What is a JSON Web Token (JWT)?
JSON Web Tokens (JWT) are an open, industry-standard method (RFC 7519) for securely transmitting information between two parties as a JSON object. This information can be verified and trusted because it is digitally signed. JWTs are overwhelmingly used in modern web development for authentication (e.g., keeping a user logged in without relying on session cookies) and secure information exchange.
A raw JWT looks like a long string of seemingly random characters, separated by two periods into three sections: Header.Payload.Signature. Because the Header and Payload are simply Base64Url encoded (not encrypted), anyone who possesses the token can easily decode it to read the contents.
Why You Need a Local JWT Decoder
When debugging API endpoints, authentication flows, or role-based access controls (RBAC), developers frequently need to inspect the contents of a JWT to check the claims. For example, you might need to check if the exp (expiration) timestamp has passed, or if the sub (subject) matches the expected user ID.
However, pasting active authentication tokens into generic online tools is a massive security risk. If a malicious site logs your active JWT, they can impersonate your user or gain unauthorized access to your systems. The WhiteArray JWT Decoder eliminates this risk. It is a zero-trust, completely client-side utility. The Base64 decoding happens entirely in your browser's memory. We do not have a backend that receives, stores, or logs your tokens.
Understanding JWT Claims
When you decode the payload of a JWT, you will see a JSON object containing "claims". Claims are statements about an entity (typically, the user) and additional data. There are three types of claims:
- Registered claims: These are a set of predefined claims which are not mandatory but highly recommended to provide a set of useful, interoperable claims. Common examples include
iss(issuer),exp(expiration time),sub(subject), andaud(audience). - Public claims: These can be defined at will by those using JWTs, but to avoid collisions they should be defined in the IANA JSON Web Token Registry or defined as a URI that contains a collision-resistant namespace.
- Private claims: These are custom claims created to share information between parties that agree on using them, such as a user's role (e.g.,
"role": "admin").
Frequently Asked Questions
Is it safe to decode my JWT online?
Yes, but only if the tool works entirely client-side. Our JWT Decoder parses your token directly in your browser. Your token is never transmitted to our backend servers, meaning your secure credentials cannot be intercepted or logged by us.
What information is inside a JWT?
A standard JSON Web Token consists of three parts: a Header (algorithm and token type), a Payload (the actual claims/data like user ID or expiration time), and a Signature (used to verify the token hasn't been tampered with).
Can this tool verify the signature of my JWT?
Currently, this tool is designed for inspecting the Base64Url encoded Header and Payload. Verifying the signature requires your private signing secret, which you should never paste into any online tool for security reasons.