JWT Decoder - Free Online JSON Web Token Decoder Tool
JSON Web Tokens (JWTs) are a compact, secure way to transmit information between parties as JSON objects. They are widely used for authentication and data exchange in modern web applications, APIs, and microservices. However, JWTs are encoded in a way that makes their contents unreadable without decoding. This is where a JWT Decoder comes in handy.
What is a JWT (JSON Web Token)?
A JWT (JSON Web Token) is a secure, compact, and URL-safe way of transferring data between two parties. It is typically used for authentication and authorization in RESTful APIs, Single Sign-On (SSO) systems, and microservices. A JWT consists of three main parts:
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Header: Contains metadata about the token, including the signing algorithm and token type.
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Payload: Contains the actual claims or data being transferred, such as user information, expiration time, and issuer.
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Signature: Used to verify the authenticity of the token and ensure it has not been tampered with.
JWT Structure
A typical JWT looks like this:
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c
This is divided into three parts, separated by dots:
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Header:
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9 -
Payload:
eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ -
Signature:
SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c
How JWT Decoding Works
Decoding a JWT involves extracting the Header, Payload, and Signature from the token. The header and payload are Base64URL encoded, while the signature is a cryptographic hash. Decoding a JWT reveals the raw JSON data, allowing you to inspect the claims and validate the token's contents.
Why Use a JWT Decoder?
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Inspect Token Contents: Quickly view the data stored in a JWT.
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Validate Tokens: Ensure the integrity of the token before trusting it.
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Debug API Authentication Issues: Identify issues with token generation and validation.
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Security Analysis: Check for potential vulnerabilities in token structure.
Features of the JWT Decoder Tool
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Instant Decoding: Quickly decode JWTs without any server processing.
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Header, Payload, and Signature Separation: View each part of the JWT separately.
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Copy to Clipboard: Easily copy the decoded content for use in your projects.
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Error Handling: Detect invalid JWT formats and base64 encoding errors.
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Responsive Design: Works seamlessly on desktop and mobile devices.
How to Use the JWT Decoder Tool
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Paste your JWT into the input field.
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Click "Decode JWT" to view the decoded Header, Payload, and Signature.
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Use the "Copy" buttons to quickly copy each section.
Example JWT for Testing
Sample JWT:
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c
Decoded Header:
{
"alg": "HS256",
"typ": "JWT"
}
Decoded Payload:
{
"sub": "1234567890",
"name": "John Doe",
"iat": 1516239022
}
Signature:
SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c
Common Use Cases for JWTs
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User Authentication: Securely verify the identity of users.
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API Authorization: Control access to protected API endpoints.
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Single Sign-On (SSO): Enable seamless login across multiple platforms.
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Data Integrity: Ensure data has not been tampered with.
Conclusion
JSON Web Tokens (JWTs) are a powerful tool for secure, stateless authentication and data transfer. Whether you're building APIs, microservices, or modern web applications, understanding how to decode and validate JWTs is essential for keeping your systems secure. Try our free JWT Decoder today to quickly inspect your tokens and improve your application's security.