `^10.4.0`. [#1540](https://github.com/sourcebot-dev/sourcebot/pull/1540)
+- [EE] Fixed Ask MCP connector tools failing to load when their input schemas use JSON Schema 2019-09 or 2020-12. [#1547](https://github.com/sourcebot-dev/sourcebot/pull/1547)
 
 ## [5.1.5] - 2026-07-31
 

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.test.ts

@@ -0,0 +1,150 @@
+import { describe, expect, test } from 'vitest';
+import {
+ compileMcpJsonSchemaValidator,
+ UnsupportedMcpJsonSchemaDialectError,
+ UnsupportedMcpJsonSchemaFeatureError,
+} from './mcpJsonSchemaValidator';
+
+describe('compileMcpJsonSchemaValidator', () => {
+ test('uses draft-07 when it is explicitly declared', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'http://json-schema.org/draft-07/schema#',
+ type: 'array',
+ items: [{ type: 'string' }],
+ additionalItems: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('uses draft 2019-09 for its declared meta-schema', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2019-09/schema',
+ type: 'object',
+ properties: {
+ known: { type: 'string' },
+ },
+ unevaluatedProperties: false,
+ });
+
+ expect(validate({ known: 'value' })).toBe(true);
+ expect(validate({ known: 'value', extra: true })).toBe(false);
+ expect(validate.errors).toEqual(expect.arrayContaining([
+ expect.objectContaining({ keyword: 'unevaluatedProperties' }),
+ ]));
+ });
+
+ test.each([
+ ['when explicitly declared', 'https://json-schema.org/draft/2020-12/schema'],
+ ['by default when omitted', undefined],
+ ])('uses draft 2020-12 %s', (_name, dialect) => {
+ const validate = compileMcpJsonSchemaValidator({
+ ...(dialect ? { $schema: dialect } : {}),
+ type: 'array',
+ prefixItems: [{ type: 'string' }],
+ items: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate([42])).toBe(false);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('preserves all-errors validation and permits unknown keywords', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ type: 'object',
+ required: ['first', 'second'],
+ unknownServerKeyword: true,
+ });
+
+ expect(validate({})).toBe(false);
+ expect(validate.errors?.filter(error => error.keyword === 'required')).toHaveLength(2);
+ });
+
+ test('does not conflict when separate server schemas reuse the same root ID', () => {
+ const first = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'string',
+ });
+ const second = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'number',
+ });
+
+ expect(first('value')).toBe(true);
+ expect(second(42)).toBe(true);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-07/schema#',
+ 'https://json-schema.org/draft/2019-09/schema',
+ 'https://json-schema.org/draft/2020-12/schema',
+ ])('does not let a remote $id remove the %s meta-schema', (dialect) => {
+ const collidingSchema = compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ $id: dialect,
+ type: 'object',
+ });
+
+ expect(collidingSchema({})).toBe(true);
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ type: 'object',
+ })).not.toThrow();
+ });
+
+ test('resolves document-local 2020-12 references after compilation', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2020-12/schema',
+ $defs: {
+ identifier: { type: 'string', minLength: 1 },
+ },
+ type: 'object',
+ properties: {
+ id: { $ref: '#/$defs/identifier' },
+ },
+ required: ['id'],
+ });
+
+ expect(validate({ id: 'issue-id' })).toBe(true);
+ expect(validate({ id: '' })).toBe(false);
+ });
+
+ test('rejects Ajv asynchronous schemas instead of bypassing validation', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $async: true,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaFeatureError);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-04/schema#',
+ 'https://malicious.example/schema?access_token=secret-token',
+ ])('rejects unsupported dialects without echoing the declaration', (declaredDialect) => {
+ let thrown: unknown;
+ try {
+ compileMcpJsonSchemaValidator({
+ $schema: declaredDialect,
+ type: 'object',
+ });
+ } catch (error) {
+ thrown = error;
+ }
+
+ expect(thrown).toBeInstanceOf(UnsupportedMcpJsonSchemaDialectError);
+ expect(thrown).toMatchObject({
+ name: 'UnsupportedMcpJsonSchemaDialectError',
+ reason: 'unsupported_json_schema_dialect',
+ });
+ expect((thrown as Error).message).not.toContain(declaredDialect);
+ expect((thrown as Error).message).not.toContain('secret-token');
+ });
+
+ test('rejects a non-string declared dialect safely', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: 202012,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaDialectError);
+ });
+});

