JWT Decoder
Decode and inspect JSON Web Tokens instantly and securely.
Encoded JWT String
Decoded Data
HEADER (Algorithm & Token Type)
{}
PAYLOAD (Data & Claims)
{}
SIGNATURE (Verification)
Signature will appear here...
Free Online JSON Web Token (JWT) Decoder
Analyze, decode, and debug your API authentication tokens easily with our fast, secure, and developer-friendly JWT decoder.
JSON Web Tokens (JWT) are an open standard (RFC 7519) used widely in modern web development to securely transmit information between a client and a server as a JSON object. Whether you are building REST APIs, managing user authentication, or developing single-page applications (SPAs), dealing with JWTs is a daily task. The Online JWT Decoder by DoItToolz helps developers instantly unpack these tokens to verify the payload data, expiration times, and algorithms.
Structure of a JSON Web Token
A standard JWT string consists of three parts separated by dots (.). Our tool decodes each part automatically:
- Header: Contains the type of the token (JWT) and the signing algorithm being used, such as HMAC SHA256 (HS256) or RSA.
- Payload (Claims): Contains the actual data (claims). This usually includes user IDs, roles, email addresses, and token expiration timestamps (
exp). - Signature: A hash created from the encoded header, encoded payload, and a secret key. It ensures the token hasn't been altered in transit.
Frequently Asked Questions (FAQs)
What is a JWT used for?
JWTs are primarily used for Authorization and Information Exchange. Once a user logs in, every subsequent API request will include the JWT, allowing the user to access routes, services, and resources permitted with that token.
Can a JWT be decoded without a secret key?
Yes! The Header and Payload of a standard JWT are simply Base64Url encoded, not encrypted. Anyone who intercepts the token can decode and read the data. This is why you should never put sensitive information like passwords in a JWT payload.
How does the Signature work?
While anyone can decode the payload, they cannot modify it without invalidating the token. The Signature is generated using a secret key known only to the server. If someone alters the payload, the signature won't match, and the server will reject the token.
Why Use Our JWT Debugger?
Debugging authentication errors (like a 401 Unauthorized response) can be frustrating. Often, the issue lies in an expired token or a missing claim. By pasting your token into our decoder, you can instantly read the exp (expiration) and iat (issued at) claims, verify user roles, and ensure the backend is generating the token correctly. Our tool formats the JSON output clearly with syntax highlighting to save you time during development.
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