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feat(core): custom-method support (3-arg setRequestHandler + request schema overload) - #1974

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Stacks on #1976 (_wrapHandler hook refactor). Review that first.

Custom (non-spec) method support: typed registration and sending. Replaces the #1891 / #1916 / #1917 chain with a single overload-based design. Protocol stays private (dispatcher RFC handles framework subclassing).

  • setRequestHandler / setNotificationHandler gain a 3-arg form: (method, { params, result? }, handler). params is any Standard Schema; the handler receives the parsed params object. _meta is stripped before validation (available as ctx.mcpReq._meta). Supplying result types the handler's return value.
  • request() and ctx.mcpReq.send gain a (req, resultSchema) overload for typed custom-method results.

Spec-method calls are unchanged (2-arg setRequestHandler, 1-arg request()). 2 overloads each on setRequestHandler/setNotificationHandler/request.

Motivation and Context

v2-main's setRequestHandler/request() only accept the closed RequestMethod/NotificationMethod unions, so vendor-prefixed methods (which the spec permits) cannot be registered or sent. The #1891/#1916/#1917 stack solved this with both v1-compat ZodSchema overloads and a ProtocolSpec<SpecT> typed-vocabulary mechanism; this PR is the minimal cut: one new overload per method. See discussion on #1891.

How Has This Been Tested?

packages/core/test/shared/customMethods.test.ts (9 tests): 3-arg registration, params validation, _meta strip, typed return via result, request() schema overload, mcpReq.send schema overload. typecheck/lint/build/docs/test:all clean locally.

Breaking Changes

None to v2-main. v1's setRequestHandler(ZodSchema, h) form is not restored here; it is mechanically codemod-able to the 3-arg form (#1950).

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Breaking change (fix or feature that would cause existing functionality to change)
  • Documentation update

Checklist

  • I have read the MCP Documentation
  • My code follows the repository's style guidelines
  • New and existing tests pass locally
  • I have added appropriate error handling
  • I have added or updated documentation as needed

Additional context

Alternative to #1891 / #1916 / #1917 (which stay open for comparison). Internally widens _requestWithSchema and the TaskManager send-chain from Zod-only AnySchema to StandardSchemaV1; Zod schemas implement StandardSchemaV1 so existing internal callers are unchanged.

Protocol is intentionally not exported in this PR. A separate dispatcher RFC (gist) covers the framework-subclassing use case; until that lands, Protocol stays internal-only.

Includes a _wrapHandler protected hook so subclass per-method validation (tools/call in Server, elicitation/create/sampling/createMessage in Client) does not require redeclaring setRequestHandler's overload set. The hook runs for both registration paths; validation behavior is unchanged.

@felixweinbergerfelixweinberger added the v2-bc v2 backwards-compatibility series label Apr 28, 2026
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@felixweinbergerfelixweinberger changed the title feat(core): custom-method support (3-arg setRequestHandler + request schema overload + export Protocol)feat(core): custom-method support (3-arg setRequestHandler + request schema overload)Apr 28, 2026
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LGTM, some potential nits, not blocking.

