You Don't Have an OpenAPI Spec? That's Fine.
Zero-Spec extraction reads your FastAPI, Express, or NestJS source code and generates an OpenAPI spec automatically.
The number one reason teams don't check for breaking API changes: they don't have an OpenAPI spec. The API exists in code but nobody wrote the spec file.
Zero-Spec extraction solves this. Point it at your source code and it generates an OpenAPI spec by reading your route definitions, decorators, and type annotations.
Supported frameworks
FastAPI
Reads @app.get, @app.post decorators, Pydantic models, and type hints. Generates OpenAPI 3.1.
Express
Reads app.get(), router.post() calls and extracts paths, methods, and parameters. Generates OpenAPI 3.0.
NestJS
Reads @Controller, @Get, @ApiProperty decorators and DTO classes. Generates OpenAPI 3.0.
How to use it
# Generate a spec from your source code npx delimit-cli zero-spec ./src # Then use it with the GitHub Action # or diff it against a previous version npx delimit-cli diff old-api.yaml generated-api.yaml
The generated spec won't be perfect -- it's a starting point. But it's enough to start tracking changes. Once you have a spec checked into git, Delimit can diff it on every PR and catch breaking changes before they merge.
You don't need a complete spec to get value. Even a skeleton with paths and methods is enough to detect removals and additions.
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npx delimit-cli setupRead the quickstart