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.ts

@@ -0,0 +1,116 @@
+import Ajv, { type AnySchema, type ErrorObject, type ValidateFunction } from 'ajv';
+import Ajv2019 from 'ajv/dist/2019.js';
+import Ajv2020 from 'ajv/dist/2020.js';
+
+const AJV_OPTIONS = {
+ addUsedSchema: false,
+ allErrors: true,
+ strict: false,
+} as const;
+
+const JSON_SCHEMA_DIALECT = {
+ DRAFT_07: 'draft-07',
+ DRAFT_2019_09: '2019-09',
+ DRAFT_2020_12: '2020-12',
+} as const;
+
+type JsonSchemaDialect = typeof JSON_SCHEMA_DIALECT[keyof typeof JSON_SCHEMA_DIALECT];
+
+const draft07Ajv = new Ajv(AJV_OPTIONS);
+const draft2019Ajv = new Ajv2019(AJV_OPTIONS);
+const draft2020Ajv = new Ajv2020(AJV_OPTIONS);
+
+const DIALECT_BY_META_SCHEMA_URI = new Map<string, JsonSchemaDialect>([
+ ['http://json-schema.org/draft-07/schema', JSON_SCHEMA_DIALECT.DRAFT_07],
+ ['https://json-schema.org/draft/2019-09/schema', JSON_SCHEMA_DIALECT.DRAFT_2019_09],
+ ['https://json-schema.org/draft/2020-12/schema', JSON_SCHEMA_DIALECT.DRAFT_2020_12],
+]);
+
+export class UnsupportedMcpJsonSchemaDialectError extends Error {
+ readonly reason = 'unsupported_json_schema_dialect';
+
+ constructor() {
+ super('MCP tool schema declares an unsupported JSON Schema dialect. Supported dialects are draft-07, 2019-09, and 2020-12.');
+ this.name = 'UnsupportedMcpJsonSchemaDialectError';
+ }
+}
+
+export class UnsupportedMcpJsonSchemaFeatureError extends Error {
+ readonly reason = 'unsupported_json_schema_feature';
+
+ constructor() {
+ super('MCP tool schema uses an unsupported JSON Schema extension.');
+ this.name = 'UnsupportedMcpJsonSchemaFeatureError';
+ }
+}
+
+/**
+ * Compiles an MCP tool schema with the Ajv implementation for its declared
+ * JSON Schema dialect. MCP 2025-11-25 defines 2020-12 as the default when a
+ * schema does not explicitly declare another dialect.
+ */
+export function compileMcpJsonSchemaValidator(schema: unknown): ValidateFunction {
+ rejectAsyncSchema(schema);
+ const dialect = getJsonSchemaDialect(schema);
+
+ switch (dialect) {
+ case JSON_SCHEMA_DIALECT.DRAFT_07:
+ return compileWithAjv(draft07Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2019_09:
+ return compileWithAjv(draft2019Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2020_12:
+ return compileWithAjv(draft2020Ajv, schema);
+ }
+}
+
+export function formatMcpJsonSchemaValidationErrors(
+ errors: ErrorObject[] | null | undefined,
+): string {
+ // Ajv's error representation and formatter are shared across dialects.
+ return draft2020Ajv.errorsText(errors);
+}
+
+function compileWithAjv(
+ ajv: Ajv | Ajv2019 | Ajv2020,
+ schema: unknown,
+): ValidateFunction {
+ // addUsedSchema: false prevents remote root $id values from entering Ajv's
+ // shared schema registry or conflicting across MCP servers.
+ return ajv.compile(schema as AnySchema);
+}
+
+function rejectAsyncSchema(schema: unknown): void {
+ if (
+ typeof schema === 'object'
+ && schema !== null
+ && (schema as Record<string, unknown>).$async === true
+ ) {
+ // $async is an Ajv extension rather than a JSON Schema keyword. The
+ // surrounding AI SDK validation contract is synchronous, so accepting
+ // it would treat a returned Promise as a successful validation.
+ throw new UnsupportedMcpJsonSchemaFeatureError();
+ }
+}
+
+function getJsonSchemaDialect(schema: unknown): JsonSchemaDialect {
+ if (typeof schema !== 'object' || schema === null || !Object.prototype.hasOwnProperty.call(schema, '$schema')) {
+ return JSON_SCHEMA_DIALECT.DRAFT_2020_12;
+ }
+
+ const declaredDialect = (schema as Record<string, unknown>).$schema;
+ if (typeof declaredDialect !== 'string') {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ // An empty URI fragment does not change the selected dialect. Normalizing
+ // it also accepts both forms used by draft-07 schemas in the wild.
+ const normalizedDialect = declaredDialect.endsWith('#')
+ ? declaredDialect.slice(0, -1)
+ : declaredDialect;
+ const dialect = DIALECT_BY_META_SCHEMA_URI.get(normalizedDialect);
+ if (!dialect) {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ return dialect;
+}

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Upgraded `socket.io-parser` to `^4.2.7`. [#1542](https://github.com/sourcebot-dev/sourcebot/pull/1542)
 - Upgraded `fast-uri` to `^3.1.5`. [#1541](https://github.com/sourcebot-dev/sourcebot/pull/1541)
 - Upgraded `ip-address` to `^10.4.0`. [#1540](https://github.com/sourcebot-dev/sourcebot/pull/1540)
+- [EE] Fixed Ask MCP connector tools failing to load when their input schemas use JSON Schema 2019-09 or 2020-12. [#1547](https://github.com/sourcebot-dev/sourcebot/pull/1547)
 
 ## [5.1.5] - 2026-07-31
 

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.test.ts

@@ -0,0 +1,150 @@
+import { describe, expect, test } from 'vitest';
+import {
+ compileMcpJsonSchemaValidator,
+ UnsupportedMcpJsonSchemaDialectError,
+ UnsupportedMcpJsonSchemaFeatureError,
+} from './mcpJsonSchemaValidator';
+
+describe('compileMcpJsonSchemaValidator', () => {
+ test('uses draft-07 when it is explicitly declared', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'http://json-schema.org/draft-07/schema#',
+ type: 'array',
+ items: [{ type: 'string' }],
+ additionalItems: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('uses draft 2019-09 for its declared meta-schema', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2019-09/schema',
+ type: 'object',
+ properties: {
+ known: { type: 'string' },
+ },
+ unevaluatedProperties: false,
+ });
+
+ expect(validate({ known: 'value' })).toBe(true);
+ expect(validate({ known: 'value', extra: true })).toBe(false);
+ expect(validate.errors).toEqual(expect.arrayContaining([
+ expect.objectContaining({ keyword: 'unevaluatedProperties' }),
+ ]));
+ });
+
+ test.each([
+ ['when explicitly declared', 'https://json-schema.org/draft/2020-12/schema'],
+ ['by default when omitted', undefined],
+ ])('uses draft 2020-12 %s', (_name, dialect) => {
+ const validate = compileMcpJsonSchemaValidator({
+ ...(dialect ? { $schema: dialect } : {}),
+ type: 'array',
+ prefixItems: [{ type: 'string' }],
+ items: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate([42])).toBe(false);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('preserves all-errors validation and permits unknown keywords', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ type: 'object',
+ required: ['first', 'second'],
+ unknownServerKeyword: true,
+ });
+
+ expect(validate({})).toBe(false);
+ expect(validate.errors?.filter(error => error.keyword === 'required')).toHaveLength(2);
+ });
+
+ test('does not conflict when separate server schemas reuse the same root ID', () => {
+ const first = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'string',
+ });
+ const second = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'number',
+ });
+
+ expect(first('value')).toBe(true);
+ expect(second(42)).toBe(true);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-07/schema#',
+ 'https://json-schema.org/draft/2019-09/schema',
+ 'https://json-schema.org/draft/2020-12/schema',
+ ])('does not let a remote $id remove the %s meta-schema', (dialect) => {
+ const collidingSchema = compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ $id: dialect,
+ type: 'object',
+ });
+
+ expect(collidingSchema({})).toBe(true);
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ type: 'object',
+ })).not.toThrow();
+ });
+
+ test('resolves document-local 2020-12 references after compilation', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2020-12/schema',
+ $defs: {
+ identifier: { type: 'string', minLength: 1 },
+ },
+ type: 'object',
+ properties: {
+ id: { $ref: '#/$defs/identifier' },
+ },
+ required: ['id'],
+ });
+
+ expect(validate({ id: 'issue-id' })).toBe(true);
+ expect(validate({ id: '' })).toBe(false);
+ });
+
+ test('rejects Ajv asynchronous schemas instead of bypassing validation', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $async: true,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaFeatureError);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-04/schema#',
+ 'https://malicious.example/schema?access_token=secret-token',
+ ])('rejects unsupported dialects without echoing the declaration', (declaredDialect) => {
+ let thrown: unknown;
+ try {
+ compileMcpJsonSchemaValidator({
+ $schema: declaredDialect,
+ type: 'object',
+ });
+ } catch (error) {
+ thrown = error;
+ }
+
+ expect(thrown).toBeInstanceOf(UnsupportedMcpJsonSchemaDialectError);
+ expect(thrown).toMatchObject({
+ name: 'UnsupportedMcpJsonSchemaDialectError',
+ reason: 'unsupported_json_schema_dialect',
+ });
+ expect((thrown as Error).message).not.toContain(declaredDialect);
+ expect((thrown as Error).message).not.toContain('secret-token');
+ });
+
+ test('rejects a non-string declared dialect safely', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: 202012,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaDialectError);
+ });
+});