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@felixweinberger
feat(core): 3-arg setRequestHandler/setNotificationHandler and reques…
690af0d
…t()/mcpReq.send schema overloads for custom methods
@felixweinberger
fix: address review — setNotificationHandler 3-arg passes raw notific…
10a7878
…ation as 2nd arg; export StandardSchemaV1; fix example headers
@felixweinberger
fix: address review — assertCapability* params as RequestMethod|strin…
34a4fd5
…g for discoverability (KKonstantinov)
@felixweinberger
fix: address review — guard cancel() once response received (abort ra…
dc09b1d
…ce during async result validation); add core to changeset; setNotificationHandler JSDoc notes 2nd arg
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feat(core): custom-method support (3-arg setRequestHandler + request schema overload) by felixweinberger · Pull Request #1974 · modelcontextprotocol/typescript-sdk · GitHub
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feat(core): custom-method support (3-arg setRequestHandler + request schema overload) - #1974
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feat(core): custom-method support (3-arg setRequestHandler + request schema overload)#1974
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Stacks on #1976 (_wrapHandler hook refactor). Review that first.
Custom (non-spec) method support: typed registration and sending. Replaces the #1891 / #1916 / #1917 chain with a single overload-based design. Protocol stays private (dispatcher RFC handles framework subclassing).
  • setRequestHandler / setNotificationHandler gain a 3-arg form: (method, { params, result? }, handler). params is any Standard Schema; the handler receives the parsed params object. _meta is stripped before validation (available as ctx.mcpReq._meta). Supplying result types the handler's return value.
  • request() and ctx.mcpReq.send gain a (req, resultSchema) overload for typed custom-method results.
Spec-method calls are unchanged (2-arg setRequestHandler, 1-arg request()). 2 overloads each on setRequestHandler/setNotificationHandler/request.
Motivation and Context
v2-main's setRequestHandler/request() only accept the closed RequestMethod/NotificationMethod unions, so vendor-prefixed methods (which the spec permits) cannot be registered or sent. The #1891/#1916/#1917 stack solved this with both v1-compat ZodSchema overloads and a ProtocolSpec<SpecT> typed-vocabulary mechanism; this PR is the minimal cut: one new overload per method. See discussion on #1891.
How Has This Been Tested?
packages/core/test/shared/customMethods.test.ts (9 tests): 3-arg registration, params validation, _meta strip, typed return via result, request() schema overload, mcpReq.send schema overload. typecheck/lint/build/docs/test:all clean locally.
Breaking Changes
None to v2-main. v1's setRequestHandler(ZodSchema, h) form is not restored here; it is mechanically codemod-able to the 3-arg form (#1950).
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
Alternative to #1891 / #1916 / #1917 (which stay open for comparison). Internally widens _requestWithSchema and the TaskManager send-chain from Zod-only AnySchema to StandardSchemaV1; Zod schemas implement StandardSchemaV1 so existing internal callers are unchanged.
Protocol is intentionally not exported in this PR. A separate dispatcher RFC (gist) covers the framework-subclassing use case; until that lands, Protocol stays internal-only.
Includes a _wrapHandler protected hook so subclass per-method validation (tools/call in Server, elicitation/create/sampling/createMessage in Client) does not require redeclaring setRequestHandler's overload set. The hook runs for both registration paths; validation behavior is unchanged.
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LGTM, some potential nits, not blocking.
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feat(core): 3-arg setRequestHandler/setNotificationHandler and reques…
690af0d
…t()/mcpReq.send schema overloads for custom methods
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fix: address review — setNotificationHandler 3-arg passes raw notific…
10a7878
…ation as 2nd arg; export StandardSchemaV1; fix example headers
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fix: address review — assertCapability* params as RequestMethod|strin…
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…g for discoverability (KKonstantinov)
@felixweinberger
fix: address review — guard cancel() once response received (abort ra…
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…ce during async result validation); add core to changeset; setNotificationHandler JSDoc notes 2nd arg
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feat(core): custom-method support (3-arg setRequestHandler + request schema overload) by felixweinberger · Pull Request #1974 · modelcontextprotocol/typescript-sdk · GitHub
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feat(core): custom-method support (3-arg setRequestHandler + request schema overload) - #1974
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Stacks on #1976 (_wrapHandler hook refactor). Review that first.
