JWT (JSON Web Token) is a compact, URL-safe means of representing claims to be transferred between two parties. It's commonly used for authentication and information exchange.

How does the JWT debugger work?

Our JWT debugger decodes the three parts of a JWT token: header, payload, and signature. It displays the decoded information in a readable format for analysis and debugging.

Is my JWT token safe when debugging?

Yes! All JWT decoding happens. in your browser. Your tokens never leave your device, ensuring complete privacy and security.

Can I verify JWT signatures?

Our tool decodes JWT tokens and displays signature information. For full signature verification, you would need the secret key, which we don't require for security reasons.

What JWT algorithms are supported?

Our debugger can decode JWTs using any algorithm (HS256, RS256, ES256, etc.). The algorithm is displayed in the header section of the decoded token.

JWT (JSON Web Token) is a compact, URL-safe means of representing claims to be transferred between two parties. It's commonly used for authentication and information exchange in web applications and APIs.

How does this JWT debugger work?

Our JWT debugger decodes JWT tokens by splitting them into three parts (header, payload, signature), decoding the Base64-encoded header and payload, and displaying the JSON data in a readable format. All processing happens. in your browser.

Is my JWT token data stored or transmitted?

No, all JWT decoding happens locally in your browser. We never transmit or store your JWT tokens on our servers. Your tokens remain completely private and secure.

Can I verify JWT signatures with this tool?

This tool decodes and displays JWT token contents. For signature verification, you need the secret key which should never be shared. We recommend using your application's backend for signature verification.

What information can I see in a decoded JWT?

You can see the header (algorithm and token type), payload (claims like user ID, expiration, issued at time), and the signature. Common claims include 'sub' (subject), 'exp' (expiration), 'iat' (issued at), and custom claims.

Is this JWT debugger free to use?

Yes, our JWT debugger is completely free with no registration required. All processing happens locally in your browser, ensuring your tokens are never transmitted or stored.

🎫 JWT Debugger

Decode and verify JSON Web Tokens (JWT). View header, payload, and signature instantly.

📝 Encoded JWT

🔍 What is JWT?

JSON Web Token (JWT) is a compact, URL-safe means of representing claims between two parties. It consists of three parts: Header, Payload, and Signature.

📊 JWT Structure

HeaderAlgorithm & token type

PayloadClaims & user data

SignatureVerification

💼 Common Uses

✅ User authentication
✅ API authorization
✅ Single sign-on (SSO)
✅ Information exchange

📋 Common JWT Claims

iss

Issuer

sub

Subject

aud

Audience

exp

Expiration

iat

Issued At

nbf

Not Before

jti

JWT ID

name

User Name

🎫 Understanding JSON Web Tokens (JWT)

JSON Web Tokens (JWT) have become the de facto standard for authentication and authorization in modern web applications and APIs. Developed as an open standard (RFC 7519), JWTs provide a compact, self-contained way to securely transmit information between parties as a JSON object. This information can be verified and trusted because it's digitally signed using either a secret (with HMAC algorithm) or a public/private key pair (using RSA or ECDSA).

The power of JWTs lies in their stateless nature. Unlike traditional session-based authentication where the server must store session data, JWTs contain all necessary information within the token itself. This makes them ideal for distributed systems, microservices architectures, and single-page applications where scalability and performance are critical.

A JWT consists of three parts separated by dots (.), each encoded in Base64Url format: the Header, the Payload, and the Signature. The header typically contains two parts: the type of token (JWT) and the signing algorithm being used (such as HMAC SHA256 or RSA). 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.

JWT debuggers are essential tools for developers working with authentication systems. They allow you to inspect the contents of a JWT token without needing to write custom code, making debugging authentication issues significantly easier. Whether you're troubleshooting why a token was rejected, verifying that claims are set correctly, or simply learning how JWTs work, a JWT debugger is an invaluable resource.

Our JWT debugger processes all tokens . in your browser. This means your authentication tokens never leave your device, ensuring complete privacy and security. This is particularly important since JWTs often contain sensitive user information and should be handled with care.

Understanding JWTs is crucial for modern web development. They're used by major platforms like Google, Microsoft, and Facebook for authentication, and are the foundation of OAuth 2.0 and OpenID Connect protocols. Whether you're building a REST API, implementing single sign-on (SSO), or creating a mobile application, JWTs are likely to be part of your authentication strategy.

📖 How to Use This JWT Debugger

Using our JWT debugger is straightforward and requires no technical setup:

Obtain Your JWT Token: JWT tokens are typically found in HTTP request headers (Authorization: Bearer <token>), cookies, or URL parameters. Copy the entire token including all three parts separated by dots.
Paste the Token: Paste your JWT token into the input field. The token should look like: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..
Automatic Decoding: The tool automatically decodes the token and displays the header and payload in a readable JSON format. You can see all claims, expiration times, and other metadata.
Inspect Claims: Review the decoded payload to understand what information the token contains. Common claims include user ID, email, roles, permissions, and expiration timestamps.
Check Expiration: Look for the "exp" (expiration) claim to see when the token expires. Expired tokens will be rejected by authentication systems.
Copy Decoded Data: Use the copy buttons to copy the decoded header or payload for use in documentation or debugging notes.

