Free Developer Tool
JWT Debugger
Decode and verify JSON Web Tokens instantly. Inspect headers, payloads, and verify signatures with your secret key. 100% client-side processing - your tokens never leave your browser.
Verify Signature
Quick Usage Guide
Decoding Tokens
Simply paste your JWT to instantly decode the header and payload. No server communication - everything happens in your browser.
Signature Verification
For HS256/HS384/HS512 tokens, enter your secret key to verify the signature. RSA/EC algorithms require public keys (not yet supported).
JWT 101
What is a JWT?
JSON Web Token (JWT) is a compact, URL-safe token format used for securely transmitting information between parties. It consists of three parts: header, payload, and signature, separated by dots.
JWT Structure
header.payload.signature
Each part is Base64URL encoded. The header contains the algorithm, payload contains claims,
and signature ensures integrity.
Common Claims
iss (issuer),
sub (subject),
aud (audience),
exp (expiration),
iat (issued at),
nbf (not before).
Security Considerations
JWTs are signed, not encrypted - anyone can read the payload! Never store sensitive data in JWTs. Always verify signatures server-side. Use short expiration times and HTTPS only.
Common Signing Algorithms
| Algorithm | Type | Description |
|---|---|---|
| HS256 | HMAC + SHA-256 | Symmetric key. Fast, simple. Shared secret between parties. |
| HS384 | HMAC + SHA-384 | Symmetric key. Stronger hash than HS256. |
| HS512 | HMAC + SHA-512 | Symmetric key. Strongest HMAC variant. |
| RS256 | RSA + SHA-256 | Asymmetric. Private key signs, public key verifies. |
| ES256 | ECDSA + P-256 | Asymmetric. Smaller keys, faster than RSA. |
| none | No signature | Insecure! Never accept in production. |
Common Use Cases
Authentication
After login, servers issue JWTs that clients include in subsequent requests. Stateless authentication without server-side sessions.
API Authorization
JWTs carry permissions and roles. APIs can verify tokens and authorize requests without database lookups.
Single Sign-On
Share authentication across multiple applications. One JWT works across your entire ecosystem of services.
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