Custom (non-spec) method support: typed registration and sending. Replaces the #1891 / #1916 / #1917 chain with a single overload-based design. Protocol stays private (dispatcher RFC handles framework subclassing).
  • setRequestHandler / setNotificationHandler gain a 3-arg form: (method, { params, result? }, handler). params is any Standard Schema; the handler receives the parsed params object. _meta is stripped before validation (available as ctx.mcpReq._meta). Supplying result types the handler's return value.
  • request() and ctx.mcpReq.send gain a (req, resultSchema) overload for typed custom-method results.
Spec-method calls are unchanged (2-arg setRequestHandler, 1-arg request()). 2 overloads each on setRequestHandler/setNotificationHandler/request.
Motivation and Context
v2-main's setRequestHandler/request() only accept the closed RequestMethod/NotificationMethod unions, so vendor-prefixed methods (which the spec permits) cannot be registered or sent. The #1891/#1916/#1917 stack solved this with both v1-compat ZodSchema overloads and a ProtocolSpec<SpecT> typed-vocabulary mechanism; this PR is the minimal cut: one new overload per method. See discussion on #1891.
How Has This Been Tested?
packages/core/test/shared/customMethods.test.ts (9 tests): 3-arg registration, params validation, _meta strip, typed return via result, request() schema overload, mcpReq.send schema overload. typecheck/lint/build/docs/test:all clean locally.
Breaking Changes
None to v2-main. v1's setRequestHandler(ZodSchema, h) form is not restored here; it is mechanically codemod-able to the 3-arg form (#1950).
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
Alternative to #1891 / #1916 / #1917 (which stay open for comparison). Internally widens _requestWithSchema and the TaskManager send-chain from Zod-only AnySchema to StandardSchemaV1; Zod schemas implement StandardSchemaV1 so existing internal callers are unchanged.
Protocol is intentionally not exported in this PR. A separate dispatcher RFC (gist) covers the framework-subclassing use case; until that lands, Protocol stays internal-only.
Includes a _wrapHandler protected hook so subclass per-method validation (tools/call in Server, elicitation/create/sampling/createMessage in Client) does not require redeclaring setRequestHandler's overload set. The hook runs for both registration paths; validation behavior is unchanged.
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feat(core): custom-method support (3-arg setRequestHandler + request schema overload) by felixweinberger · Pull Request #1974 · modelcontextprotocol/typescript-sdk · GitHub
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Stacks on #1976 (_wrapHandler hook refactor). Review that first.
Custom (non-spec) method support: typed registration and sending. Replaces the #1891 / #1916 / #1917 chain with a single overload-based design. Protocol stays private (dispatcher RFC handles framework subclassing).
  • setRequestHandler / setNotificationHandler gain a 3-arg form: (method, { params, result? }, handler). params is any Standard Schema; the handler receives the parsed params object. _meta is stripped before validation (available as ctx.mcpReq._meta). Supplying result types the handler's return value.
  • request() and ctx.mcpReq.send gain a (req, resultSchema) overload for typed custom-method results.
Spec-method calls are unchanged (2-arg setRequestHandler, 1-arg request()). 2 overloads each on setRequestHandler/setNotificationHandler/request.
Motivation and Context
v2-main's setRequestHandler/request() only accept the closed RequestMethod/NotificationMethod unions, so vendor-prefixed methods (which the spec permits) cannot be registered or sent. The #1891/#1916/#1917 stack solved this with both v1-compat ZodSchema overloads and a ProtocolSpec<SpecT> typed-vocabulary mechanism; this PR is the minimal cut: one new overload per method. See discussion on #1891.
How Has This Been Tested?
packages/core/test/shared/customMethods.test.ts (9 tests): 3-arg registration, params validation, _meta strip, typed return via result, request() schema overload, mcpReq.send schema overload. typecheck/lint/build/docs/test:all clean locally.
Breaking Changes
None to v2-main. v1's setRequestHandler(ZodSchema, h) form is not restored here; it is mechanically codemod-able to the 3-arg form (#1950).
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
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  •  Breaking change (fix or feature that would cause existing functionality to change)
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Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
Alternative to #1891 / #1916 / #1917 (which stay open for comparison). Internally widens _requestWithSchema and the TaskManager send-chain from Zod-only AnySchema to StandardSchemaV1; Zod schemas implement StandardSchemaV1 so existing internal callers are unchanged.
Protocol is intentionally not exported in this PR. A separate dispatcher RFC (gist) covers the framework-subclassing use case; until that lands, Protocol stays internal-only.
