fix(openai): apply strict fallback in the provider-path function-tool converter by AlemTuzlak · Pull Request #790 · TanStack/ai

AlemTuzlak · 2026-06-19T09:21:51Z

Follow-up to #786.

#786 added the strict:false fallback to responses-tool-converter.ts and chat-completions-tool-converter.ts, but the adapter's provider tool dispatcher (convertToolsToProviderFormat) routes MCP and function tools through a third converter — convertFunctionToolToAdapterFormat in tools/function-tool.ts — which still forced strict: true. So tools whose schema is outside OpenAI's strict subset (e.g. Notion MCP tools using $defs/oneOf) still 400'd the whole request.

This applies the same isStrictModeCompatible check there: emit strict: false and strip unsupported formats when the schema can't be expressed under strict Structured Outputs, keeping the tool callable.

Verified end-to-end: a TanStack chat() with the Notion + Linear MCP servers now completes (previously 400'd on API-get-user).

🤖 Generated with Claude Code

Summary by CodeRabbit

Release Notes

Bug Fixes
- Improved OpenAI Structured Outputs handling by automatically falling back to non-strict function definitions when a tool’s input schema isn’t fully compatible, preventing “Invalid schema” validation errors.
Tests
- Added test coverage to verify strict vs. fallback behavior based on schema compatibility, including preservation of valid schema structure and removal of unsupported format entries.

… converter The provider tool dispatcher (convertToolsToProviderFormat) routes MCP and function tools through convertFunctionToolToAdapterFormat, which still forced strict:true and 400'd on schemas outside OpenAI's strict subset (e.g. Notion MCP tools using $defs/oneOf). Apply the same isStrictModeCompatible check used by the responses/chat-completions converters: emit strict:false and strip unsupported formats when the schema can't be strict, keeping the tool callable.

coderabbitai · 2026-06-19T09:22:06Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 72f3d9d and 4158201.

📒 Files selected for processing (1)

.changeset/openai-strict-fallback-function-tool.md

✅ Files skipped from review due to trivial changes (1)

.changeset/openai-strict-fallback-function-tool.md

📝 Walkthrough

Walkthrough

convertFunctionToolToAdapterFormat gains an early compatibility guard: schemas incompatible with OpenAI's strict Structured Outputs subset (e.g., those using oneOf, $ref, $defs) now return strict: false with stripUnsupportedFormats applied, while compatible schemas continue through the existing makeStructuredOutputCompatible + strict: true path. Tests cover both branches, and release notes document the behavior.

Changes

OpenAI strict-mode fallback for function tool converter

Layer / File(s)	Summary
Compatibility guard and non-strict fallback `packages/openai-base/src/tools/function-tool.ts`	Imports `isStrictModeCompatible` and `stripUnsupportedFormats`; adds an early exit that returns `strict: false` with unsupported formats stripped when the schema cannot satisfy OpenAI's strict Structured Outputs subset; updates inline docs to describe the fallback.
Strict fallback tests `packages/openai-base/tests/tool-converter-strict-fallback.test.ts`	Adds `convertFunctionToolToAdapterFormat` import and a new test group asserting `strict: true` for compatible schemas and `strict: false` with stripped `format` fields for incompatible schemas.
Release notes `.changeset/openai-strict-fallback-function-tool.md`	Changeset documents the patch for `@tanstack/openai-base` describing the strict-to-non-strict fallback behavior in the `function-tool` converter when OpenAI strict function-calling constraints cannot be satisfied.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

TanStack/ai#786: Implements the same isStrictModeCompatible / strict: false fallback pattern in the function tool schema conversion path that this PR also adopts.

Poem

🐇 A schema walked in, full of oneOf and $ref,
The strict gate said "No!" — a potential regret.
So the rabbit stripped formats and flipped strict to false,
No 400 errors, no schema morass!
With tests to confirm both the true and the fake,
Clean tool configs bloom — what a difference we make! 🌸

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description provides context about PR `#786`, explains the gap in that fix, describes the solution applied, and includes verification details. However, it does not follow the provided template structure.	Restructure the description to follow the template: add a '## 🎯 Changes' section explaining what changed and why, and a '## ✅ Checklist' section with contributor verification steps.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: applying a strict fallback mechanism in the function-tool converter, which is the core fix for this PR.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Commit unit tests in branch fix/openai-strict-fallback-function-tool

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github-actions · 2026-06-19T09:22:47Z

🚀 Changeset Version Preview

1 package(s) bumped directly, 3 bumped as dependents.

🟩 Patch bumps

Package	Version	Reason
`@tanstack/openai-base`	0.8.6 → 0.8.7	Changeset
`@tanstack/ai-grok`	0.12.1 → 0.12.2	Dependent
`@tanstack/ai-groq`	0.4.7 → 0.4.8	Dependent
`@tanstack/ai-openai`	0.15.1 → 0.15.2	Dependent

nx-cloud · 2026-06-19T09:22:51Z

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☁️ Nx Cloud last updated this comment at 2026-06-19 12:22:32 UTC

pkg-pr-new · 2026-06-19T09:23:20Z

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commit: 4158201

…ema fix Bump @tanstack/ai-openai 0.14.4 → 0.15.2 (pins @tanstack/openai-base 0.8.7, TanStack/ai#790) and @tanstack/ai → 0.32.0. 0.8.7 emits strict:false for tool schemas outside OpenAI's strict subset in the provider-path function-tool converter, so MCP tools (e.g. Notion's API-post-search) no longer 400 — no local patch needed. Verified end-to-end against the live Slack bot.

chore: add changeset for openai strict-fallback function-tool fix
4158201

AlemTuzlak merged commit 22ccaaa into mainJun 19, 2026
10 checks passed

AlemTuzlak deleted the fix/openai-strict-fallback-function-tool branch June 19, 2026 12:29

github-actionsBot mentioned this pull request Jun 19, 2026
ci: Version Packages #791
Merged

coderabbitaiBot mentioned this pull request Jun 24, 2026
fix(openai-base): send typeless tool schemas with strict:false #833
Merged

This was referenced Jul 14, 2026
fix: preserve free-form OpenAI tool schemas #933
Merged
fix: undo strict null widening for tool inputs #939
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fix(openai): apply strict fallback in the provider-path function-tool converter - #790

fix(openai): apply strict fallback in the provider-path function-tool converter#790
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