What is JWT Decoder?
The JWT Decoder is a free, browser-based tool that parses JSON Web Tokens (JWTs) as defined by RFC 7519 and displays their constituent parts — the header, payload, and signature — in a readable, color-coded format. JWTs are the backbone of modern authentication and authorization systems, used by OAuth 2.0, OpenID Connect, and countless API platforms to securely transmit claims between parties. A JWT consists of three Base64URL-encoded segments separated by dots. This tool decodes each segment, pretty-prints the JSON, highlights registered claims like 'exp' (expiration), 'iat' (issued at), and 'sub' (subject), and converts Unix timestamps to human-readable dates so you can quickly assess whether a token is still valid.
Why Use JWT Decoder?
Debugging authentication issues often starts with inspecting the token. Is it expired? Does it contain the right scopes? Is the audience claim correct? Manually decoding Base64URL strings and converting epoch timestamps is slow and error-prone. This tool gives you a complete token breakdown in one click. Unlike server-based JWT decoders, this tool processes everything locally in your browser, ensuring that sensitive access tokens, refresh tokens, and ID tokens are never transmitted over the network. It is indispensable for backend developers building auth flows, frontend developers handling token storage, and QA engineers verifying token claims during testing.
How to Use
Paste the complete JWT string (all three dot-separated parts) into the input field. The tool instantly decodes the header and payload, displaying the algorithm (e.g., RS256, HS256), token type, issuer, subject, audience, expiration, and all custom claims. Timestamps are shown in both Unix epoch and local date-time format. If the token is expired, a prominent warning badge appears. You can also paste just the header or payload segment if you only need to decode a specific part. For signature verification, provide the signing secret (HMAC) or public key (RSA/ECDSA) in the optional verification panel.
Example Usage
You are troubleshooting a 401 Unauthorized error from your API. Paste the JWT from the Authorization header: eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWUsImV4cCI6MTYxNjIzOTAyMn0.signature. The decoder reveals that the 'exp' claim is 1616239022 (March 20, 2021), confirming the token expired years ago. The 'admin' claim is set to true, which you can verify against your expected authorization rules. The header shows RS256, telling you the API uses RSA asymmetric signing.
Benefits
Instant, client-side decoding keeps your tokens confidential. Human-readable timestamp conversion eliminates manual epoch math. Color-coded sections make it easy to distinguish header, payload, and signature at a glance. Expiration warnings catch stale tokens immediately. Support for all standard algorithms (HS256, RS256, ES256, etc.) means you can inspect tokens from any identity provider.