Online JWT Decoder

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What is a JWT Decoder?

A JWT Decoder is a simple tool that takes a JSON Web Token (JWT) and breaks it into its three parts: the header, the payload, and the signature. JWTs are widely used in modern applications for authentication and authorization. They look like long strings of random letters and dots, but inside they carry structured information.

A JWT has three parts separated by dots:

header.payload.signature

The header describes the algorithm used for signing, the payload contains claims such as user ID or expiration date, and the signature secures the token.

The challenge is that JWTs are encoded in Base64URL format, which is not human-friendly. That is where a JWT Decoder comes in. It instantly translates the encoded token into readable JSON.

What Does Our JWT Decoder Do?

Our online tool accepts a JWT token as input and splits it into:

• Header: JSON object describing type and algorithm.
• Payload: JSON object with claims like user information and expiration.
• Signature: Base64URL string that can be verified by the server.

It does not validate the signature or check authenticity—it is a decoder, not a verifier. This means you can safely use it to inspect tokens without needing any secret keys.

Getting Started

1. Copy your JWT token.
2. Paste it into the tool’s input box.
3. Click Decode JWT.
4. Read the header, payload, and signature.
5. Copy useful fields like exp or user.
6. Use the knowledge to debug or improve your authentication system.

Input and Output Examples

Example 1: Simple JWT

Input

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyIjoiam9obmRvZSIsImV4cCI6MTcwMDAwMDAwMH0.sflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c

Output

Header

{
  "alg": "HS256",
  "typ": "JWT"
}

Payload

{
  "user": "johndoe",
  "exp": 1700000000
}

Signature

sflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c

Example 2: Role-based Token

Input

eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6MTAyLCJyb2xlIjoiYWRtaW4iLCJpYXQiOjE2OTg4ODg4ODh9.MEUCIQCn7aUo9tF7Lw1m3zDZGk4Iko0C4QfL_9UIMdX2h5jQIgWmDrBNHzQYa

Output

Header

{
  "alg": "ES256",
  "typ": "JWT"
}

Payload

{
  "id": 102,
  "role": "admin",
  "iat": 1698888888
}

Signature

MEUCIQCn7aUo9tF7Lw1m3zDZGk4Iko0C4QfL_9UIMdX2h5jQIgWmDrBNHzQYau

Frequently Asked Questions (FAQs)

What is JWT used for?

JWTs are used for securely transmitting claims between two parties, often in login and session management.

Can this tool verify JWT signatures?

No, it only decodes. Verification requires the secret or public key.

Are JWTs encrypted?

No, they are encoded but not encrypted. Anyone with the token can read the payload.

Does this tool keep my JWTs?

No, decoding happens in your browser only.

Can I decode tokens from any language?

Yes. JWTs are standardized, so decoding works across systems.

What is in the header?

Typically the algorithm (alg) and token type (typ).

What is in the payload?

Claims such as user data, expiration time, or roles.

What is the signature for?

It ensures the token has not been tampered with.

Can I modify the payload?

Yes, but the signature will not match, and servers will reject it.

Is this tool safe for production?

Yes, for decoding and learning. But never rely on it for verifying authenticity.

What if my JWT has only two parts?

It is invalid. A proper JWT always has three sections.

Benefits of Using Our JWT Decoder

• Quick insight into JWT structure.
• Helps debug authentication issues.
• No external servers—privacy preserved.
• Beginner-friendly interface.
• Works offline after loading.

Best Practices

• Never paste sensitive tokens from production if you are unsure of your environment.
• Remember: decoding ≠ verification. Always validate tokens in your backend.
• Use expiration (exp) claims properly to avoid stale tokens.
• Treat payload data as untrusted—it can be read and modified.

Thank You Note

I know if you made it this far, you probably really needed this tool. I hope it saved you time and maybe even a bit of frustration. I keep building new tools every week, some small and some surprisingly powerful. You can check out all our free tools here and make sure to bookmark CodeForGeek so you never lose us.

If you have an idea for improvement or something is not working right, just email me at [email protected]. I actually read those messages, and if your suggestion makes sense, I will add it.

Thanks for sticking around till the end. Now go try out your result before you forget why you came here.