Includes a _wrapHandler protected hook so subclass per-method validation (tools/call in Server, elicitation/create/sampling/createMessage in Client) does not require redeclaring setRequestHandler's overload set. The hook runs for both registration paths; validation behavior is unchanged.
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LGTM, some potential nits, not blocking.
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fix: address review — setNotificationHandler 3-arg passes raw notific…
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fix: address review — assertCapability* params as RequestMethod|strin…
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…g for discoverability (KKonstantinov)
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fix: address review — guard cancel() once response received (abort ra…
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feat(core): custom-method support (3-arg setRequestHandler + request schema overload) by felixweinberger · Pull Request #1974 · modelcontextprotocol/typescript-sdk · GitHub
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feat(core): custom-method support (3-arg setRequestHandler + request schema overload) - #1974
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Stacks on #1976 (_wrapHandler hook refactor). Review that first.
Custom (non-spec) method support: typed registration and sending. Replaces the #1891 / #1916 / #1917 chain with a single overload-based design. Protocol stays private (dispatcher RFC handles framework subclassing).
  • setRequestHandler / setNotificationHandler gain a 3-arg form: (method, { params, result? }, handler). params is any Standard Schema; the handler receives the parsed params object. _meta is stripped before validation (available as ctx.mcpReq._meta). Supplying result types the handler's return value.
  • request() and ctx.mcpReq.send gain a (req, resultSchema) overload for typed custom-method results.
Spec-method calls are unchanged (2-arg setRequestHandler, 1-arg request()). 2 overloads each on setRequestHandler/setNotificationHandler/request.
Motivation and Context
v2-main's setRequestHandler/request() only accept the closed RequestMethod/NotificationMethod unions, so vendor-prefixed methods (which the spec permits) cannot be registered or sent. The #1891/#1916/#1917 stack solved this with both v1-compat ZodSchema overloads and a ProtocolSpec<SpecT> typed-vocabulary mechanism; this PR is the minimal cut: one new overload per method. See discussion on #1891.
How Has This Been Tested?
packages/core/test/shared/customMethods.test.ts (9 tests): 3-arg registration, params validation, _meta strip, typed return via result, request() schema overload, mcpReq.send schema overload. typecheck/lint/build/docs/test:all clean locally.
Breaking Changes
None to v2-main. v1's setRequestHandler(ZodSchema, h) form is not restored here; it is mechanically codemod-able to the 3-arg form (#1950).
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
Alternative to #1891 / #1916 / #1917 (which stay open for comparison). Internally widens _requestWithSchema and the TaskManager send-chain from Zod-only AnySchema to StandardSchemaV1; Zod schemas implement StandardSchemaV1 so existing internal callers are unchanged.
Protocol is intentionally not exported in this PR. A separate dispatcher RFC (gist) covers the framework-subclassing use case; until that lands, Protocol stays internal-only.
Includes a _wrapHandler protected hook so subclass per-method validation (tools/call in Server, elicitation/create/sampling/createMessage in Client) does not require redeclaring setRequestHandler's overload set. The hook runs for both registration paths; validation behavior is unchanged.
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feat(core): custom-method support (3-arg setRequestHandler + request schema overload) by felixweinberger · Pull Request #1974 · modelcontextprotocol/typescript-sdk · GitHub
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Stacks on #1976 (_wrapHandler hook refactor). Review that first.
Custom (non-spec) method support: typed registration and sending. Replaces the #1891 / #1916 / #1917 chain with a single overload-based design. Protocol stays private (dispatcher RFC handles framework subclassing).
  • setRequestHandler / setNotificationHandler gain a 3-arg form: (method, { params, result? }, handler). params is any Standard Schema; the handler receives the parsed params object. _meta is stripped before validation (available as ctx.mcpReq._meta). Supplying result types the handler's return value.
  • request() and ctx.mcpReq.send gain a (req, resultSchema) overload for typed custom-method results.
Spec-method calls are unchanged (2-arg setRequestHandler, 1-arg request()). 2 overloads each on setRequestHandler/setNotificationHandler/request.
Motivation and Context
v2-main's setRequestHandler/request() only accept the closed RequestMethod/NotificationMethod unions, so vendor-prefixed methods (which the spec permits) cannot be registered or sent. The #1891/#1916/#1917 stack solved this with both v1-compat ZodSchema overloads and a ProtocolSpec<SpecT> typed-vocabulary mechanism; this PR is the minimal cut: one new overload per method. See discussion on #1891.
