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JWT Decoder

Decode and inspect JSON Web Tokens instantly.

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What is a JSON Web Token (JWT)?

A JSON Web Token (JWT) is an open industry standard (RFC 7519) method for securely transmitting information between two parties as a JSON object. Because JWTs are digitally signed, the information they contain can be verified and trusted. JWTs are overwhelmingly used in modern web applications for stateless authentication and API authorization. A standard token consists of three parts separated by dots (`.`): a Header (which dictates the signing algorithm), a Payload (which contains the user data or "claims"), and a Signature (used to verify the token hasn't been tampered with). However, because the Header and Payload are merely Base64Url encoded—and not encrypted—anyone can read the contents of a token. This JWT Decoder tool allows developers to quickly un-encode tokens to inspect the data inside them.

How to Use the JWT Decoder

Debugging your authentication flow is simple with this tool. Just follow these steps:

  • Acquire Your Token: Copy the raw JWT string from your browser's Local Storage, a cookie, or an HTTP Authorization header (typically starting with the word `Bearer `).
  • Paste the Token: Insert the raw string into the primary input box. Ensure you do not include the word "Bearer", just the token string itself.
  • Analyze the Output: The tool will instantly parse the token and display the decoded Header and Payload as properly formatted JSON objects.
  • Check Timestamps: Look for the `exp` (expiration time) and `iat` (issued at) claims. The tool often translates these Unix timestamps into human-readable dates so you can instantly see if your token has expired.

Crucial Security Reminders

  • JWTs are Not Encrypted: A common security vulnerability occurs when developers put sensitive information (like passwords, Social Security numbers, or API keys) inside the JWT payload. Anyone who captures the token can decode it using this exact tool. Only put non-sensitive identifiers (like user IDs or role names) in the payload.
  • 100% Client-Side Parsing: To protect your privacy and security, this decoder runs entirely in your web browser. Your token is never sent to our servers or saved in any logs.

Common Development Use Cases

A JWT decoder is an essential utility for backend engineers and frontend developers:

  • Debugging 401 Unauthorized Errors: If your API requests are suddenly failing, pasting your token here will quickly reveal if the `exp` claim has passed, meaning the token is expired.
  • Verifying User Roles: When implementing Role-Based Access Control (RBAC), developers decode the token to verify that the authentication server correctly injected the `roles` or `permissions` array into the payload.
  • Frontend State Management: Frontend applications often decode the token upon login to extract the user's name and avatar URL to display in the navigation bar without needing to make a separate API call.