JWT Decoder Online – Free JSON Web Token Inspector
Decode and inspect any JWT token in seconds. View the header, payload, and signature in a clean, readable format—entirely in your browser.
What Is a JWT Token?
A JSON Web Token (JWT) is an open standard (RFC 7519) for securely transmitting information between two parties as a JSON object. JWTs are widely used in modern web applications for authentication and authorization. When a user logs in, the server issues a JWT that the client stores and includes in subsequent requests to prove its identity.
A JWT consists of three parts separated by dots: the header, the payload, and the signature. The header specifies the signing algorithm (such as HS256 or RS256) and the token type. The payload contains the claims—statements about the user and additional metadata. The signature ensures that the token has not been altered after it was issued.
Each part is Base64URL-encoded, making the entire token URL-safe and compact. A typical JWT looks like a long string of characters: "eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiIxMjM0NTY3ODkwIn0.abc123". Decoding the first two parts reveals the JSON content, while the signature is binary data that verifies the token integrity.
How to Decode a JWT Token
- Open the decoder: Navigate to the JWT Decoder page on Base64 Shuttle. The tool loads instantly with no setup required.
- Paste your JWT: Copy the full JWT token string from your browser console, API response, or application storage and paste it into the input field.
- View the decoded parts: The tool automatically parses the token and displays the header JSON, payload JSON, and signature in separate sections.
- Inspect the claims:Review the payload for standard claims like "exp" (expiration), "iss" (issuer), "sub" (subject), and any custom claims your application uses.
Key Features
- Instant decoding: Paste a JWT and see the decoded header and payload immediately. No waiting or loading screens.
- Human-readable timestamps: Unix timestamps in claims like "exp", "iat", and "nbf" are converted to readable date and time format.
- Payload highlighting: Standard JWT claims are highlighted for quick identification, making it easy to spot expiration times and issuers.
- Complete privacy: All decoding happens in your browser. The JWT is never transmitted to any external server.
- Base64URL support: The decoder correctly handles Base64URL encoding, which differs slightly from standard Base64 encoding.
- Error detection: Invalid or malformed tokens are detected immediately with clear error messages explaining what went wrong.
- Works with any JWT: The tool supports JWTs signed with any algorithm (HS256, RS256, ES256, etc.), though it does not verify signatures.
Common Use Cases for JWT Decoding
Authentication debugging: When building or debugging authentication systems, you need to inspect the JWT tokens being issued. The decoder lets you verify that the payload contains the correct user information, roles, and permissions.
Token expiration checking:JWTs have a limited lifespan defined by the "exp" claim. When an application suddenly stops working, decoding the JWT can reveal whether the token has expired and needs to be refreshed.
API integration testing: When integrating with third-party APIs that use JWT authentication, you can decode the tokens to verify they contain the required claims and have not been tampered with.
Security auditing: Security professionals decode JWTs to audit the claims being transmitted, check for sensitive data leakage, and verify that tokens follow best practices for expiration and issuer validation.
Learning and education: JWT decoding is an excellent way to learn how JSON Web Tokens work. By examining real tokens, you can understand the structure, claims, and encoding used in modern authentication systems.
Understanding JWT Claims
JWT claims are key-value pairs in the payload that convey information about the token and the entity it represents. Registered claims are standardized and include "iss" (issuer), "sub" (subject), "aud" (audience), "exp" (expiration time), "nbf" (not before), and "iat" (issued at). Public claims are defined by the application and can carry any data. Private claims are agreed upon between parties and are not registered with any standard.
The decoder displays all claims in a formatted JSON view. Timestamps are automatically converted to human-readable dates, making it easy to check when a token was issued and when it will expire. This is invaluable when troubleshooting authentication issues in production environments.