Insomnia

Insomnia is an API client and design environment covering the full cycle from specification through mocking to automated testing, built around a design first methodology where the OpenAPI specification comes before the implementation.

Design first is a genuine methodological position rather than a feature. Writing the specification first means consumers can begin building against a mock while the implementation is still being written, which removes the sequential dependency that otherwise makes every API project take as long as its slowest team.

Native API mocking is what makes that practical. Mocks generate dynamic responses configured manually or derived automatically from collections, specifications, existing responses, or plain language descriptions, so a usable fake API exists from the moment the specification does.

Testing runs unlimited collection tests with pre and post request scripting for sophisticated workflows, complex scenario validation and dynamic test data generation. AI native testing includes a native MCP client for testing MCP servers directly. Pricing starts at 0 dollars per user for Essentials, with an Enterprise tier at 45 dollars per user and annual billing saving 17 percent. Mock server usage includes 10,000 requests per month with additional capacity at 10 dollars per 25,000 requests.