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.ts

@@ -0,0 +1,116 @@
+import Ajv, { type AnySchema, type ErrorObject, type ValidateFunction } from 'ajv';
+import Ajv2019 from 'ajv/dist/2019.js';
+import Ajv2020 from 'ajv/dist/2020.js';
+
+const AJV_OPTIONS = {
+ addUsedSchema: false,
+ allErrors: true,
+ strict: false,
+} as const;
+
+const JSON_SCHEMA_DIALECT = {
+ DRAFT_07: 'draft-07',
+ DRAFT_2019_09: '2019-09',
+ DRAFT_2020_12: '2020-12',
+} as const;
+
+type JsonSchemaDialect = typeof JSON_SCHEMA_DIALECT[keyof typeof JSON_SCHEMA_DIALECT];
+
+const draft07Ajv = new Ajv(AJV_OPTIONS);
+const draft2019Ajv = new Ajv2019(AJV_OPTIONS);
+const draft2020Ajv = new Ajv2020(AJV_OPTIONS);
+
+const DIALECT_BY_META_SCHEMA_URI = new Map<string, JsonSchemaDialect>([
+ ['http://json-schema.org/draft-07/schema', JSON_SCHEMA_DIALECT.DRAFT_07],
+ ['https://json-schema.org/draft/2019-09/schema', JSON_SCHEMA_DIALECT.DRAFT_2019_09],
+ ['https://json-schema.org/draft/2020-12/schema', JSON_SCHEMA_DIALECT.DRAFT_2020_12],
+]);
+
+export class UnsupportedMcpJsonSchemaDialectError extends Error {
+ readonly reason = 'unsupported_json_schema_dialect';
+
+ constructor() {
+ super('MCP tool schema declares an unsupported JSON Schema dialect. Supported dialects are draft-07, 2019-09, and 2020-12.');
+ this.name = 'UnsupportedMcpJsonSchemaDialectError';
+ }
+}
+
+export class UnsupportedMcpJsonSchemaFeatureError extends Error {
+ readonly reason = 'unsupported_json_schema_feature';
+
+ constructor() {
+ super('MCP tool schema uses an unsupported JSON Schema extension.');
+ this.name = 'UnsupportedMcpJsonSchemaFeatureError';
+ }
+}
+
+/**
+ * Compiles an MCP tool schema with the Ajv implementation for its declared
+ * JSON Schema dialect. MCP 2025-11-25 defines 2020-12 as the default when a
+ * schema does not explicitly declare another dialect.
+ */
+export function compileMcpJsonSchemaValidator(schema: unknown): ValidateFunction {
+ rejectAsyncSchema(schema);
+ const dialect = getJsonSchemaDialect(schema);
+
+ switch (dialect) {
+ case JSON_SCHEMA_DIALECT.DRAFT_07:
+ return compileWithAjv(draft07Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2019_09:
+ return compileWithAjv(draft2019Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2020_12:
+ return compileWithAjv(draft2020Ajv, schema);
+ }
+}
+
+export function formatMcpJsonSchemaValidationErrors(
+ errors: ErrorObject[] | null | undefined,
+): string {
+ // Ajv's error representation and formatter are shared across dialects.
+ return draft2020Ajv.errorsText(errors);
+}
+
+function compileWithAjv(
+ ajv: Ajv | Ajv2019 | Ajv2020,
+ schema: unknown,
+): ValidateFunction {
+ // addUsedSchema: false prevents remote root $id values from entering Ajv's
+ // shared schema registry or conflicting across MCP servers.
+ return ajv.compile(schema as AnySchema);
+}
+
+function rejectAsyncSchema(schema: unknown): void {
+ if (
+ typeof schema === 'object'
+ && schema !== null
+ && (schema as Record<string, unknown>).$async === true
+ ) {
+ // $async is an Ajv extension rather than a JSON Schema keyword. The
+ // surrounding AI SDK validation contract is synchronous, so accepting
+ // it would treat a returned Promise as a successful validation.
+ throw new UnsupportedMcpJsonSchemaFeatureError();
+ }
+}
+
+function getJsonSchemaDialect(schema: unknown): JsonSchemaDialect {
+ if (typeof schema !== 'object' || schema === null || !Object.prototype.hasOwnProperty.call(schema, '$schema')) {
+ return JSON_SCHEMA_DIALECT.DRAFT_2020_12;
+ }
+
+ const declaredDialect = (schema as Record<string, unknown>).$schema;
+ if (typeof declaredDialect !== 'string') {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ // An empty URI fragment does not change the selected dialect. Normalizing
+ // it also accepts both forms used by draft-07 schemas in the wild.
+ const normalizedDialect = declaredDialect.endsWith('#')
+ ? declaredDialect.slice(0, -1)
+ : declaredDialect;
+ const dialect = DIALECT_BY_META_SCHEMA_URI.get(normalizedDialect);
+ if (!dialect) {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ return dialect;
+}

