Does decoding a JWT verify it?

No. Decoding only reads the Base64URL-encoded header and payload. Verifying requires checking the signature with the issuer's secret or public key on your server.

Is the data inside a JWT secret?

No. A standard signed JWT is encoded, not encrypted, so anyone with the token can read its payload. Never put secrets in JWT claims.

How do I use the JWT Decoder?

1. Paste the text or data you want to encode or decode into the input box. 2. Pick any options you need and run the JWT Decoder. 3. The result appears instantly — everything is processed in your browser. 4. Copy the result to your clipboard with one click.

Is the JWT Decoder free?

Yes. The JWT Decoder is 100% free, with no sign-up, no usage limits and no watermarks.

Is my text private when I use the JWT Decoder?

Yes. The tool processes your text locally in your browser using JavaScript. Your text is never uploaded to a server, stored or shared.

Does the JWT Decoder work on mobile?

Yes. It works in any modern browser on Windows, macOS, Linux, Android and iOS, including phones and tablets. There is nothing to download or install.

JWT Decoder - Decode JSON Web Tokens

Decode and inspect JWT tokens to view header and payload information in readable format.

JWT Token

Paste your JWT token here

Header

JWT header information

Payload

JWT payload (claims)

Complete Guide to JWT (JSON Web Tokens) and Token Decoding

JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object. JWTs are commonly used for authentication and authorization in modern web applications, APIs, and microservices. Understanding JWT structure and being able to decode tokens is essential for developers working with authentication systems, API security, and debugging authentication issues.

Understanding JWT Structure

A JWT consists of three parts separated by dots (.), which are: Header, Payload, and Signature. The header typically contains the token type (JWT) and the signing algorithm (e.g., HS256, RS256). The payload contains the claims, which are statements about an entity (typically the user) and additional metadata. The signature is used to verify that the sender of the JWT is who it says it is and to ensure that the message wasn't changed along the way. Our decoder focuses on the header and payload, which are Base64Url encoded JSON objects that can be decoded without the secret key.

JWT Components Explained

Header

The header typically contains two parts: the type of token (JWT) and the signing algorithm being used (e.g., HMAC SHA256 or RSA). Common algorithms include HS256 (HMAC with SHA-256), RS256 (RSA with SHA-256), and ES256 (ECDSA with P-256 and SHA-256). The header is Base64Url encoded and forms the first part of the JWT.

Payload

The payload contains the claims, which are statements about an entity and additional data. There are three types of claims: registered claims (like iss, exp, sub), public claims, and private claims. The payload is Base64Url encoded and forms the second part of the JWT. This is where user information, permissions, and expiration times are typically stored.

Signature

The signature is created by taking the encoded header, encoded payload, a secret, the algorithm specified in the header, and signing that. The signature ensures that the token hasn't been tampered with. To verify the signature, you need the secret key, which our decoder doesn't require since we only decode the header and payload.

Base64Url Encoding

JWT uses Base64Url encoding, which is similar to Base64 but uses URL-safe characters. The '+' and '/' characters are replaced with '-' and '_', and padding '=' characters are removed. This encoding makes JWTs safe to use in URLs and HTTP headers without encoding issues.

Common JWT Use Cases

Authentication

JWTs are widely used for user authentication. After a user logs in, the server generates a JWT containing user information and sends it to the client. The client includes this token in subsequent requests, and the server validates it to authenticate the user. This stateless approach is popular in RESTful APIs and microservices architectures.

Authorization

JWTs can contain authorization information like user roles and permissions. The server can check these claims to determine what resources a user can access. This eliminates the need to query a database for permissions on every request, improving performance in distributed systems.

Information Exchange

JWTs provide a secure way to transmit information between parties. Since they can be signed, you can be sure the senders are who they say they are. Additionally, if the JWT is encrypted, you can verify that the content hasn't been tampered with, making JWTs suitable for secure information exchange.

Single Sign-On (SSO)

JWTs are commonly used in SSO implementations. When a user authenticates with an identity provider, they receive a JWT that can be used to access multiple applications without re-authenticating. This improves user experience and simplifies authentication management across different services.

JWT Claims Explained

Registered Claims (Standard):

iss (issuer): Identifies who issued the JWT
sub (subject): Identifies the subject of the JWT (typically the user ID)
aud (audience): Identifies the recipients that the JWT is intended for
exp (expiration time): Identifies the expiration time after which the JWT must not be accepted
nbf (not before): Identifies the time before which the JWT must not be accepted
iat (issued at): Identifies the time at which the JWT was issued
jti (JWT ID): Unique identifier for the JWT

Security Considerations

⚠️ Important Security Notes

JWTs are encoded, not encrypted. Anyone can decode the header and payload without the secret key.
Never store sensitive information (like passwords) in JWT payloads.
Always validate JWT signatures on the server side before trusting the token.
Check expiration times (exp claim) to ensure tokens haven't expired.
Use HTTPS to prevent token interception during transmission.
Consider token refresh mechanisms for long-lived sessions.

Debugging with JWT Decoder

Our JWT decoder is invaluable for debugging authentication issues. Developers can decode tokens to inspect claims, verify expiration times, check user information, and understand token structure. This is particularly useful when troubleshooting authentication flows, verifying token contents, or understanding how different applications structure their JWTs. The decoder provides a human-readable view of the token's header and payload, making it easier to identify issues and understand authentication behavior.

Technical Implementation

Our JWT decoder processes tokens client-side in your browser, ensuring your tokens never leave your device. This provides maximum privacy and security, especially important when working with production tokens or sensitive authentication data. The decoder handles Base64Url decoding, JSON parsing, and formatting to provide a clear view of the token's structure and contents.

Instant Decoding

Decode JWT tokens instantly to view header and payload.

100% Private

All processing happens locally. Your tokens never leave your device.

Developer Friendly

Perfect for debugging authentication and understanding token structure.

JWT Decoder - Decode JSON Web Tokens

JWT Token

Header

Payload

Complete Guide to JWT (JSON Web Tokens) and Token Decoding

Understanding JWT Structure

JWT Components Explained

Header

Payload

Signature

Base64Url Encoding

Common JWT Use Cases

Authentication

Authorization

Information Exchange

Single Sign-On (SSO)

JWT Claims Explained

Security Considerations

⚠️ Important Security Notes

Debugging with JWT Decoder

Technical Implementation

Instant Decoding

100% Private

Developer Friendly

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