JWT Decoder & Validator
Free online JWT decoder for developers. Decode and validate JSON Web Tokens instantly in your browser. No signup, privacy-focused, client-side processing.
Security Notice
Never share your secret keys with untrusted parties. While this tool processes data entirely in your browser for privacy, be cautious when using the share feature with JWT tokens containing sensitive information. The share button encodes the token in the URL, which could expose your data if shared publicly. Only share decoded tokens in development/testing environments with trusted team members.
How to Use This JWT Decoder
Using our JWT decoder is simple and instant. Paste your JWT token into the input field at the top, and it will automatically decode in real-time as you type. The tool splits the token into three components: the header (containing the algorithm and token type), the payload (containing your claims and data), and the signature (the cryptographic signature used for verification).
The decoder automatically checks token expiration based on the "exp" claim in the payload, displaying how long until expiration or how long ago it expired. If you have the secret key used to sign the token, you can verify the signature by entering the secret in the verification section – this works for HMAC algorithms (HS256, HS384, HS512). RSA signatures require public keys and are not supported in browser-based verification.
All decoding happens entirely in your browser using pure JavaScript. Your tokens never leave your device, ensuring complete privacy and security. You can copy individual components, download the full decoded JWT as JSON, save tokens to your local history, or share a link with the token state. Perfect for debugging authentication issues or understanding JWT structure.
Common Use Cases for JWT Decoding
JWT (JSON Web Token) is the industry standard for secure authentication and authorization in modern web applications and APIs. Developers use JWTs to transmit user identity and claims between systems in a compact, self-contained format. When building or debugging applications that use JWT authentication, you frequently need to inspect token contents to verify claims, check expiration times, or troubleshoot authentication failures.
Common scenarios include debugging API authentication errors, validating tokens received from OAuth providers, inspecting tokens in browser cookies or local storage, verifying user roles and permissions stored in token claims, and checking why authentication is failing (often due to expired tokens). Security teams also use JWT decoders during penetration testing to analyze token structure and identify potential vulnerabilities.
This tool is invaluable for full-stack developers implementing authentication systems, DevOps engineers troubleshooting API gateway issues, security researchers analyzing token-based authentication, and anyone learning how JWT authentication works. The real-time decoding and signature verification features make it easy to understand and debug JWT-based systems.
Why Use Our JWT Decoder?
Privacy First
Your JWT tokens never leave your browser. All decoding and verification happens client-side using pure JavaScript, ensuring complete privacy and security for sensitive authentication tokens.
Lightning Fast
Instant real-time decoding as you type. Automatic expiration checking and support for signature verification. Works offline once the page is loaded.
Reliable & Free
No signup, no payment, no limitations – completely free forever. Built with Web Crypto API for secure HMAC signature verification.
Need more developer tools? Check out textdiff.io for additional data validation and conversion utilities.
Frequently Asked Questions
What is a JWT token?
JWT (JSON Web Token) is a compact, URL-safe token format used for securely transmitting information between parties. It consists of three parts: header (algorithm and token type), payload (claims and user data), and signature (cryptographic verification). JWTs are commonly used for authentication and authorization in modern web applications and APIs.
Is it safe to decode my JWT tokens here?
Yes, absolutely. All decoding happens entirely in your browser using JavaScript. Your tokens never leave your device or get sent to any server. However, be cautious with the share feature – it encodes the token in the URL, which could expose sensitive data if shared publicly. Only use share in development/testing with trusted team members.
Can this tool verify JWT signatures?
Yes, but with limitations. The tool can verify HMAC signatures (HS256, HS384, HS512) if you have the secret key. RSA and ECDSA signatures require public keys and cannot be verified in a browser-based tool due to security constraints. For production signature verification, use server-side libraries.
What does the expiration check do?
The tool automatically checks the "exp" claim in the JWT payload, which contains the token's expiration timestamp. It displays how long until expiration (for valid tokens) or how long ago it expired (for expired tokens). This helps quickly identify authentication issues caused by expired tokens.
Can I save my decoded tokens?
Yes, you can save tokens to your browser's local history using the "Save to History" button. All history is stored locally in IndexedDB and never leaves your device. You can view, restore, and delete history entries at any time. This is useful for comparing tokens or quickly accessing frequently used test tokens.
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