JWT Decoder

🔐 JWT Decoder – Decode and Inspect JSON Web Tokens

The JWT Decoder is a client-side tool that allows you to decode and inspect JSON Web Tokens (JWTs). Whether you're a developer, security professional, or just curious about what's inside a JWT, this tool makes it easy to view the contents without sending your tokens to a server.

This guide explains what JWTs are, how they work, and walks you through using our free online decoder to inspect token contents.

📘 What are JSON Web Tokens (JWTs)?

JSON Web Tokens (JWTs) are an open standard (RFC 7519) that define a compact and self-contained way for securely transmitting information between parties as a JSON object. JWTs are commonly used for:

• Authentication: Once a user logs in, each subsequent request will include the JWT, allowing the user to access routes, services, and resources permitted with that token.
• Information Exchange: JWTs are a good way of securely transmitting information between parties because they can be signed, ensuring the sender is who they claim to be.

🧩 Structure of a JWT

A JWT consists of three parts separated by dots (.):

                header.payload.signature
                

1. Header: Contains metadata about the token, such as the type of token and the signing algorithm used.
2. Payload: Contains the claims or the data being transmitted.
3. Signature: Used to verify that the sender of the JWT is who it says it is and to ensure the message wasn't changed along the way.

Both the header and payload are Base64URL encoded JSON objects. The signature is created using the encoded header, encoded payload, a secret, and the algorithm specified in the header.

🔍 Common JWT Claims

The payload of a JWT contains claims, which are statements about an entity (typically, the user) and additional data. There are three types of claims:

• Registered Claims: Predefined claims that are not mandatory but recommended to provide a set of useful, interoperable claims. Examples include:
  • iss (Issuer): Who issued the token
  • sub (Subject): Who the token is about
  • exp (Expiration Time): When the token expires
  • iat (Issued At): When the token was issued
  • nbf (Not Before): When the token starts being valid
  • jti (JWT ID): Unique identifier for the token
• Public Claims: Claims defined at will by those using JWTs. To avoid collisions, they should be defined in the IANA JSON Web Token Registry or be defined as a URI that contains a collision-resistant namespace.
• Private Claims: Custom claims created to share information between parties that agree on using them.

⚙️ How the JWT Decoder Works

Our JWT Decoder provides a simple interface to:

1. Paste your JWT into the input field
2. View the decoded header with token type and algorithm
3. Examine the payload with all claims in a readable format
4. See the signature part of the token

🧩 Key Features

• ⚡ Instant decoding as you type or paste
• 🔍 Pretty-printed, syntax-highlighted JSON
• 📊 Collapsible sections for header, payload, and signature
• 🔐 Client-side only — your tokens never leave your browser
• 📱 Mobile and desktop-friendly interface
• 🕒 Human-readable timestamps for expiration and issuance dates

🔐 Security Considerations

While JWTs are a secure way to transmit information, there are some important security considerations to keep in mind:

• Never share sensitive information in a JWT payload unless it's encrypted.
• Keep your signing keys secure and rotate them regularly.
• Set appropriate expiration times for your tokens.
• Validate all tokens on the server side before trusting their contents.
• Use HTTPS to prevent token interception during transmission.

Remember that this decoder only displays the contents of JWTs; it does not verify signatures or validate tokens. For security reasons, token verification should always be done on the server side with the appropriate secret or public key.

🔄 How to Use the JWT Decoder

1. Paste your JWT into the input field
2. The tool will automatically decode and display the token's contents
3. Expand or collapse the header, payload, and signature sections as needed
4. Examine the claims in the payload, with special attention to expiration times