API Debugging Tools
Free tools for debugging REST APIs, inspecting authentication tokens, formatting responses, and understanding HTTP. Everything runs in your browser — paste API responses, headers, and tokens without sending them to a third-party server.
Format raw API responses into readable JSON. Validate and detect syntax errors. Minify for request payloads. The most-used API debugging tool.
Decode JWT tokens to inspect claims, expiration, and header algorithm. See if a token is expired. Essential for debugging auth flows.
Convert cURL commands to JavaScript fetch() calls or Axios requests. Paste from browser DevTools and get working JS code.
Complete HTTP status code reference — 1xx informational, 2xx success, 3xx redirects, 4xx client errors, 5xx server errors — with explanations.
Inspect and analyze HTTP request and response headers. Understand security headers like CORS, CSP, HSTS, and caching directives.
Encode query parameters with encodeURIComponent or decode percent-encoded URLs. Handles Unicode, spaces, and all special characters.
Encode and decode Base64 — used in Basic Auth headers, JSON binary payloads, and data URIs. Also handles Base64URL for JWTs.
Validate OpenAPI 3.x and Swagger 2.0 specifications. Catches schema errors, missing fields, and invalid references before deployment.
Convert between XML and JSON formats instantly. Useful for working with legacy SOAP APIs, RSS feeds, and config files.
Preview HTML email templates in desktop and mobile viewports side by side. Test template variable substitution before sending.
Audit and clean your HTML <head> tags. Identifies duplicate tags, missing canonical, and OG tag issues.
API debugging workflow
A typical API debugging session involves: copying a response from browser DevTools or Postman, pasting it into a formatter to read it, decoding a JWT from the Authorization header to check claims and expiration, and verifying that query parameters are correctly URL-encoded. These tools cover every step of that workflow without requiring an account or uploading anything. For HTTP specification details, see the MDN HTTP reference.