JWT Decoder

JSON Web Tokens (JWTs) are the backbone of modern web authentication. Used in OAuth 2.0, OpenID Connect, and countless API authentication schemes, JWTs carry encoded claims about users, sessions, and permissions. As a developer, you frequently need to inspect JWT contents during development — checking expiration times, verifying role claims, debugging authentication failures, or inspecting tokens received from third-party identity providers.

The problem is that most online JWT decoders require you to paste your token into a web form that sends it to a backend server for decoding. This is a massive security risk. JWTs often contain production access tokens, refresh tokens, or API keys that could be used to impersonate users, access protected resources, or compromise entire authentication systems. Pasting these tokens into a third-party website is equivalent to handing your house keys to a stranger.

Our JWT Decoder runs 100% offline in your browser. The moment the page loads, the tool is fully functional with zero dependencies on external servers. When you paste a JWT, it is split into its three Base64URL-encoded parts (header, payload, signature), decoded using the browser's native atob() function, parsed as JSON, and displayed in a formatted, syntax-highlighted view. At no point during this process is any data transmitted over the network. You can verify this by opening your browser's Network tab in DevTools — you will see zero outbound requests while decoding tokens.

The tool displays the complete header (showing the algorithm and token type), the full payload (with all standard and custom claims), and the raw signature (as a Base64-encoded string). Standard claims like exp (expiration), iat (issued at), nbf (not before), sub (subject), iss (issuer), and aud (audience) are clearly labeled and formatted. Timestamp claims are automatically converted to human-readable dates for easy debugging.