JWT Encoder/Decoder
Encode, decode, and verify JSON Web Tokens (JWT) with support for multiple algorithms
JWT Encoder / Decoder
Encode, decode, and verify JSON Web Tokens
JWT Token
About JSON Web Tokens
JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed.
Key concepts in JWT:
- Header: Contains the type of token and the signing algorithm being used.
- Payload: Contains the claims. Claims are statements about an entity (typically, the user) and additional data.
- Signature: Used to verify that the sender of the JWT is who it says it is and to ensure that the message wasn't changed along the way.
- Signing Algorithms: Different algorithms provide different security characteristics and require different types of keys.
Security Note: JWTs can be either signed, encrypted or both. If a token is signed, but not encrypted, everyone can read its contents, but when you don't know the private key, you cannot change it. Otherwise, the receiver will notice that the signature won't match anymore.
JWT Algorithm Comparison
Different JWT signing algorithms offer varying levels of security, performance, and key management requirements. Here's a comparison of the algorithms available in this tool:
| Algorithm | Type | Key Type | Security Level | Best For |
|---|---|---|---|---|
| HS256 | HMAC with SHA-256 | Symmetric | High | Simple applications where the same party issues and verifies tokens |
| HS384 | HMAC with SHA-384 | Symmetric | Very High | Applications requiring higher security than HS256 |
| HS512 | HMAC with SHA-512 | Symmetric | Very High | Applications requiring maximum security with HMAC |
| RS256 | RSA with SHA-256 | Asymmetric | High | Distributed systems where token issuer and verifier are different parties |
| RS384 | RSA with SHA-384 | Asymmetric | Very High | Applications requiring higher security than RS256 |
| RS512 | RSA with SHA-512 | Asymmetric | Very High | Applications requiring maximum security with RSA |
| ES256 | ECDSA with SHA-256 | Asymmetric | High | Mobile applications where token size and computational efficiency matter |
| ES384 | ECDSA with SHA-384 | Asymmetric | Very High | Applications requiring higher security than ES256 with ECDSA |
| ES512 | ECDSA with SHA-512 | Asymmetric | Very High | Applications requiring maximum security with ECDSA |
Example: Using JWT in Authentication
Here's a common flow for using JWTs in authentication:
- User logs in with credentials (username/password)
- Server verifies credentials and generates a JWT containing user identity and permissions
- Server sends the JWT to the client
- Client stores the JWT (typically in local storage or as a cookie)
- Client includes the JWT in the Authorization header for subsequent requests
- Server validates the JWT signature and grants access based on the claims in the payload
This stateless authentication mechanism is widely used in modern web applications, especially in microservices architectures.
JWT Implementation Examples
Here are examples of how to implement JWT encoding and decoding in different programming languages:
Best Practices for JWT Implementation
- Always use strong, randomly generated keys for signing
- Set appropriate expiration times for tokens
- Include standard claims (iat, exp, sub) when applicable
- Validate all claims on the server side
- Use HTTPS for token transmission
- Consider token refresh mechanisms for long-lived sessions
- Implement proper error handling for token validation
Common JWT Libraries
- JavaScript/Node.js: jsonwebtoken, jose
- Python: PyJWT, python-jose
- Java: jjwt, java-jwt
- PHP: firebase/php-jwt
- Go: golang-jwt/jwt
- Ruby: jwt gem
- C#: System.IdentityModel.Tokens.Jwt
DevToolCafe's free online JWT encoder and decoder is the ultimate tool for working with JSON Web Tokens. Debug, verify, and generate JWTs with support for all major algorithms including HS256, RS256, and ES256. Unlike other JWT tools, our decoder runs entirely in your browser — your tokens and secrets never leave your device. Perfect for debugging authentication issues, testing API integrations, and learning about JWT security. This is the best jwt.io alternative for developers who prioritize privacy.
What is a JSON Web Token (JWT)?
A JSON Web Token (JWT) is an open standard (RFC 7519) for securely transmitting information between parties as a JSON object. JWTs consist of three parts: a header (algorithm and token type), a payload (claims about the user), and a signature (verification). They're widely used for authentication, authorization, and information exchange in modern web applications, APIs, and microservices architectures.
Why Use Our JWT Tool?
Complete Privacy
All JWT encoding, decoding, and verification happens in your browser. Your tokens and secret keys never leave your device — essential for working with production tokens.
All Major Algorithms
Support for HMAC (HS256/384/512), RSA (RS256/384/512), and ECDSA (ES256/384/512) algorithms. Test any JWT regardless of signing method.
Signature Verification
Verify JWT signatures to ensure token integrity. Detect tampered tokens and validate that tokens were signed with the correct key.
Token Generation
Create new JWTs with custom headers and payloads. Perfect for testing authentication flows and API integrations.
How to Decode and Verify JWTs
Paste Your JWT
Copy your JWT token and paste it into the decoder. The tool instantly parses and displays the header and payload.
Inspect Claims
Review the decoded header (algorithm, type) and payload (sub, iat, exp, custom claims). Check expiration times and user data.
Verify Signature (Optional)
Enter your secret key or public key to verify the token's signature. The tool will confirm if the signature is valid.
Generate New Tokens
Switch to encode mode to create new JWTs. Enter your payload, select an algorithm, and sign with your key.