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Upgraded `socket.io-parser` to `^4.2.7`. [#1542](https://github.com/sourcebot-dev/sourcebot/pull/1542)
 - Upgraded `fast-uri` to `^3.1.5`. [#1541](https://github.com/sourcebot-dev/sourcebot/pull/1541)
 - Upgraded `ip-address` to `^10.4.0`. [#1540](https://github.com/sourcebot-dev/sourcebot/pull/1540)
+- [EE] Fixed Ask MCP connector tools failing to load when their input schemas use JSON Schema 2019-09 or 2020-12. [#1547](https://github.com/sourcebot-dev/sourcebot/pull/1547)
 
 ## [5.1.5] - 2026-07-31
 

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.test.ts

@@ -0,0 +1,150 @@
+import { describe, expect, test } from 'vitest';
+import {
+ compileMcpJsonSchemaValidator,
+ UnsupportedMcpJsonSchemaDialectError,
+ UnsupportedMcpJsonSchemaFeatureError,
+} from './mcpJsonSchemaValidator';
+
+describe('compileMcpJsonSchemaValidator', () => {
+ test('uses draft-07 when it is explicitly declared', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'http://json-schema.org/draft-07/schema#',
+ type: 'array',
+ items: [{ type: 'string' }],
+ additionalItems: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('uses draft 2019-09 for its declared meta-schema', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2019-09/schema',
+ type: 'object',
+ properties: {
+ known: { type: 'string' },
+ },
+ unevaluatedProperties: false,
+ });
+
+ expect(validate({ known: 'value' })).toBe(true);
+ expect(validate({ known: 'value', extra: true })).toBe(false);
+ expect(validate.errors).toEqual(expect.arrayContaining([
+ expect.objectContaining({ keyword: 'unevaluatedProperties' }),
+ ]));
+ });
+
+ test.each([
+ ['when explicitly declared', 'https://json-schema.org/draft/2020-12/schema'],
+ ['by default when omitted', undefined],
+ ])('uses draft 2020-12 %s', (_name, dialect) => {
+ const validate = compileMcpJsonSchemaValidator({
+ ...(dialect ? { $schema: dialect } : {}),
+ type: 'array',
+ prefixItems: [{ type: 'string' }],
+ items: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate([42])).toBe(false);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('preserves all-errors validation and permits unknown keywords', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ type: 'object',
+ required: ['first', 'second'],
+ unknownServerKeyword: true,
+ });
+
+ expect(validate({})).toBe(false);
+ expect(validate.errors?.filter(error => error.keyword === 'required')).toHaveLength(2);
+ });
+
+ test('does not conflict when separate server schemas reuse the same root ID', () => {
+ const first = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'string',
+ });
+ const second = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'number',
+ });
+
+ expect(first('value')).toBe(true);
+ expect(second(42)).toBe(true);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-07/schema#',
+ 'https://json-schema.org/draft/2019-09/schema',
+ 'https://json-schema.org/draft/2020-12/schema',
+ ])('does not let a remote $id remove the %s meta-schema', (dialect) => {
+ const collidingSchema = compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ $id: dialect,
+ type: 'object',
+ });
+
+ expect(collidingSchema({})).toBe(true);
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ type: 'object',
+ })).not.toThrow();
+ });
+
+ test('resolves document-local 2020-12 references after compilation', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2020-12/schema',
+ $defs: {
+ identifier: { type: 'string', minLength: 1 },
+ },
+ type: 'object',
+ properties: {
+ id: { $ref: '#/$defs/identifier' },
+ },
+ required: ['id'],
+ });
+
+ expect(validate({ id: 'issue-id' })).toBe(true);
+ expect(validate({ id: '' })).toBe(false);
+ });
+
+ test('rejects Ajv asynchronous schemas instead of bypassing validation', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $async: true,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaFeatureError);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-04/schema#',
+ 'https://malicious.example/schema?access_token=secret-token',
+ ])('rejects unsupported dialects without echoing the declaration', (declaredDialect) => {
+ let thrown: unknown;
+ try {
+ compileMcpJsonSchemaValidator({
+ $schema: declaredDialect,
+ type: 'object',
+ });
+ } catch (error) {
+ thrown = error;
+ }
+
+ expect(thrown).toBeInstanceOf(UnsupportedMcpJsonSchemaDialectError);
+ expect(thrown).toMatchObject({
+ name: 'UnsupportedMcpJsonSchemaDialectError',
+ reason: 'unsupported_json_schema_dialect',
+ });
+ expect((thrown as Error).message).not.toContain(declaredDialect);
+ expect((thrown as Error).message).not.toContain('secret-token');
+ });
+
+ test('rejects a non-string declared dialect safely', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: 202012,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaDialectError);
+ });
+});

