fix(ai-openrouter): keep optional tool fields optional - #1545
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tombeckenham merged 8 commits intoOct 4, 2026
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The Chat Completions adapter sent function tools without `strict`. OpenRouter serves OpenAI models through the upstream Responses API, where an omitted `strict` normalizes the schema to strict mode, so the model had to fill every optional field. Send `strict: false`, matching the schema the adapter sends as authored. The Responses adapter sends strict, null-widened tool schemas but emitted the model's `null` for an omitted optional unchanged, so the tool's `.optional()` validation failed and `execute` never ran. Strip exactly the nulls the strict conversion added before emitting TOOL_CALL_END. Fixes TanStack#1542
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Included review availability: This review used your included allowance. Your plan provides up to 8 included reviews per hour; 7 remain after this review. 📝 WalkthroughWalkthroughThe OpenRouter Chat Completions adapter now sends function tools with ChangesOpenRouter optional tool fields
Priority: ➖ Normal Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Bug fix · Severity of issue fixed: Medium Sequence Diagram(s)sequenceDiagram
participant Chat as Chat Completions adapter
participant Router as OpenRouter
participant Tool as Tool execution
Chat->>Router: Send function tool with strict false
Router->>Tool: Return tool arguments without omitted optional field
sequenceDiagram
participant Responses as Responses adapter
participant Router as OpenRouter
participant Normalizer as Tool-input normalizer
participant Tool as Tool execution
Responses->>Router: Send strict tool schema
Router->>Responses: Return arguments with conversion-added null
Responses->>Normalizer: Normalize arguments using tool schema
Normalizer->>Responses: Return input without widened nulls
Responses->>Tool: Emit normalized tool input
Suggested reviewers: Merge Risk: ⚪ Minimal · up to The change improves optional-field handling for OpenRouter tool calls. The remaining multi-variant anyOf limitation predates this change, and no new merge-blocking behavior is established. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to The change restores the distinction between omitted optional values and explicit nulls. The added test endpoint uses simulated responses, a dummy credential, and an in-memory callback. No security regression was established, but validation across all supported schema forms and externally hosted test deployments remains unconfirmed. Retained concerns Security review detailsSecurity Blast Radius
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Review comments at
@packages/ai-openrouter/src/internal/responses-tool-converter.ts:
- Around line 100-120: Update diffNullWidening to retain child maps separately
for each non-null variant when an anyOf has multiple variants, then update
undoNullWidening to apply only the map belonging to the matching variant. Do not
merge variant maps, so legitimate nullable values in other variants remain
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.changeset/openrouter-optional-tool-fields.mdpackages/ai-openrouter/src/adapters/responses-text.tspackages/ai-openrouter/src/internal/responses-tool-converter.tspackages/ai-openrouter/src/tools/function-tool.tspackages/ai-openrouter/tests/openrouter-adapter.test.tspackages/ai-openrouter/tests/openrouter-responses-adapter.test.tstesting/e2e/src/routeTree.gen.tstesting/e2e/src/routes/api.openrouter-strict-tool-optionals.tstesting/e2e/tests/openrouter-strict-tool-optionals.spec.ts
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…ct-tool-optionals # Conflicts: # testing/e2e/src/routeTree.gen.ts
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…ting claim Merge the two null-widening unit tests into one table-driven test that delivers the arguments through function_call_arguments.done, the output_item.done backfill, and the response.completed backfill. State the upstream strict behaviour as observed (TanStack#1542) in one place, and note the multi-shape union limit in the changeset. Refs TanStack#1542
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Thanks for this. Approving
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Btw I debated if this was the right fix. I'm still not sure that passing strict: false is the right call, but looking through all the options, I think this is the best way to handle it. |
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Fair point, thanks for the transparency 🙏 |
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With an OpenAI model, an
.optional()tool field breaks on both OpenRouter text adapters. On Chat Completions the model cannot leave the field out. On Responses the tool never runs when the model leaves it out. This PR sendsstrict: falseon Chat Completions and removes the provider-addednullon Responses.🎯 Changes
Fixes #1542
createOpenRouterTextnow sends each function tool withstrict: false. The schema still goes out as written.createOpenRouterResponsesTextremoves thenulls that its strict conversion added. It does this before it emitsTOOL_CALL_END, on all three emit paths (function_call_arguments.doneand theoutput_item.doneandresponse.completedbackfills). A.nullable()field keepsnull.nulls comes from a diff of the original schema against the wire schema. So it stays aligned with a subclassmakeStructuredOutputCompatibleoverride. It also goes into a.nullable()object (anyOf: [object, null]).strict: false. One table test for the null undo, with one row for each of the three emit paths. An E2E spec drives both adapters through the real SDK with a stubbed fetch.No docs change.