How Has This Been Tested?
packages/core/test/shared/customMethods.test.ts (9 tests): 3-arg registration, params validation, _meta strip, typed return via result, request() schema overload, mcpReq.send schema overload. typecheck/lint/build/docs/test:all clean locally.
Breaking Changes
None to v2-main. v1's setRequestHandler(ZodSchema, h) form is not restored here; it is mechanically codemod-able to the 3-arg form (#1950).
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
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  •  Breaking change (fix or feature that would cause existing functionality to change)
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  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
Alternative to #1891 / #1916 / #1917 (which stay open for comparison). Internally widens _requestWithSchema and the TaskManager send-chain from Zod-only AnySchema to StandardSchemaV1; Zod schemas implement StandardSchemaV1 so existing internal callers are unchanged.
Protocol is intentionally not exported in this PR. A separate dispatcher RFC (gist) covers the framework-subclassing use case; until that lands, Protocol stays internal-only.
Includes a _wrapHandler protected hook so subclass per-method validation (tools/call in Server, elicitation/create/sampling/createMessage in Client) does not require redeclaring setRequestHandler's overload set. The hook runs for both registration paths; validation behavior is unchanged.
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@modelcontextprotocol/express
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@modelcontextprotocol/fastify
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@modelcontextprotocol/hono
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LGTM, some potential nits, not blocking.
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fix: address review — setNotificationHandler 3-arg passes raw notific…
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fix: address review — assertCapability* params as RequestMethod|strin…
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fix: address review — guard cancel() once response received (abort ra…
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feat(core): custom-method support (3-arg setRequestHandler + request schema overload) by felixweinberger · Pull Request #1974 · modelcontextprotocol/typescript-sdk · GitHub
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feat(core): custom-method support (3-arg setRequestHandler + request schema overload) - #1974
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Stacks on #1976 (_wrapHandler hook refactor). Review that first.
Custom (non-spec) method support: typed registration and sending. Replaces the #1891 / #1916 / #1917 chain with a single overload-based design. Protocol stays private (dispatcher RFC handles framework subclassing).
  • setRequestHandler / setNotificationHandler gain a 3-arg form: (method, { params, result? }, handler). params is any Standard Schema; the handler receives the parsed params object. _meta is stripped before validation (available as ctx.mcpReq._meta). Supplying result types the handler's return value.
  • request() and ctx.mcpReq.send gain a (req, resultSchema) overload for typed custom-method results.
Spec-method calls are unchanged (2-arg setRequestHandler, 1-arg request()). 2 overloads each on setRequestHandler/setNotificationHandler/request.
Motivation and Context
v2-main's setRequestHandler/request() only accept the closed RequestMethod/NotificationMethod unions, so vendor-prefixed methods (which the spec permits) cannot be registered or sent. The #1891/#1916/#1917 stack solved this with both v1-compat ZodSchema overloads and a ProtocolSpec<SpecT> typed-vocabulary mechanism; this PR is the minimal cut: one new overload per method. See discussion on #1891.
How Has This Been Tested?
packages/core/test/shared/customMethods.test.ts (9 tests): 3-arg registration, params validation, _meta strip, typed return via result, request() schema overload, mcpReq.send schema overload. typecheck/lint/build/docs/test:all clean locally.
Breaking Changes
None to v2-main. v1's setRequestHandler(ZodSchema, h) form is not restored here; it is mechanically codemod-able to the 3-arg form (#1950).
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
Alternative to #1891 / #1916 / #1917 (which stay open for comparison). Internally widens _requestWithSchema and the TaskManager send-chain from Zod-only AnySchema to StandardSchemaV1; Zod schemas implement StandardSchemaV1 so existing internal callers are unchanged.
Protocol is intentionally not exported in this PR. A separate dispatcher RFC (gist) covers the framework-subclassing use case; until that lands, Protocol stays internal-only.
Includes a _wrapHandler protected hook so subclass per-method validation (tools/call in Server, elicitation/create/sampling/createMessage in Client) does not require redeclaring setRequestHandler's overload set. The hook runs for both registration paths; validation behavior is unchanged.
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npm i https://pkg.pr.new/@modelcontextprotocol/client@1974

