A comprehensive guide to RESTful API design principles

Voiden.md is an offline-first, Git-native API workspace that unifies specs, docs, tests, and mocks using programmable Markdown blocks. Build APIs the way you actually work.

Mailpit is a free, open-source SMTP testing tool built with Go and Vue. It provides a modern web UI for viewing and testing emails, and includes a REST API for integration testing.

Tests an OpenAPI based on invariants.