OpenAPI to Function Calling

🔒 Processed 100% in your browser — nothing is uploaded

About this tool

Connecting an LLM to your API usually starts with a tedious translation job: turning an OpenAPI specification into the function-calling schema that OpenAI or Anthropic expects. This converter automates it. Paste an OpenAPI 3 document in JSON or YAML, and the tool walks every path and operation, extracts the operationId, summary and description, merges path-level and operation-level parameters, resolves simple $ref pointers, and folds request bodies into a single JSON Schema of properties. You can then export the result in OpenAI tools format — an array of type function objects with name, description and parameters — or in Anthropic tool-use format with input_schema. Operations without an operationId get a readable generated name, and you can filter to specific tags before converting. Everything runs client-side, so internal or unreleased API specifications stay on your machine. Use it to bootstrap an agent that calls your REST API, to prototype tool-use demos, or to sanity-check that your spec documents parameters well enough for a model to call them correctly.

How to use OpenAPI to Function Calling

  1. Paste your OpenAPI 3 specification (JSON or YAML) into the input area.
  2. Choose the target format: OpenAI tools or Anthropic tools.
  3. Press Convert to generate the function-calling schema.
  4. Copy the resulting JSON array and paste it into your API request as the tools parameter.

Frequently asked questions

Which OpenAPI versions are supported?

OpenAPI 3.x documents in JSON or YAML. Swagger 2.0 files must be upgraded first, for example with the official swagger-converter.

How are request bodies handled?

The properties of an application/json request body are merged into the function parameters schema, alongside query, path and header parameters.

Are $ref references resolved?

Local component references such as #/components/schemas/Pet are resolved inline. External file references are not fetched.

Is my API spec uploaded anywhere?

No. Parsing and conversion happen locally in your browser, which makes the tool safe for private or pre-release specifications.

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