JWT Encoder/Decoder

A JWT Encoder/Decoder is a specialized developer tool for creating, analyzing, and validating JSON Web Tokens (JWT). JWTs are compact, URL-safe tokens for authentication and authorization in modern web applications and APIs. They consist of three Base64-encoded parts: Header (algorithm), Payload (claims/data), and Signature (verification).

Our free online JWT tool offers both decoder and encoder functionality. In decode mode, you can analyze existing JWTs, understand their structure, and validate claims. In encode mode, you create new JWTs with configurable parameters like algorithm (HS256, RS256, etc.), expiration time, issuer, and audience – perfect for API testing, authentication debugging, and token development.

JSON Web Tokens are the de facto standard for authentication in REST APIs, microservices, and single-page applications (SPAs). OAuth 2.0, OpenID Connect, and almost all modern auth systems (Auth0, Firebase, AWS Cognito) use JWTs. Without solid understanding of JWT structure and validation, secure authentication implementation is practically impossible.

The biggest challenge in JWT development is debugging. When a token returns "Invalid Signature," there can be dozens of causes: wrong algorithm, expired token, wrong secret, incorrect claims. Our JWT decoder immediately shows where the problem is – you see header, payload, and signature separately and get detailed validation errors.

For backend developers, a JWT tool is essential when implementing authentication middleware, testing token generation and validation, and debugging CORS and authorization problems. Frontend developers need it to understand token contents, test API calls with bearer tokens, and debug session management problems.

Our tool offers a powerful decoder that breaks JWTs into their three components: Header (shows algorithm and token type), Payload (shows all claims like sub, iss, exp, aud), and Signature (shows the Base64-encoded signature). Automatic validation checks token structure, expiration, issuer, and other standard claims according to RFC 7519.

The encoder enables quick token generation with configurable parameters. Choose between different algorithms (HS256, HS384, HS512, RS256, RS384, RS512), set expiration time with practical syntax (1h, 7d, 3600s), and add standard claims like issuer, audience, and subject. The generated token can be immediately copied and used in API requests.

Practical additional features accelerate the workflow: Sample tokens for different scenarios (Simple, Complex, Expired) for quick testing. Automatic detection of expired tokens with warnings. Detailed error and warning messages for invalid token structures. Copy-to-clipboard function for all token parts (header, payload, signature, complete token).

API Authentication: Implement JWT-based authentication for REST APIs. Generate access tokens after user login, validate tokens in auth middleware, and implement refresh token flows.

Microservices Security: Use JWTs for service-to-service authentication. With JWTs, microservices can exchange claims about user permissions and roles without needing central session stores.

Single Sign-On (SSO): Implement SSO flows with JWTs. OpenID Connect uses JWTs for ID tokens that contain user information and authentication timestamps.

Stateless Sessions: Replace server-side sessions with JWTs. All session data is stored in the token itself (user_id, roles, permissions), which simplifies horizontal scaling.

API Testing and Debugging: Test protected API endpoints with different token configurations. Simulate expired tokens, missing claims, or wrong signatures to validate error handling.

Token Security Audits: Analyze existing JWT implementations for security vulnerabilities. Check if sensitive data is in the payload (JWTs are Base64-encoded, not encrypted!), if expiration times are set sensibly, and if the correct algorithm is used (never "none"!).