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.ts

@@ -0,0 +1,116 @@
+import Ajv, { type AnySchema, type ErrorObject, type ValidateFunction } from 'ajv';
+import Ajv2019 from 'ajv/dist/2019.js';
+import Ajv2020 from 'ajv/dist/2020.js';
+
+const AJV_OPTIONS = {
+ addUsedSchema: false,
+ allErrors: true,
+ strict: false,
+} as const;
+
+const JSON_SCHEMA_DIALECT = {
+ DRAFT_07: 'draft-07',
+ DRAFT_2019_09: '2019-09',
+ DRAFT_2020_12: '2020-12',
+} as const;
+
+type JsonSchemaDialect = typeof JSON_SCHEMA_DIALECT[keyof typeof JSON_SCHEMA_DIALECT];
+
+const draft07Ajv = new Ajv(AJV_OPTIONS);
+const draft2019Ajv = new Ajv2019(AJV_OPTIONS);
+const draft2020Ajv = new Ajv2020(AJV_OPTIONS);
+
+const DIALECT_BY_META_SCHEMA_URI = new Map<string, JsonSchemaDialect>([
+ ['http://json-schema.org/draft-07/schema', JSON_SCHEMA_DIALECT.DRAFT_07],
+ ['https://json-schema.org/draft/2019-09/schema', JSON_SCHEMA_DIALECT.DRAFT_2019_09],
+ ['https://json-schema.org/draft/2020-12/schema', JSON_SCHEMA_DIALECT.DRAFT_2020_12],
+]);
+
+export class UnsupportedMcpJsonSchemaDialectError extends Error {
+ readonly reason = 'unsupported_json_schema_dialect';
+
+ constructor() {
+ super('MCP tool schema declares an unsupported JSON Schema dialect. Supported dialects are draft-07, 2019-09, and 2020-12.');
+ this.name = 'UnsupportedMcpJsonSchemaDialectError';
+ }
+}
+
+export class UnsupportedMcpJsonSchemaFeatureError extends Error {
+ readonly reason = 'unsupported_json_schema_feature';
+
+ constructor() {
+ super('MCP tool schema uses an unsupported JSON Schema extension.');
+ this.name = 'UnsupportedMcpJsonSchemaFeatureError';
+ }
+}
+
+/**
+ * Compiles an MCP tool schema with the Ajv implementation for its declared
+ * JSON Schema dialect. MCP 2025-11-25 defines 2020-12 as the default when a
+ * schema does not explicitly declare another dialect.
+ */
+export function compileMcpJsonSchemaValidator(schema: unknown): ValidateFunction {
+ rejectAsyncSchema(schema);
+ const dialect = getJsonSchemaDialect(schema);
+
+ switch (dialect) {
+ case JSON_SCHEMA_DIALECT.DRAFT_07:
+ return compileWithAjv(draft07Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2019_09:
+ return compileWithAjv(draft2019Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2020_12:
+ return compileWithAjv(draft2020Ajv, schema);
+ }
+}
+
+export function formatMcpJsonSchemaValidationErrors(
+ errors: ErrorObject[] | null | undefined,
+): string {
+ // Ajv's error representation and formatter are shared across dialects.
+ return draft2020Ajv.errorsText(errors);
+}
+
+function compileWithAjv(
+ ajv: Ajv | Ajv2019 | Ajv2020,
+ schema: unknown,
+): ValidateFunction {
+ // addUsedSchema: false prevents remote root $id values from entering Ajv's
+ // shared schema registry or conflicting across MCP servers.
+ return ajv.compile(schema as AnySchema);
+}
+
+function rejectAsyncSchema(schema: unknown): void {
+ if (
+ typeof schema === 'object'
+ && schema !== null
+ && (schema as Record<string, unknown>).$async === true
+ ) {
+ // $async is an Ajv extension rather than a JSON Schema keyword. The
+ // surrounding AI SDK validation contract is synchronous, so accepting
+ // it would treat a returned Promise as a successful validation.
+ throw new UnsupportedMcpJsonSchemaFeatureError();
+ }
+}
+
+function getJsonSchemaDialect(schema: unknown): JsonSchemaDialect {
+ if (typeof schema !== 'object' || schema === null || !Object.prototype.hasOwnProperty.call(schema, '$schema')) {
+ return JSON_SCHEMA_DIALECT.DRAFT_2020_12;
+ }
+
+ const declaredDialect = (schema as Record<string, unknown>).$schema;
+ if (typeof declaredDialect !== 'string') {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ // An empty URI fragment does not change the selected dialect. Normalizing
+ // it also accepts both forms used by draft-07 schemas in the wild.
+ const normalizedDialect = declaredDialect.endsWith('#')
+ ? declaredDialect.slice(0, -1)
+ : declaredDialect;
+ const dialect = DIALECT_BY_META_SCHEMA_URI.get(normalizedDialect);
+ if (!dialect) {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ return dialect;
+}

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Upgraded `socket.io-parser` to `^4.2.7`. [#1542](https://github.com/sourcebot-dev/sourcebot/pull/1542)
 - Upgraded `fast-uri` to `^3.1.5`. [#1541](https://github.com/sourcebot-dev/sourcebot/pull/1541)
 - Upgraded `ip-address` to `^10.4.0`. [#1540](https://github.com/sourcebot-dev/sourcebot/pull/1540)
+- [EE] Fixed Ask MCP connector tools failing to load when their input schemas use JSON Schema 2019-09 or 2020-12. [#1547](https://github.com/sourcebot-dev/sourcebot/pull/1547)
 
