A JSON Web Token (JWT) is a compact, self-contained token format used to securely transmit claims between parties. JWTs are widely used in authentication and authorization systems — when you log into a web application, the server often issues a JWT that your browser sends with each subsequent request to prove your identity. A JWT consists of three Base64URL-encoded parts separated by dots: the header (algorithm and token type), the payload (claims/data), and the signature.

InfraHub's JWT Debugger decodes any JWT instantly in your browser — your sensitive tokens never leave your device.

The debugger splits the JWT on "." characters and Base64URL-decodes each segment. The header reveals the signing algorithm (HS256, RS256, ES256, etc.) and token type. The payload exposes all claims including standard ones like "exp" (expiration), "iat" (issued at), "sub" (subject), and "iss" (issuer), as well as any custom claims added by your application. Expiration status is checked against the current time and displayed prominently.

Backend developers inspect JWT payloads during API development to verify the correct claims are included. Security engineers audit JWT usage to check for weak algorithms (HS256 with short secrets), missing expiration claims, or overly permissive scopes. Frontend developers debug authentication issues by checking whether the JWT has expired or contains the expected user ID. DevOps teams validate service-to-service JWTs during microservice debugging sessions.