yapi

YApi is a self-hosted API management platform aimed at helping development teams, product managers, and QA (quality assurance) testers collaborate more effectively around APIs. An API (Application Programming Interface) is the technical "contract" between a frontend (what users see) and a backend (the server logic) — defining how they communicate. Managing these contracts in a shared, visual tool avoids confusion about what data gets sent and received.

YApi provides a browser-based interface where teams can create, publish, and maintain API documentation. It includes a built-in mock server — a fake backend that returns realistic-looking test data — so frontend developers can start building before the real backend is ready. There is also an API debugging tool similar to Postman (a popular API testing app), letting you send test requests directly from the interface. Automated testing with response assertions is supported, and the platform can import API definitions from formats like Swagger/OpenAPI, HAR, and Postman collections.

Permissions are managed in a flat hierarchy that balances control for large enterprise projects with ease of use. The platform is free, open-source, and designed to be deployed internally on your own network so that sensitive API details never leave your company.

It runs on Node.js with a MongoDB database and is written in JavaScript. You would use YApi if your team needs a private, centralized place to document, test, and mock your APIs without relying on external services.