What Is API Tester?

API Tester is a free, web-based HTTP client for testing REST APIs and GraphQL endpoints. Think of it as a lightweight alternative to Postman or Insomnia that runs entirely in your browser — no download or account required.

REST Features

• All HTTP methods: GET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS
• Custom headers with enable/disable toggles
• Query parameter builder
• Raw JSON body or file uploads (multipart/form-data)
• Response viewer with JSON tree, raw text, and headers tabs
• Status code, response time, and size at a glance

GraphQL Features

• Query and mutation editor
• Variables panel with JSON input
• File upload fields (GraphQL multipart upload spec)
• Schema introspection explorer with queries, mutations, and types
• SSE and WebSocket subscription support

Shared Features

• Request history stored locally (up to 20 entries per mode)
• Click-to-replay from history
• Collapsible JSON tree viewer with color-coded types
• Works entirely in the browser with no backend proxy