JWT Decoder

What Is a JWT Decoder?

A JWT decoder is a developer tool that takes a JSON Web Token string and decodes its three parts: the header (algorithm and token type), the payload (claims like user ID, name, and expiration), and the signature. Our free online JWT decoder instantly decodes any JWT token, checks expiry status, annotates standard claims, and can verify HMAC-SHA256 signatures — all in your browser with complete privacy.

How to Use This JWT Decoder

Paste your JWT token into the input area. The tool instantly decodes and displays the header and payload as formatted JSON with syntax highlighting. The token is color-coded: blue for header, green for payload, red for signature. If the token has an exp claim, a badge shows whether the token is valid or expired. Hover over standard claim names (iss, sub, aud, exp, etc.) to see what each means. Use the signature verification panel to check HMAC-SHA256 signatures with your secret key.

Key Features

• Instant auto-decode — no button click needed, decodes as you paste
• Color-coded token display — header (blue), payload (green), signature (red)
• Expiry status badge — green/red/gray badge showing token validity
• Timestamp formatting — exp, iat, nbf converted to human-readable dates
• Claim annotations — hover tooltips explaining standard registered claims
• HMAC-SHA256 signature verification — verify with secret key via Web Crypto API
• Token builder — create unsigned test JWTs by editing header and payload
• Token comparison — side-by-side diff of two JWT payloads
• Validation warnings — alerts for expired tokens, alg:none, missing exp
• URL/header extraction — paste a full URL or Authorization header to extract the JWT
• Dark mode — toggle between light and dark decode panels

Why Choose Our JWT Decoder?

Unlike jwt.io, our JWT decoder runs 100% client-side — your sensitive authentication tokens never leave your browser. The tool automatically detects and warns about common security issues like unsigned tokens (alg: none), expired tokens, and missing expiration claims. The token builder lets you create test JWTs without external libraries. No signup, no ads, no tracking.

Common Use Cases

• Backend developers — debugging JWT authentication flows and inspecting token claims
• Frontend developers — decoding access tokens from OAuth providers to check user permissions
• QA engineers — verifying JWT contents in API test responses
• Security engineers — checking token expiry, algorithm, and signature validity
• DevOps engineers — troubleshooting service-to-service authentication with JWT bearer tokens

Tips and Best Practices

Always check the alg header claim — tokens with alg: none are unsigned and should never be trusted. Verify that the exp claim exists and is set to a reasonable time window. For production applications, always verify signatures server-side, not just decode payloads. Remember that JWT payloads are Base64-encoded, not encrypted — anyone can decode them, so never put sensitive data like passwords in JWT claims. Use short-lived tokens (15-60 minutes) with refresh tokens for better security.