docs/tools/tools.mdalready states the contract this restores: an omitted.optional()tool field is absent when the tool runs, and a.nullable()field keepsnull.✅ Checklist
pnpm run test:pr, or these tests do not apply to this pull request.docs/for this change, or this change is not user-facing.pnpm changeset), or this PR does not change a published package.🚀 Release Impact
Root cause
Issue. With an OpenAI model, the OpenRouter adapters break
.optional()tool fields. On Chat Completions the model always fills them and makes up values like[""]formin(1)arrays. On Responses,executenever runs when the model leaves a field out.Cause.
convertFunctionToolToAdapterFormatsends nostrict. OpenRouter serves OpenAI models through the upstream Responses API (seedebug.echo_upstream_body). There, an omittedstrictnormalizes the schema to strict mode, so every field becomes required.convertFunctionToolToResponsesFormatwidens optionals to required + nullable itself, butprocessStreamChunksemits the model'snullunchanged. The engine then checks thatnullagainst.optional(), which rejects it.Fix. Chat Completions says
strict: false, which matches the schema it sends as written. Responses undoes its own widening beforeTOOL_CALL_END, the same wayopenai-basedoes since #939.Possible alternatives
openai-base. Widen compatible schemas, sendstrict: true, and undo the widening. OpenRouter also routes to non-OpenAI providers, andstrict: falseis valid for all of them. Tested with Claude on Bedrock and Gemini on Vertex.strict: falseon Responses. This is a smaller diff. But it removes the strict mode that the Responses adapter turns on for every tool on purpose.nulls in the engine for every adapter. The engine does not know whichnulls strict mode added, so it would also drop a genuine.nullable()null.Testing
Commands run (Node 24):
pnpm run test:pr— passedpnpm --filter @tanstack/ai-e2e test:e2e -- tests/openrouter-strict-tool-optionals.spec.ts— 2 passed. Both fail with the fix commit reverted.mainand pass on this branch.pnpm --filter @tanstack/ai-e2e test:e2e— 415 passed, 16 failed. All openrouter specs pass. The failures are browser UI timeouts in specs that do not use OpenRouter (middleware, lazy tools, tool approval, continuations). The 4middleware.spec.tsfailures happen the same way onmain(62bec34b). I did not check the other 12 onmainone by one.df4fff538(tests and comments only, on top of the merge ofmainat632fd806):nx run-many -t test:lib,test:types,test:oxlint -p @tanstack/ai-openrouterpassed, 247 tests. With the null undo turned off at one emit path, only the row for that path fails.pnpm run test:prand the E2E suite did not run again on this commit.A separate repro test was not added to the branch. It ran on a clean
mainworktree (62bec34b) and on this branch:Manual test (with an OpenRouter key):
live.mjssnippet from OpenRouter adapters: optional tool fields cannot be omitted (Chat Completions) or fail validation (Responses) #1542 againstopenai/gpt-5.5. Withoutstrict, the model sendsstrings. Withstrict: false, it leavesstringsout.main. It printsInput validation failed … expected object, received null.executeruns with{ guitar: 'Martin D-28' }.How this PR makes testing easy:
tests/openrouter-adapter.test.ts,tests/openrouter-responses-adapter.test.ts, andtesting/e2e/tests/openrouter-strict-tool-optionals.spec.ts.Risk / rollback
Low. Chat Completions tools with a schema that the model already filled completely behave the same way. OpenAI models are no longer held to the schema by constrained decoding on Chat Completions. The engine still checks every tool input against the tool's schema. Revert the PR to undo.
Known limit: the Responses adapter does not remove the
nullfor an optional field inside a union of several object shapes. That tool input still fails validation, the same as onmain. The changeset states this.Not in this PR: the OpenRouter strict converter adds
nulltotypebut not toenumorconst, so an optional enum still cannot benullon the Responses wire.openai-basehandles that case. I can follow up.Summary by CodeRabbit
nullvalues added for optional fields that weren’t provided, including within nested objects.null.