Gesso is a PHP library that enables provider-side OpenAPI contract testing. It allows developers to write tests that validate live HTTP requests and responses against an OpenAPI schema using PHPUnit or Symfony WebTestCase. The tool ensures API implementations do not drift from their published specifications and supports features such as schema-driven fuzzing and PSR-7 validation.
Gesso sits in PulseGate's Testing & QA category. It focuses on verifying that a Symfony or PHP API implementation still matches its published OpenAPI specification. Gesso is an open-source project aimed at php developers. The project is open source (MIT). Gesso is available on API.
Studio Design builds and maintains Gesso, and the product first shipped in 2026. The project is developed in the open on GitHub with 220 commits in the last 90 days. Among its 4 catalogued features are OpenAPI Contract Testing, PHPUnit Integration, and Symfony Support. It exposes integrations via a public API.
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Contract testing a Symfony API with OpenAPI verified by the PulseGate indexer
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