@modelcontextprotocol/server
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@modelcontextprotocol/express
npm i https://pkg.pr.new/@modelcontextprotocol/express@1974

@modelcontextprotocol/fastify
npm i https://pkg.pr.new/@modelcontextprotocol/fastify@1974

@modelcontextprotocol/hono
npm i https://pkg.pr.new/@modelcontextprotocol/hono@1974

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feat(core): custom-method support (3-arg setRequestHandler + request schema overload) by felixweinberger · Pull Request #1974 · modelcontextprotocol/typescript-sdk · GitHub
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feat(core): custom-method support (3-arg setRequestHandler + request schema overload) - #1974
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Stacks on #1976 (_wrapHandler hook refactor). Review that first.
Custom (non-spec) method support: typed registration and sending. Replaces the #1891 / #1916 / #1917 chain with a single overload-based design. Protocol stays private (dispatcher RFC handles framework subclassing).
  • setRequestHandler / setNotificationHandler gain a 3-arg form: (method, { params, result? }, handler). params is any Standard Schema; the handler receives the parsed params object. _meta is stripped before validation (available as ctx.mcpReq._meta). Supplying result types the handler's return value.
  • request() and ctx.mcpReq.send gain a (req, resultSchema) overload for typed custom-method results.
Spec-method calls are unchanged (2-arg setRequestHandler, 1-arg request()). 2 overloads each on setRequestHandler/setNotificationHandler/request.
Motivation and Context
v2-main's setRequestHandler/request() only accept the closed RequestMethod/NotificationMethod unions, so vendor-prefixed methods (which the spec permits) cannot be registered or sent. The #1891/#1916/#1917 stack solved this with both v1-compat ZodSchema overloads and a ProtocolSpec<SpecT> typed-vocabulary mechanism; this PR is the minimal cut: one new overload per method. See discussion on #1891.
How Has This Been Tested?
packages/core/test/shared/customMethods.test.ts (9 tests): 3-arg registration, params validation, _meta strip, typed return via result, request() schema overload, mcpReq.send schema overload. typecheck/lint/build/docs/test:all clean locally.
Breaking Changes
None to v2-main. v1's setRequestHandler(ZodSchema, h) form is not restored here; it is mechanically codemod-able to the 3-arg form (#1950).
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
Alternative to #1891 / #1916 / #1917 (which stay open for comparison). Internally widens _requestWithSchema and the TaskManager send-chain from Zod-only AnySchema to StandardSchemaV1; Zod schemas implement StandardSchemaV1 so existing internal callers are unchanged.
Protocol is intentionally not exported in this PR. A separate dispatcher RFC (gist) covers the framework-subclassing use case; until that lands, Protocol stays internal-only.
Includes a _wrapHandler protected hook so subclass per-method validation (tools/call in Server, elicitation/create/sampling/createMessage in Client) does not require redeclaring setRequestHandler's overload set. The hook runs for both registration paths; validation behavior is unchanged.
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🦋 Changeset detected
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LGTM, some potential nits, not blocking.
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fix: address review — assertCapability* params as RequestMethod|strin…
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