Important Note: This tool decodes and displays JWT contents but does not verify signatures. Signature verification requires the secret key or public key, which should never be shared. Always verify tokens on your backend server where keys can be securely stored.

💼 Real-World Use Cases

API Authentication

JWTs are widely used for authenticating API requests. When a user logs in, the server generates a JWT containing user information and permissions. Subsequent API requests include this JWT in the Authorization header, allowing the API to verify the user's identity without maintaining server-side sessions.

Single Sign-On (SSO)

Large organizations use JWTs to implement SSO across multiple applications. When a user logs into one application, they receive a JWT that can be used to access other applications in the same ecosystem without re-entering credentials. This improves user experience while maintaining security.

Mobile Application Authentication

Mobile apps often use JWTs because they don't require server-side session storage. The token is stored on the device and sent with each request. This stateless approach is ideal for mobile applications that need to work offline or with intermittent connectivity.

Microservices Communication

In microservices architectures, JWTs enable secure service-to-service communication. One service can issue a JWT that other services can verify without needing to query a central authentication server, reducing latency and improving scalability.

Information Exchange

JWTs can securely transmit information between parties. Because they're 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.

✅ JWT Security Best Practices

1. Keep Tokens Short-Lived

Set reasonable expiration times (typically 15 minutes to 1 hour) for access tokens. Use refresh tokens for longer sessions. Short-lived tokens minimize the risk if a token is compromised, as it will expire quickly.

2. Don't Store Sensitive Data

While JWTs are signed, they're not encrypted by default. Anyone who intercepts a JWT can decode it and read the payload. Never store passwords, credit card numbers, or other highly sensitive information in JWT payloads. Only include necessary user identification and authorization data.

3. Use Strong Signing Algorithms

Always use strong algorithms like RS256 (RSA with SHA-256) or ES256 (ECDSA with SHA-256) instead of HS256 (HMAC) when possible. RS256 allows you to verify tokens without sharing the private key, which is more secure for distributed systems.

4. Always Verify Signatures

Never trust a JWT without verifying its signature. An attacker could modify the payload and create a new token, but without the secret key, they can't create a valid signature. Always verify signatures on your backend before trusting any claims in the token.

5. Use HTTPS Only

Always transmit JWTs over HTTPS to prevent man-in-the-middle attacks. If a JWT is intercepted over an unencrypted connection, an attacker can read its contents and potentially use it for unauthorized access.

6. Implement Token Revocation

While JWTs are stateless, you should implement a token blacklist or revocation mechanism for security-critical applications. When a user logs out or their account is compromised, add the token to a blacklist that's checked on each request.

7. Validate All Claims

Don't just verify the signature—validate all claims. Check the expiration time (exp), not-before time (nbf), issuer (iss), and audience (aud) claims. This ensures the token is valid, intended for your application, and hasn't been tampered with.

🛡️ Privacy and Security Features

Our JWT debugger is designed with privacy and security as top priorities:

🔒.

All JWT decoding happens locally in your browser using JavaScript. Your tokens never leave your device, are never transmitted over the internet, and are never stored on our servers. This ensures complete privacy and eliminates the risk of server-side data breaches.

🚫 Privacy-focused

We don't use cookies, tracking scripts, or analytics that could compromise your privacy. Our tool is completely anonymous—we don't know who uses it, when they use it, or what tokens they decode. Your privacy is guaranteed.

✅ No Signature Verification (By Design)

Our tool intentionally does not verify JWT signatures. This is a security feature—signature verification requires secret keys that should never leave your secure backend. By only decoding tokens, we ensure that sensitive cryptographic keys are never exposed or transmitted.

🌍

Since we don't collect, process, or store any personal data, our tool is fully compliant with GDPR (General Data Protection Regulation) requirements. You can use our debugger for any purpose, including enterprise applications.

❓Frequently Asked Questions - JWT Debugger

Guide

How to use this tool well

JSON Web Tokens carry signed claims between services. Paste a token here to read the header and payload — decoding happens locally; treat production tokens as secrets.

Runs in your browserInputs are processed on your device. We do not receive generated secrets from this tool.Updated 2026-05-17

The three Base64URL parts

A JWT looks like header.payload.signature. The header usually states alg (e.g. HS256, RS256) and typ JWT. The payload holds claims such as sub (subject), exp (expiry), and custom roles.

The signature proves integrity: only someone with the secret or private key should create a valid token. This debugger decodes; it does not verify signatures unless you supply keys in your own workflow.

Mistakes we see in real projects

Accepting alg:none or switching asymmetric algorithms because the header said so — always pin allowed algorithms server-side.

Storing sensitive PII in the payload. JWTs are Base64, not encrypted; anyone with the string can read it.

Ignoring exp and nbf. Clock skew between servers can cause “random” logouts; allow a small leeway in validation code.

Common questions

Is it safe to paste my production JWT here?: Decoding is local, but anyone shoulder-surfing or with access to your screen can read claims. Use expired test tokens when possible; rotate if a live token was exposed.
Why does the signature show as invalid?: This tool focuses on inspection. Validating HS256/RS256 requires the correct secret or public key in your backend — not in a public web form.

Editorial standards: how we write and review guides.

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