Development Tools
JWT Decoder — View Header, Payload & Signature
Decode JWT tokens free to readable JSON header and payload. Valid Format badge only — no signature verification. Paste a token and decode now.
TL;DR: Paste a JWT or load the sample, click Decode JWT, and see header and payload as pretty-printed JSON plus the raw signature — a Valid Format or Invalid Format badge reflects structure only. Signature verification is not performed.
Reviewed by FYN Tools Editorial · Guides ·
Privacy & processing: Decoding uses atob on base64url segments and JSON.parse in your browser. The token is never sent to a server. Valid Format means parseable structure, not cryptographic authenticity.
JWT Token Decoder
Decode JWT tokens free to readable JSON header and payload. Valid Format badge only — no signature verification. Paste a token and decode now.
- Inputs
- JWT string (header.payload.signature) or sample token via Load Sample
- Outputs
- Pretty JSON header, pretty JSON payload, raw signature, Valid/Invalid Format badge
- Processing
- Client-side (browser atob + JSON.parse)
- Limits
- Decode only — no signature verification; malformed tokens show Invalid Format
Quick steps
- Paste your JWT into the token textarea or click Load Sample.
- Click Decode JWT.
- Read the Valid Format or Invalid Format badge.
- Inspect the Header card for alg and typ fields.
- Inspect the Payload card for claims like sub, iat, and exp.
- Copy header, payload, or signature individually as needed.
- Decode JWT button
- Load Sample token
- Valid Format / Invalid Format badge
- Header, payload, signature cards
- Per-section copy buttons
Data input / output
| Inputs | JWT string (header.payload.signature) or sample token via Load Sample |
|---|---|
| Outputs | Pretty JSON header, pretty JSON payload, raw signature, Valid/Invalid Format badge |
| Formats | Base64url-encoded three-part JWT |
| Limits | Decode only — no signature verification; malformed tokens show Invalid Format |
| Processing | Client-side (browser atob + JSON.parse) |
How to Use the JWT Token Decoder
- Paste your JWT into the token textarea or click Load Sample.
- Click Decode JWT.
- Read the Valid Format or Invalid Format badge.
- Inspect the Header card for alg and typ fields.
- Inspect the Payload card for claims like sub, iat, and exp.
- Copy header, payload, or signature individually as needed.
What is a JWT Token Decoder?
Paste a three-part JWT and click Decode JWT. The header and payload segments are base64url-decoded (replacing - with + and _ with /) then parsed as JSON with two-space indentation. The signature segment displays as raw text.
A Valid Format badge appears when decoding succeeds; Invalid Format when the token lacks three parts or JSON parsing fails. Load Sample fills a well-known HS256 example token. The UI notes that signature verification requires the issuer secret, which this tool never requests.
decodeJWT splits on dots, requires exactly three parts, decodes the first two with atob, and sets isValid true on success. Each section has its own copy button; Clear resets all fields.
How it works
JWT Token Decoder reads your input from the panel above, applies decode jwt button, and shows a result you can copy or download. Options stay visible so you can iterate without reloading the page.
To encode or decode Base64 strings separately, use our Base64 Converter.
Common Use Cases & Examples
- API auth debugging: Decode an access token to verify the roles claim your backend should enforce.
- Expiry investigation: Read exp in the payload when clients report unexpected logouts.
- JWT learning: Load Sample to see a concrete HS256 header and payload before writing your own parser.
Input / Output Examples
Input
eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiIxMjM0NTY3ODkwIn0.dozjgNryP4J3jVmNHl0w5N_XgL0n3I9PlFUP0THsR8U
Output
Header: { "alg": "HS256" }
Payload: { "sub": "1234567890" }Frequently Asked Questions
What is a JWT token?+
JWT (JSON Web Token) is a secure way to transmit information between parties as a JSON object. It's commonly used for authentication and information exchange.
Is it safe to decode JWT tokens here?+
Yes, all JWT decoding happens locally in your browser. Your tokens are never sent to our servers, ensuring complete privacy and security.
Can I verify JWT signatures?+
Our tool decodes and displays JWT information but doesn't verify signatures, as that requires the secret key which should never be shared publicly.
What information can I see in a JWT?+
You can see the header (algorithm and token type), payload (claims and data), and signature. Common claims include expiration time, issuer, and user information.
Key Features
- Decode JWT button
- Load Sample token
- Valid Format / Invalid Format badge
- Header, payload, signature cards
- Per-section copy buttons
Benefits
See JWT claims without writing a decode script.
Speed up auth integration debugging.
Learn token structure hands-on from the sample.
When to Use JWT Token Decoder
- Debugging auth flows to see claims inside a returned token
- Checking exp or iat epoch values during session troubleshooting
- Learning JWT structure from the sample token
- Confirming which algorithm the header declares
Advantages
- Instant client-side decode
- Valid Format / Invalid Format badge
- Load Sample for immediate demo
- Separate copy buttons per section
Tips
- Valid Format does not mean the token is trustworthy — anyone can craft JWT-shaped strings.
- Avoid pasting production session tokens into shared machines.
- Check alg in the header before assuming HMAC versus RSA.
- Pair decode-only inspection with server-side verification in your app.
Common Mistakes
Treating Valid Format as proof of authenticity — signatures are never verified here.
Expecting the signing secret to appear in the decoded output.
Pasting tokens missing a segment and expecting partial JSON.
Sharing decoded payloads containing live user data without redaction.
Summary
Paste a JWT to decode header and payload JSON with a Valid Format badge — decode only, no signature verification.