Interactive converter

OpenAI to Anthropic tool schema converter

Translate an OpenAI function tool to Claude strict tool use while preserving optional-field intent.

parameters → input_schemaOptionality restoredComplexity budgetStrict wrapper

Reviewed 29 August 2026Source: Anthropic strict tool use

APITC unwraps OpenAI parameters, keeps clear descriptions, normalizes object closure for strict use, and removes OpenAI-only wrapper fields.

Read the schema and its provider wrapper as one contract. APITC distinguishes target requirements from portable JSON Schema, applies mechanical repairs only when intent is recoverable, and identifies transformations that can change meaning.

Diagnostic procedure

Repair the schema, then recompile.

01
Unwrap the function
The converter accepts both Chat Completions function wrappers and Responses-style flat tools.
02
Audit optionality
Nullable-but-required OpenAI fields can become optional Anthropic fields when null was only a portability device.
03
Check complexity
APITC reports strict compilation pressure from optionals and unions.

Before

{"type":"function","name":"lookup","parameters":{"type":"object","properties":{"id":{"type":"string"}},"required":["id"],"additionalProperties":false},"strict":true}

Target-safe shape

{"name":"lookup","input_schema":{"type":"object","properties":{"id":{"type":"string"}},"required":["id"],"additionalProperties":false},"strict":true}

Interactive check

Run the schema against a real target.

Paste JSON, choose a target, and inspect the compiled shape and every portability warning before copying the result.

Contract compilerlocal browser runtime

Compile target

01 Source contract APITC canonical

02OpenAI strict

80compatibility

0 errors · 2 fixes · 0 warnings

fix$.inputSchemaClose this object

OpenAI strict requires additionalProperties: false on every object.

fix$.inputSchemaRequired array is incomplete

Strict mode requires every property in required. APITC will make limit nullable.

≈ 97 tokens compiled · input never leaves this tab

No account · no upload · no endpoint calledOpen the full tool schema compiler and operating notes →

FAQ

Before you ship

Does APITC upload my schema?

No. Parsing, diagnostics, and compilation run in your browser tab.

Is the compiled result guaranteed to preserve meaning?

Safe repairs are deterministic. When Anthropic cannot express a source constraint, APITC labels the transform as lossy instead of hiding it.

Protocol behavior checked against the Anthropic strict tool use. Recheck your pinned provider/API version before production deployment.

Repair the schema, then recompile.

Unwrap the function

Audit optionality

Check complexity

Run the schema against a real target.

Before you ship