RESTler

RESTler is a stateful REST API fuzzing tool by Microsoft that automatically tests cloud services through their REST APIs to find security and reliability bugs.

For a service with an OpenAPI (Swagger) specification, RESTler analyses the whole specification, infers producer-consumer dependencies among request types, and generates and executes tests through the API. During testing it checks for specific classes of bugs and learns from previous responses how the service behaves, which lets it explore deeper into the service.

RESTler is distributed under the MIT licence on GitHub; the last change dates from June 2026.