 ## [5.1.5] - 2026-07-31
 

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.test.ts

@@ -0,0 +1,150 @@
+import { describe, expect, test } from 'vitest';
+import {
+ compileMcpJsonSchemaValidator,
+ UnsupportedMcpJsonSchemaDialectError,
+ UnsupportedMcpJsonSchemaFeatureError,
+} from './mcpJsonSchemaValidator';
+
+describe('compileMcpJsonSchemaValidator', () => {
+ test('uses draft-07 when it is explicitly declared', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'http://json-schema.org/draft-07/schema#',
+ type: 'array',
+ items: [{ type: 'string' }],
+ additionalItems: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('uses draft 2019-09 for its declared meta-schema', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2019-09/schema',
+ type: 'object',
+ properties: {
+ known: { type: 'string' },
+ },
+ unevaluatedProperties: false,
+ });
+
+ expect(validate({ known: 'value' })).toBe(true);
+ expect(validate({ known: 'value', extra: true })).toBe(false);
+ expect(validate.errors).toEqual(expect.arrayContaining([
+ expect.objectContaining({ keyword: 'unevaluatedProperties' }),
+ ]));
+ });
+
+ test.each([
+ ['when explicitly declared', 'https://json-schema.org/draft/2020-12/schema'],
+ ['by default when omitted', undefined],
+ ])('uses draft 2020-12 %s', (_name, dialect) => {
+ const validate = compileMcpJsonSchemaValidator({
+ ...(dialect ? { $schema: dialect } : {}),
+ type: 'array',
+ prefixItems: [{ type: 'string' }],
+ items: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate([42])).toBe(false);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('preserves all-errors validation and permits unknown keywords', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ type: 'object',
+ required: ['first', 'second'],
+ unknownServerKeyword: true,
+ });
+
+ expect(validate({})).toBe(false);
+ expect(validate.errors?.filter(error => error.keyword === 'required')).toHaveLength(2);
+ });
+
+ test('does not conflict when separate server schemas reuse the same root ID', () => {
+ const first = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'string',
+ });
+ const second = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'number',
+ });
+
+ expect(first('value')).toBe(true);
+ expect(second(42)).toBe(true);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-07/schema#',
+ 'https://json-schema.org/draft/2019-09/schema',
+ 'https://json-schema.org/draft/2020-12/schema',
+ ])('does not let a remote $id remove the %s meta-schema', (dialect) => {
+ const collidingSchema = compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ $id: dialect,
+ type: 'object',
+ });
+
+ expect(collidingSchema({})).toBe(true);
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ type: 'object',
+ })).not.toThrow();
+ });
+
+ test('resolves document-local 2020-12 references after compilation', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2020-12/schema',
+ $defs: {
+ identifier: { type: 'string', minLength: 1 },
+ },
+ type: 'object',
+ properties: {
+ id: { $ref: '#/$defs/identifier' },
+ },
+ required: ['id'],
+ });
+
+ expect(validate({ id: 'issue-id' })).toBe(true);
+ expect(validate({ id: '' })).toBe(false);
+ });
+
+ test('rejects Ajv asynchronous schemas instead of bypassing validation', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $async: true,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaFeatureError);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-04/schema#',
+ 'https://malicious.example/schema?access_token=secret-token',
+ ])('rejects unsupported dialects without echoing the declaration', (declaredDialect) => {
+ let thrown: unknown;
+ try {
+ compileMcpJsonSchemaValidator({
+ $schema: declaredDialect,
+ type: 'object',
+ });
+ } catch (error) {
+ thrown = error;
+ }
+
+ expect(thrown).toBeInstanceOf(UnsupportedMcpJsonSchemaDialectError);
+ expect(thrown).toMatchObject({
+ name: 'UnsupportedMcpJsonSchemaDialectError',
+ reason: 'unsupported_json_schema_dialect',
+ });
+ expect((thrown as Error).message).not.toContain(declaredDialect);
+ expect((thrown as Error).message).not.toContain('secret-token');
+ });
+
+ test('rejects a non-string declared dialect safely', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: 202012,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaDialectError);
+ });
+});

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.ts

@@ -0,0 +1,116 @@
+import Ajv, { type AnySchema, type ErrorObject, type ValidateFunction } from 'ajv';
+import Ajv2019 from 'ajv/dist/2019.js';
+import Ajv2020 from 'ajv/dist/2020.js';
+
+const AJV_OPTIONS = {
+ addUsedSchema: false,
+ allErrors: true,
+ strict: false,
+} as const;
+
+const JSON_SCHEMA_DIALECT = {
+ DRAFT_07: 'draft-07',
+ DRAFT_2019_09: '2019-09',
+ DRAFT_2020_12: '2020-12',
+} as const;
+
+type JsonSchemaDialect = typeof JSON_SCHEMA_DIALECT[keyof typeof JSON_SCHEMA_DIALECT];
+
+const draft07Ajv = new Ajv(AJV_OPTIONS);
+const draft2019Ajv = new Ajv2019(AJV_OPTIONS);
+const draft2020Ajv = new Ajv2020(AJV_OPTIONS);
+
+const DIALECT_BY_META_SCHEMA_URI = new Map<string, JsonSchemaDialect>([
+ ['http://json-schema.org/draft-07/schema', JSON_SCHEMA_DIALECT.DRAFT_07],
+ ['https://json-schema.org/draft/2019-09/schema', JSON_SCHEMA_DIALECT.DRAFT_2019_09],
+ ['https://json-schema.org/draft/2020-12/schema', JSON_SCHEMA_DIALECT.DRAFT_2020_12],
+]);
+
+export class UnsupportedMcpJsonSchemaDialectError extends Error {
+ readonly reason = 'unsupported_json_schema_dialect';
+
+ constructor() {
+ super('MCP tool schema declares an unsupported JSON Schema dialect. Supported dialects are draft-07, 2019-09, and 2020-12.');
+ this.name = 'UnsupportedMcpJsonSchemaDialectError';
+ }
+}
+
+export class UnsupportedMcpJsonSchemaFeatureError extends Error {
+ readonly reason = 'unsupported_json_schema_feature';
+
+ constructor() {
+ super('MCP tool schema uses an unsupported JSON Schema extension.');
+ this.name = 'UnsupportedMcpJsonSchemaFeatureError';
+ }
+}
+
+/**
+ * Compiles an MCP tool schema with the Ajv implementation for its declared
+ * JSON Schema dialect. MCP 2025-11-25 defines 2020-12 as the default when a
+ * schema does not explicitly declare another dialect.
+ */
+export function compileMcpJsonSchemaValidator(schema: unknown): ValidateFunction {
+ rejectAsyncSchema(schema);
+ const dialect = getJsonSchemaDialect(schema);
+
+ switch (dialect) {
+ case JSON_SCHEMA_DIALECT.DRAFT_07:
+ return compileWithAjv(draft07Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2019_09:
+ return compileWithAjv(draft2019Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2020_12:
+ return compileWithAjv(draft2020Ajv, schema);
+ }
+}
+
+export function formatMcpJsonSchemaValidationErrors(
+ errors: ErrorObject[] | null | undefined,
+): string {
+ // Ajv's error representation and formatter are shared across dialects.
+ return draft2020Ajv.errorsText(errors);
+}
+
+function compileWithAjv(
+ ajv: Ajv | Ajv2019 | Ajv2020,
+ schema: unknown,
+): ValidateFunction {
+ // addUsedSchema: false prevents remote root $id values from entering Ajv's
+ // shared schema registry or conflicting across MCP servers.
+ return ajv.compile(schema as AnySchema);
+}
+
+function rejectAsyncSchema(schema: unknown): void {
+ if (
+ typeof schema === 'object'
+ && schema !== null
+ && (schema as Record<string, unknown>).$async === true
+ ) {
+ // $async is an Ajv extension rather than a JSON Schema keyword. The
+ // surrounding AI SDK validation contract is synchronous, so accepting
+ // it would treat a returned Promise as a successful validation.
+ throw new UnsupportedMcpJsonSchemaFeatureError();
+ }
+}
+
+function getJsonSchemaDialect(schema: unknown): JsonSchemaDialect {
+ if (typeof schema !== 'object' || schema === null || !Object.prototype.hasOwnProperty.call(schema, '$schema')) {
+ return JSON_SCHEMA_DIALECT.DRAFT_2020_12;
+ }
+
+ const declaredDialect = (schema as Record<string, unknown>).$schema;
+ if (typeof declaredDialect !== 'string') {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ // An empty URI fragment does not change the selected dialect. Normalizing
+ // it also accepts both forms used by draft-07 schemas in the wild.
+ const normalizedDialect = declaredDialect.endsWith('#')
+ ? declaredDialect.slice(0, -1)
+ : declaredDialect;
+ const dialect = DIALECT_BY_META_SCHEMA_URI.get(normalizedDialect);
+ if (!dialect) {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ return dialect;
+}

