OpenAPI Stub from JSON

What this tool does

Paste sample request and response JSON and this tool generates a complete OpenAPI 3.1 path-and-operation stub. It infers JSON Schema from the samples, wires those schemas into requestBody and responses, adds path and query parameters, and can emit YAML or JSON for pasting into a larger spec.

It is designed for the early documentation step: you have example payloads from a client, a test fixture, a log, or a prototype, and you want a deterministic OpenAPI starting point instead of an empty path block.

It can generate:

• request and response body schemas from JSON objects, arrays, scalars, and nulls;
• required lists based on observed object keys;
• string formats such as email, URI, UUID, date, date-time, and IPv4;
• component schemas plus $ref, or inline schemas;
• path parameters from /things/{thingId} and typed query parameters from a sample query string;
• optional bearer, basic, or X-API-Key security boilerplate;
• optional generic 400 and 500 error responses.

Worked example

Use this request:

{"name":"Ada Lovelace","email":"[email protected]","active":true}

and this response:

{"id":7,"name":"Ada Lovelace","email":"[email protected]","created_at":"2026-08-21T07:00:00Z"}

with Method: POST, Path: /users, and Operation ID: createUser. The YAML output includes a path operation like:

openapi: 3.1.0
paths:
  /users:
    post:
      operationId: createUser
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateUserRequest'

The generated component schemas infer email as a formatted string, active as boolean, id as integer, and created_at as date-time. Review the descriptions, validation rules, enum choices, headers, and auth scopes before publishing the spec.

Limits and edge cases

• This generates one operation per run. Use it repeatedly for multiple endpoints, or use a HAR-to-OpenAPI workflow when you have a whole captured session.
• A sample can only show what it contains. It cannot infer enums, minimum/maximum values, regex patterns, length limits, auth scopes, headers, pagination semantics, or business descriptions.
• Empty arrays become arrays with unconstrained item schemas; null values become OpenAPI 3.1 JSON Schema null types but do not reveal the intended non-null type.
• Array-of-object samples are merged across every element. Keys present in every object stay required; keys seen only in some elements become optional.
• The output is a stub. Treat it as a structured first draft, then edit names, summaries, descriptions, examples, response coverage, and validation constraints.

FAQ