JWT Decoder

What is JWT Decoder?

A JWT (JSON Web Token) decoder parses and displays the contents of a JWT without needing the secret key. JWTs are the standard authentication token format used by OAuth 2.0, OpenID Connect, and most modern web APIs. They consist of three Base64-encoded parts: a header (algorithm and type), a payload (claims like user ID, roles, expiration time), and a signature. This tool lets you inspect any JWT to see its claims, check expiration times, verify the algorithm, and debug authentication issues — all without server access.

How It Works

Paste a JWT string and the tool splits it on the two period (.) delimiters into header, payload, and signature. It Base64URL-decodes the header and payload sections, then parses the resulting JSON. The decoded data is displayed with proper formatting. Timestamp claims (iat, exp, nbf) are converted to human-readable dates so you can instantly see when the token was issued, when it expires, and whether it's currently valid. The signature portion is displayed but cannot be verified without the secret key.

Common Use Cases

• •Debugging authentication failures by inspecting token claims and expiration times
• •Verifying that login flows issue tokens with the correct user roles and permissions
• •Checking token expiration to understand why API calls return 401 Unauthorized
• •Inspecting third-party OAuth tokens to understand what claims and scopes are included
• •Debugging SSO (Single Sign-On) issues by examining identity provider tokens
• •Verifying token structure during API development and integration testing

Frequently Asked Questions

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