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Upgraded `socket.io-parser` to `^4.2.7`. [#1542](https://github.com/sourcebot-dev/sourcebot/pull/1542)
 - Upgraded `fast-uri` to `^3.1.5`. [#1541](https://github.com/sourcebot-dev/sourcebot/pull/1541)
 - Upgraded `ip-address` to `^10.4.0`. [#1540](https://github.com/sourcebot-dev/sourcebot/pull/1540)
+- [EE] Fixed Ask MCP connector tools failing to load when their input schemas use JSON Schema 2019-09 or 2020-12. [#1547](https://github.com/sourcebot-dev/sourcebot/pull/1547)
 
 ## [5.1.5] - 2026-07-31
 

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.test.ts

@@ -0,0 +1,150 @@
+import { describe, expect, test } from 'vitest';
+import {
+ compileMcpJsonSchemaValidator,
+ UnsupportedMcpJsonSchemaDialectError,
+ UnsupportedMcpJsonSchemaFeatureError,
+} from './mcpJsonSchemaValidator';
+
+describe('compileMcpJsonSchemaValidator', () => {
+ test('uses draft-07 when it is explicitly declared', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'http://json-schema.org/draft-07/schema#',
+ type: 'array',
+ items: [{ type: 'string' }],
+ additionalItems: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('uses draft 2019-09 for its declared meta-schema', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2019-09/schema',
+ type: 'object',
+ properties: {
+ known: { type: 'string' },
+ },
+ unevaluatedProperties: false,
+ });
+
+ expect(validate({ known: 'value' })).toBe(true);
+ expect(validate({ known: 'value', extra: true })).toBe(false);
+ expect(validate.errors).toEqual(expect.arrayContaining([
+ expect.objectContaining({ keyword: 'unevaluatedProperties' }),
+ ]));
+ });
+
+ test.each([
+ ['when explicitly declared', 'https://json-schema.org/draft/2020-12/schema'],
+ ['by default when omitted', undefined],
+ ])('uses draft 2020-12 %s', (_name, dialect) => {
+ const validate = compileMcpJsonSchemaValidator({
+ ...(dialect ? { $schema: dialect } : {}),
+ type: 'array',
+ prefixItems: [{ type: 'string' }],
+ items: false,
+ });
+
+ expect(validate(['valid'])).toBe(true);
+ expect(validate([42])).toBe(false);
+ expect(validate(['valid', 'extra'])).toBe(false);
+ });
+
+ test('preserves all-errors validation and permits unknown keywords', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ type: 'object',
+ required: ['first', 'second'],
+ unknownServerKeyword: true,
+ });
+
+ expect(validate({})).toBe(false);
+ expect(validate.errors?.filter(error => error.keyword === 'required')).toHaveLength(2);
+ });
+
+ test('does not conflict when separate server schemas reuse the same root ID', () => {
+ const first = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'string',
+ });
+ const second = compileMcpJsonSchemaValidator({
+ $id: 'https://schemas.example.com/tool-input',
+ type: 'number',
+ });
+
+ expect(first('value')).toBe(true);
+ expect(second(42)).toBe(true);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-07/schema#',
+ 'https://json-schema.org/draft/2019-09/schema',
+ 'https://json-schema.org/draft/2020-12/schema',
+ ])('does not let a remote $id remove the %s meta-schema', (dialect) => {
+ const collidingSchema = compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ $id: dialect,
+ type: 'object',
+ });
+
+ expect(collidingSchema({})).toBe(true);
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: dialect,
+ type: 'object',
+ })).not.toThrow();
+ });
+
+ test('resolves document-local 2020-12 references after compilation', () => {
+ const validate = compileMcpJsonSchemaValidator({
+ $schema: 'https://json-schema.org/draft/2020-12/schema',
+ $defs: {
+ identifier: { type: 'string', minLength: 1 },
+ },
+ type: 'object',
+ properties: {
+ id: { $ref: '#/$defs/identifier' },
+ },
+ required: ['id'],
+ });
+
+ expect(validate({ id: 'issue-id' })).toBe(true);
+ expect(validate({ id: '' })).toBe(false);
+ });
+
+ test('rejects Ajv asynchronous schemas instead of bypassing validation', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $async: true,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaFeatureError);
+ });
+
+ test.each([
+ 'http://json-schema.org/draft-04/schema#',
+ 'https://malicious.example/schema?access_token=secret-token',
+ ])('rejects unsupported dialects without echoing the declaration', (declaredDialect) => {
+ let thrown: unknown;
+ try {
+ compileMcpJsonSchemaValidator({
+ $schema: declaredDialect,
+ type: 'object',
+ });
+ } catch (error) {
+ thrown = error;
+ }
+
+ expect(thrown).toBeInstanceOf(UnsupportedMcpJsonSchemaDialectError);
+ expect(thrown).toMatchObject({
+ name: 'UnsupportedMcpJsonSchemaDialectError',
+ reason: 'unsupported_json_schema_dialect',
+ });
+ expect((thrown as Error).message).not.toContain(declaredDialect);
+ expect((thrown as Error).message).not.toContain('secret-token');
+ });
+
+ test('rejects a non-string declared dialect safely', () => {
+ expect(() => compileMcpJsonSchemaValidator({
+ $schema: 202012,
+ type: 'object',
+ })).toThrow(UnsupportedMcpJsonSchemaDialectError);
+ });
+});

