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JWT Decoder

Decode and inspect JWT tokens. View header, payload, and verify signature.

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Frequently Asked Questions

What is a JWT token?
A JSON Web Token (JWT) is a compact, URL-safe token format used for securely transmitting information between parties. It consists of three parts: header, payload, and signature, separated by dots.
Is it safe to decode JWTs here?
Yes! Decoding happens entirely in your browser. No tokens are sent to any server. However, never share your JWTs publicly as they may contain sensitive information.
Can this tool verify JWT signatures?
This tool decodes the token to show its contents but does not verify the cryptographic signature. Signature verification requires the secret key or public key.
What are the three parts of a JWT?
A JWT consists of three Base64URL-encoded parts separated by dots: the header (specifying the algorithm and token type), the payload (containing claims like user ID, roles, and expiration), and the signature (a cryptographic hash that verifies the token has not been tampered with).
What are common JWT claims?
Standard claims include: iss (issuer), sub (subject), aud (audience), exp (expiration time), nbf (not before), iat (issued at), and jti (JWT ID). Applications also add custom claims like user roles, permissions, and email addresses.
How do I check if a JWT has expired?
Our decoder displays the "exp" (expiration) claim as a human-readable date and time, along with a clear indicator of whether the token is currently expired. This makes it easy to diagnose authentication issues caused by stale tokens.
What algorithms are used in JWTs?
The most common algorithms are HS256 (HMAC with SHA-256, using a shared secret), RS256 (RSA with SHA-256, using public/private key pairs), and ES256 (ECDSA with SHA-256). The algorithm is specified in the JWT header and determines how the signature is created and verified.
Why should I never share a JWT publicly?
JWTs often contain sensitive information like user IDs, email addresses, roles, and permissions. While the payload is only Base64-encoded (not encrypted), the signature allows the holder to authenticate as that user. Sharing a valid JWT is essentially sharing your session credentials.

How to Use the JWT Decoder

Paste a JSON Web Token into the input field and the decoder instantly parses it into its three components: header, payload, and signature. The header reveals the signing algorithm and token type. The payload displays all claims in a formatted, easy-to-read JSON structure, with timestamps automatically converted to human-readable dates. Expiration status is highlighted so you can immediately see whether the token is still valid. Everything runs in your browser, and no token data is ever sent to a server.

This tool is invaluable during development and debugging. Instead of manually Base64-decoding each segment or writing custom scripts, you get a complete, formatted breakdown of any JWT in seconds. Simply paste, inspect, and continue your work.

What Is a JSON Web Token (JWT)?

A JSON Web Token is an open standard (RFC 7519) that defines a compact, self-contained format for securely transmitting information between parties as a JSON object. JWTs are widely used for authentication and authorization in modern web applications, APIs, and microservices architectures. When a user logs in, the server issues a JWT that the client includes in subsequent requests to prove identity and permissions.

Each JWT contains three Base64URL-encoded segments separated by dots. The header specifies the signing algorithm (such as HS256 or RS256) and the token type. The payload carries claims, which are statements about the user and additional metadata like expiration time, issuer, and audience. The signature is a cryptographic hash that allows the receiving party to verify the token has not been altered. This self-contained design eliminates the need for server-side session storage, making JWTs ideal for stateless, scalable architectures.

JWT Decoder Use Cases

Backend developers decode JWTs to debug authentication flows, verify that the correct claims are present, and check token expiration during development. Front-end developers inspect tokens stored in localStorage or cookies to understand the user context their application is receiving. API developers decode tokens sent in authorization headers to troubleshoot access-denied errors and role-based permission issues.

Security engineers audit JWTs to check for weak algorithms (like "none"), overly broad permissions, or excessively long expiration periods. QA testers decode tokens to verify that login and token-refresh flows produce the expected claims. DevOps engineers inspect tokens in CI/CD pipelines and service-to-service authentication to diagnose integration failures. The decoder makes all of these tasks faster by providing instant, structured visibility into token contents.

Why Use Our JWT Decoder?

Our JWT Decoder is designed for speed, privacy, and clarity. All decoding happens client-side in your browser, meaning sensitive tokens are never transmitted to any server. The interface provides clean JSON formatting with syntax highlighting, automatic timestamp conversion, and expiration status indicators that make it easy to spot issues at a glance. Unlike command-line tools that require piping through base64 and jq, our tool gives you a complete token breakdown in a single paste. It is free, requires no account, and works from any device, making it the most convenient way to inspect JWTs during development and debugging.

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