Free Online JWT Decoder - Debug JSON Web Tokens Instantly 2026

Welcome to Code Formatter JWT Decoder – the fastest, most secure online tool for decoding, inspecting, and debugging JSON Web Tokens (JWT). Our professional-grade decoder instantly reveals the contents of any JWT, showing you the header, payload claims, and signature structure with beautiful formatting. All processing happens 100% client-side in your browser, ensuring your sensitive authentication tokens never leave your computer.

JSON Web Tokens are the industry standard for secure authentication in modern web applications. Whether you're debugging OAuth flows, troubleshooting API authentication, or learning about token-based security, our JWT decoder provides the visibility you need to understand what's inside your tokens.

How to Use Our JWT Decoder Tool

Decoding JWTs has never been easier. Our intuitive interface shows results instantly as you type:

1. Paste Your JWT: Enter your JSON Web Token in the left "JWT Token" pane. The token should be in the standard format: header.payload.signature
2. Instant Decoding: The decoded header and payload appear immediately in the right pane, with color-coded sections for easy reading.
3. Inspect Claims: Review all payload claims including subject (sub), expiration (exp), issued at (iat), and any custom claims your application uses.
4. Check Expiration: Our tool automatically detects expiration timestamps and shows whether your token is still valid or has expired.

Understanding JWT Structure

A JSON Web Token consists of three parts separated by dots (.):

1. Header (JOSE Header)

The header typically contains two properties: the token type (typ), which is JWT, and the signing algorithm (alg) being used, such as HMAC SHA256 (HS256) or RSA (RS256). This information tells the receiving system how to verify the token's signature.

2. Payload (Claims)

The payload contains the claims – statements about the user and additional metadata. Standard claims include sub (subject), exp (expiration time), iat (issued at), iss (issuer), and aud (audience). Applications can also include custom claims like user roles, permissions, or profile information.

3. Signature

The signature is created by encoding the header and payload, then signing with a secret key (for HMAC algorithms) or private key (for RSA/ECDSA). This signature verifies that the token wasn't tampered with and, in the case of signing with a private key, authenticates the sender.

Common JWT Claims Explained

• sub (Subject): The principal that is the subject of the JWT, typically a user ID.
• iss (Issuer): The entity that issued the token, often your authentication server URL.
• aud (Audience): The recipients the JWT is intended for, usually your application identifier.
• exp (Expiration Time): Unix timestamp after which the token should not be accepted.
• iat (Issued At): Unix timestamp when the token was issued.
• nbf (Not Before): Unix timestamp before which the token should not be accepted.
• jti (JWT ID): Unique identifier for the token, useful for preventing replay attacks.

Security Best Practices for JWTs

When working with JSON Web Tokens, keep these security considerations in mind:

• Never Store Sensitive Data: JWTs are encoded, not encrypted. Anyone can decode and read the payload. Never include passwords, credit card numbers, or other sensitive information in JWT claims.
• Use Short Expiration Times: Set reasonable expiration times and implement token refresh mechanisms. A stolen token with a long expiration is a significant security risk.
• Validate All Claims: Always verify the signature, check expiration, and validate the issuer and audience claims on your server.
• Use Strong Secrets: For HMAC-signed tokens, use cryptographically random secrets of at least 256 bits. Never use predictable or short secrets.
• Prefer RS256 over HS256: For distributed systems, RSA signatures allow public key verification without exposing the private signing key.

Why Choose Code Formatter JWT Decoder?

Our JWT decoder stands out for its commitment to privacy, security, and usability:

• 100% Client-Side: Your tokens never leave your browser. Zero server uploads, zero logging, complete privacy.
• Instant Decoding: See results in real-time as you paste or type your token.
• Beautiful Formatting: Color-coded sections and organized claims make reading complex tokens effortless.
• Expiration Detection: Automatic detection of token expiration status saves debugging time.
• Works Offline: After initial load, the decoder works without internet connection.

Frequently Asked Questions

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