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JWT Decoder

Decode and analyze JSON Web Tokens locally in your browser. Inspect headers, payloads, signatures, and claim definitions instantly.

Encoded Token

Paste Token Below

Signature Verification

HS256
Checking signature...
Signature validation is calculated client-side in your browser.

Decoded Contents

Header (Algorithm & Token Type)
Payload (Claims / Data)

Claims Dictionary

Interpretation of standard claims detected in your JWT payload.

Claim Raw Value Meaning & Status

Understanding JSON Web Tokens and Decoding Architectures

JSON Web Tokens (JWT) are a standardized format used for securely transmitting claims between parties. They are widely implemented in authorization headers, stateless API requests, single sign-on (SSO), and identity provider architectures like OAuth2.0 and OpenID Connect.

The Structure of a JSON Web Token

A standard JWT contains three distinct sections separated by dot character delimiters:

  • Header: Defines the envelope metadata, typically listing the signature algorithm (e.g. HS256, RS256) and the token media type (JWT).
  • Payload: Holds the core claims or attributes (such as user identifiers, issue timestamps, expiration times, and permissions profiles).
  • Signature: Created by encrypting or signing the encoded header and payload using a cryptographic key, preventing tampering of token data.

Evaluating JWT Claims and Timestamps

Deciphering claims requires translating UNIX timestamps into readable dates. This utility automatically detects standard claims:

  • exp (Expiration Time): Shows the timestamp after which the token is invalid. This tool compares it against the local system clock and displays a live expiry timer badge.
  • iat (Issued At): Displays the precise moment the auth token was created.
  • iss (Issuer): Identifies the authentication server or authority that signed the credentials.
  • sub (Subject): Represents the unique identifier or database primary key of the authenticated user.

Security Best Practices and Local Processing Privacy

Many online JWT decoders process data on external servers, introducing severe security risks if active production tokens are exposed. This utility resolves this risk by running entirely within the browser.

  1. All Base64URL string splitting and decoding are processed client-side. No API or server transmission is ever triggered.
  2. Signature validation utilizes the browser standard WebCrypto API, verifying HMAC-SHA256 tokens locally using your machine's hardware.
  3. You can safely verify production tokens, test claims, and check credentials without exposing keys or credentials.

Frequently Asked Questions

Is it safe to paste my JWT token into this online decoder?

Yes, it is completely secure. This JWT Decoder runs 100% client-side inside your browser. No token contents, payload data, or secret keys are transmitted to any server. Your sensitive auth tokens remain fully private to your local computer.

What are the three parts of a JWT?

A JSON Web Token (JWT) consists of three parts separated by dots: the Header (describes the token type and algorithm), the Payload (contains the claims or user data), and the Signature (used to verify that the token has not been altered).

How do I decode a JWT token using this tool?

Simply paste your encoded JWT token string into the input text area. The parser will instantly extract and decode the Base64URL-encoded header and payload, displaying them as formatted, editable JSON objects.

Does this tool verify the signature of the JWT?

Yes. The tool validates the signature structure. If you enter the corresponding secret key (for HS256 HMAC algorithms) or the public key, the decoder will compute and compare the signature locally using browser WebCrypto APIs to verify its authenticity.

What do standard claims like exp, sub, and iss mean?

These are standard registered claims: "iss" (issuer) identifies who created the token, "sub" (subject) identifies the user, and "exp" (expiration time) defines when the token becomes invalid. This tool automatically translates these Unix timestamps into readable local dates and displays their active status.

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