Schemathesis
Property-based fuzzing that generates API tests straight from your OpenAPI schema.
What it is
Schemathesis reads an OpenAPI or GraphQL schema and generates thousands of valid and deliberately hostile requests, checking that responses conform to the schema and that the server never returns an unhandled 500. It routinely finds edge cases no hand-written test would cover, for the cost of pointing it at a spec.
Best for
Where it is strong
- Enormous coverage for almost no authoring effort — the schema is the test suite.
- Reliably finds unhandled server errors and schema violations that manual tests miss.
- Failures come with a minimal reproducing case.
Where it falls short
- Only as good as your schema; a vague or inaccurate spec produces noise.
- Tests conformance, not business correctness — it cannot know a discount was miscalculated.
- Generated failures can be tedious to triage at first.
Pricing
Free tier available
Free tierFree tier: The CLI and Python library are open source and free.
What drives the bill: Open source. A commercial hosted service exists for reporting and continuous runs.
Check current pricing on Schemathesis’s siteFigures are indicative and were last reviewed August 2026. Vendors change pricing often; confirm before you commit.
Works with
What people who use Schemathesis say
No reviews of Schemathesis yet. If you have used it in anger, yours would be the first.
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