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Schemathesis

schemathesis.io

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Spec score 7.5 #16 of 26 in Fuzz Testing Software

What it is

Schemathesis generates property-based tests from OpenAPI and GraphQL schemas to help engineers find API bugs. Its cases probe boundary values, type mismatches and constraint violations, and it validates API responses against the OpenAPI specification. For multi-step workflows, it chains operations using links inferred from a schema. During a run, it can learn validation rules, resource IDs and authentication requirements from server responses, then reuse them. Users can add Python checks for business rules alongside built-in checks. It supports OpenAPI 2.0, 3.0, 3.1 and 3.2, plus GraphQL schemas. Authentication options include Bearer tokens, Basic authentication and API keys, with environment variable substitution and Python hooks for dynamic flows. Integrations include a GitHub Action, Docker image, pip or uvx installation, and pytest. Reports can be exported as JUnit, VCR, HAR, NDJSON, JSON or Allure; failures can also be saved with curl commands for replay. The tool is self-hosted and licensed under MIT.

Spec sheet

Purpose
Schemathesis generates property-based tests from OpenAPI and GraphQL schemas to find API bugs.Read 4 Oct 2026 · schemathesis.io
Intended users
The maker presents Schemathesis for engineers testing OpenAPI or GraphQL APIs and integrating API tests into CI/CD.Read 4 Oct 2026 · schemathesis.io
Integrations
The maker lists a GitHub Action, Docker image, pip or uvx installation, and pytest integration.Read 4 Oct 2026 · schemathesis.io
Support
The maker directs users to Discord for technical support, configuration questions, bug reports, and integration examples.Read 4 Oct 2026 · schemathesis.io
License
The project repository states that Schemathesis is licensed under the MIT license.Read 4 Oct 2026 · github.com
Adaptive testing
During a run, it learns from server responses and reuses discovered validation rules, resource IDs, and authentication requirements.Read 4 Oct 2026 · schemathesis.io
Authentication
It supports Bearer tokens, Basic authentication, and API keys, with environment variable substitution and Python hooks for dynamic flows.Read 4 Oct 2026 · schemathesis.io
Custom checks
Users can add Python checks for business rules alongside built-in checks.Read 4 Oct 2026 · schemathesis.io
Reports
It can export JUnit, VCR, HAR, NDJSON, JSON, and Allure reports, and save failures with curl commands for replay.Read 4 Oct 2026 · schemathesis.io
Response validation
It validates API responses against the OpenAPI specification.Read 4 Oct 2026 · schemathesis.io
Security and privacy
The privacy policy says the company uses commercially acceptable means to protect personal data but cannot guarantee absolute security.Read 4 Oct 2026 · schemathesis.io
Specifications
It supports OpenAPI 2.0, 3.0, 3.1, and 3.2, plus GraphQL schemas.Read 4 Oct 2026 · schemathesis.io
Stateful testing
It chains API operations into multi-step workflows using links inferred from the schema.Read 4 Oct 2026 · schemathesis.io
Test generation
It generates cases that probe boundary values, type mismatches, and constraint violations.Read 4 Oct 2026 · schemathesis.io

Plans and prices

Schemathesis Free Open-source API testing tool; generates tests from OpenAPI and GraphQL schemas Read 4 Oct 2026 · schemathesis.io

Every Schemathesis plan and price →

Strong points and limits

Strong points

  • Generates tests for OpenAPI and GraphQL schemas.
  • Validates responses against OpenAPI specifications.
  • Chains operations into multi-step workflows.
  • Integrates with GitHub Actions, Docker and pytest.
  • Exports reports in six listed formats.

Limits

  • The deployment model is self-hosted.
  • Custom business-rule checks use Python.

Who it suits

Schemathesis suits engineers testing OpenAPI or GraphQL APIs, especially those integrating API tests into CI/CD. Its Python checks and multiple installation and reporting options support customizable test workflows.

Verdict

Schemathesis combines schema-driven test generation with response validation and stateful workflows. It is a free, MIT-licensed option for teams prepared to run a self-hosted tool.

Where Specifiction places it

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