packages/web/src/ee/features/chat/mcp/mcpJsonSchemaValidator.ts

@@ -0,0 +1,116 @@
+import Ajv, { type AnySchema, type ErrorObject, type ValidateFunction } from 'ajv';
+import Ajv2019 from 'ajv/dist/2019.js';
+import Ajv2020 from 'ajv/dist/2020.js';
+
+const AJV_OPTIONS = {
+ addUsedSchema: false,
+ allErrors: true,
+ strict: false,
+} as const;
+
+const JSON_SCHEMA_DIALECT = {
+ DRAFT_07: 'draft-07',
+ DRAFT_2019_09: '2019-09',
+ DRAFT_2020_12: '2020-12',
+} as const;
+
+type JsonSchemaDialect = typeof JSON_SCHEMA_DIALECT[keyof typeof JSON_SCHEMA_DIALECT];
+
+const draft07Ajv = new Ajv(AJV_OPTIONS);
+const draft2019Ajv = new Ajv2019(AJV_OPTIONS);
+const draft2020Ajv = new Ajv2020(AJV_OPTIONS);
+
+const DIALECT_BY_META_SCHEMA_URI = new Map<string, JsonSchemaDialect>([
+ ['http://json-schema.org/draft-07/schema', JSON_SCHEMA_DIALECT.DRAFT_07],
+ ['https://json-schema.org/draft/2019-09/schema', JSON_SCHEMA_DIALECT.DRAFT_2019_09],
+ ['https://json-schema.org/draft/2020-12/schema', JSON_SCHEMA_DIALECT.DRAFT_2020_12],
+]);
+
+export class UnsupportedMcpJsonSchemaDialectError extends Error {
+ readonly reason = 'unsupported_json_schema_dialect';
+
+ constructor() {
+ super('MCP tool schema declares an unsupported JSON Schema dialect. Supported dialects are draft-07, 2019-09, and 2020-12.');
+ this.name = 'UnsupportedMcpJsonSchemaDialectError';
+ }
+}
+
+export class UnsupportedMcpJsonSchemaFeatureError extends Error {
+ readonly reason = 'unsupported_json_schema_feature';
+
+ constructor() {
+ super('MCP tool schema uses an unsupported JSON Schema extension.');
+ this.name = 'UnsupportedMcpJsonSchemaFeatureError';
+ }
+}
+
+/**
+ * Compiles an MCP tool schema with the Ajv implementation for its declared
+ * JSON Schema dialect. MCP 2025-11-25 defines 2020-12 as the default when a
+ * schema does not explicitly declare another dialect.
+ */
+export function compileMcpJsonSchemaValidator(schema: unknown): ValidateFunction {
+ rejectAsyncSchema(schema);
+ const dialect = getJsonSchemaDialect(schema);
+
+ switch (dialect) {
+ case JSON_SCHEMA_DIALECT.DRAFT_07:
+ return compileWithAjv(draft07Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2019_09:
+ return compileWithAjv(draft2019Ajv, schema);
+ case JSON_SCHEMA_DIALECT.DRAFT_2020_12:
+ return compileWithAjv(draft2020Ajv, schema);
+ }
+}
+
+export function formatMcpJsonSchemaValidationErrors(
+ errors: ErrorObject[] | null | undefined,
+): string {
+ // Ajv's error representation and formatter are shared across dialects.
+ return draft2020Ajv.errorsText(errors);
+}
+
+function compileWithAjv(
+ ajv: Ajv | Ajv2019 | Ajv2020,
+ schema: unknown,
+): ValidateFunction {
+ // addUsedSchema: false prevents remote root $id values from entering Ajv's
+ // shared schema registry or conflicting across MCP servers.
+ return ajv.compile(schema as AnySchema);
+}
+
+function rejectAsyncSchema(schema: unknown): void {
+ if (
+ typeof schema === 'object'
+ && schema !== null
+ && (schema as Record<string, unknown>).$async === true
+ ) {
+ // $async is an Ajv extension rather than a JSON Schema keyword. The
+ // surrounding AI SDK validation contract is synchronous, so accepting
+ // it would treat a returned Promise as a successful validation.
+ throw new UnsupportedMcpJsonSchemaFeatureError();
+ }
+}
+
+function getJsonSchemaDialect(schema: unknown): JsonSchemaDialect {
+ if (typeof schema !== 'object' || schema === null || !Object.prototype.hasOwnProperty.call(schema, '$schema')) {
+ return JSON_SCHEMA_DIALECT.DRAFT_2020_12;
+ }
+
+ const declaredDialect = (schema as Record<string, unknown>).$schema;
+ if (typeof declaredDialect !== 'string') {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ // An empty URI fragment does not change the selected dialect. Normalizing
+ // it also accepts both forms used by draft-07 schemas in the wild.
+ const normalizedDialect = declaredDialect.endsWith('#')
+ ? declaredDialect.slice(0, -1)
+ : declaredDialect;
+ const dialect = DIALECT_BY_META_SCHEMA_URI.get(normalizedDialect);
+ if (!dialect) {
+ throw new UnsupportedMcpJsonSchemaDialectError();
+ }
+
+ return dialect;
+}