In-Depth Guide to JWT Debugging & Token Security
JSON Web Tokens (JWTs) are the standard for stateless authentication in modern cloud microservices, single-page applications, and mobile apps. Our 100% private in-browser JWT Debugger lets you inspect payload claims, check expiration dates, and verify HMAC signatures without exposing sensitive access tokens to third-party logging servers.
Step-by-Step Instructions
- 1
Paste Encoded JWT
Paste your raw base64url-encoded JSON Web Token (format: header.payload.signature) or click "Load Sample" to test.
- 2
Inspect Header & Algorithm
Review the signing algorithm (e.g., HS256, RS256, ES256) and token type defined in the decoded JOSE header.
- 3
Verify Payload Claims & Expiration
Inspect issuer (iss), subject (sub), audience (aud), and human-formatted expiration (exp) and issued-at (iat) timestamps.
- 4
Verify Signature (Optional)
Enter your HMAC secret or public key to verify that the token has not been tampered with or modified in transit.
Key Features & Benefits
100% In-Browser Privacy
Zero server uploads. Your production tokens, authorization headers, and secrets remain securely in local browser memory.
Color-Coded Token Structure
Clearly visualizes the three token segments: Header (red), Payload (purple), and Cryptographic Signature (cyan).
Live Expiration Detection
Automatically converts numeric Unix exp and nbf timestamps into human-readable dates and alerts you if the token is expired.
Client-Side Signature Check
Verify HMAC-SHA256 signatures locally using the native browser Web Cryptography API without exposing secrets to third parties.
RFC 7519 Standard Compliance
Full support for standard registered claims and custom application metadata across OAuth 2.0 and OpenID Connect flows.
Instant Decoding & Validation
Zero latency: tokens are parsed instantaneously as you type or paste, with clear syntax error notifications.
Frequently Asked Questions
Is it safe to paste live production JWTs into this tool?
Yes, 100%. Traditional web token decoders often send tokens to remote web servers where they can be logged or breached. This JWT Debugger executes entirely in your browser using local JavaScript, ensuring zero network transmission of credentials.
How is a JSON Web Token structured?
A standard JWT consists of three parts separated by periods (.): the Header (specifying token type and signing algorithm), the Payload (containing user permissions, tenant ID, and expiration claims), and the Signature (used to verify authenticity).
What does the "exp" claim represent?
The "exp" (expiration time) claim identifies the exact expiration timestamp on or after which the JWT must not be accepted. It is expressed as a Unix epoch timestamp in seconds.
How do I test token verification without a production token?
Click the "Load Sample" button at the top of the tool. It populates an example token with standard claims and a preconfigured HMAC secret so you can observe live signature validation.