Developer Tools

JWT Decoder

JWT Decoder

Decode and inspect JSON Web Tokens (JWT) in real-time.

JWT Token (encoded)

Token Claims Metadata

AlgorithmHS256

Token TypeJWT

Issuer (iss)None

Subject (sub)1234567890

Audience (aud)None

Expiration (exp)9/26/2049, 3:17:02 AM

Issued At (iat)1/18/2018, 1:30:22 AM

Part 1: Header

Token Metadata

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

Part 2: Payload

Decoded Claims

{
  "sub": "1234567890",
  "name": "Partha Sarathi",
  "admin": true,
  "iat": 1516239022,
  "exp": 2516239022
}

What is JWT Decoder?

A JSON Web Token (JWT) Decoder parses three-part tokens (Header, Payload, and Signature) encoded using base64url. This tool flattens the token segments and presents them as formatted JSON objects, allowing developers to inspect credentials, algorithm definitions, and custom claims instantly.

How to Use JWT Decoder

Paste your encoded JSON Web Token (a string containing two dot separators) into the token input box.
The tool immediately triggers decoding without requiring form submissions.
Inspect the **Header** (Part 1) for metadata and the **Payload** (Part 2) for claim variables.
Examine the claims metadata card highlighting Expiration (exp), Issued At (iat), and Issuer (iss) details.

Benefits of JWT Decoder

100% Offline: Decoding is performed completely inside browser scripting contexts; your tokens never hit any network endpoints.
Readable Claims: Converts timestamps to readable date and time formats automatically.
Segment Copying: Quick actions copy individual segments (Header or Payload) rather than the whole token structure.

Frequently Asked Questions (FAQ)

Does this tool verify the signature?

No. This tool operates on client-side decoding only and does not verify token authenticity against cryptographic public/private keys.

Is it safe to paste credentials here?

Yes. The decoding scripts run isolated in your browser tab. No external telemetry or trackers are configured to monitor payloads.

Detailed Technical Guide

Everything You Need to Know About JWT Decoder

Learn how to use our client-side JWT Decoder tool efficiently, understand the technical concepts, and explore FAQs.

What is JWT Decoder?

JWT Decoder is a web-based utility designed to inspect, parse, and verify JSON Web Tokens (JWT) directly in the browser. A JSON Web Token is a compact, URL-safe means of representing claims to be transferred between two parties. The claims in a JWT are encoded as a JSON object that is used as the payload of a JSON Web Signature (JWS) structure or as the plaintext of a JSON Web Encryption (JWE) structure, enabling the claims to be digitally signed or integrity protected with a Message Authentication Code (MAC) and/or encrypted. A standard JWT consists of three segments separated by dots (`.`): the Header, the Payload, and the Signature. The JWT Decoder parses the first two Base64URL-encoded segments and renders the underlying JSON structures in a readable format, displaying token metadata, expiration dates, scope arrays, and user identifiers.

Why use JWT Decoder?

When authentication failures occur, developers need to verify the token claims (e.g. check the expiration claim `exp` or issuer `iss`). Copy-pasting sensitive access tokens containing user details and system scopes into server-side online validators is highly insecure, as anyone capturing those tokens could gain unauthorized access to your APIs. ParthaTools JWT Decoder performs the decoding entirely on the client-side. The signature is analyzed and the claims are read locally, ensuring that access tokens are never leaked to third parties.

Privacy & Client-Side Sandbox Guarantee

Token parsing, claim extraction, and formatting are done entirely locally. No tokens are sent to any API endpoints, database servers, or log collectors. Your authentication details remain entirely private.

Key Features

Segment Isolation: Decodes and color-codes Header, Payload, and Signature components separately.
Date Parsing: Automatically converts Unix timestamps in claims (such as exp, iat, nbf) into readable local dates.
Algorithm Info: Displays signature details, key configurations, and header algorithms (e.g. HS256, RS256).
Client-Side Verification: Inspects tokens securely within browser runtime memory.

Common Use Cases

Debugging Login Issues: Verifying if OAuth/OIDC tokens have expired or contain the correct roles and permissions.
Inspecting API Headers: Checking token payloads extracted from developer consoles or network requests.
Testing Token Expiration: Verifying token parameters during local software development.

Frequently Asked Questions

The decoder extracts and displays the signature algorithm and headers. Full verification requires checking against your private keys, which should only be done in a secure server-side environment.

The colors match the three components of the token: Header (red/pink), Payload (purple/violet), and Signature (blue/cyan), making it easy to identify individual segments.

Base64URL is a variant of Base64 that uses URL-safe characters, replacing '+' with '-' and '/' with '_', and omitting padding characters ('=') to prevent encoding conflicts in query parameters.

You can modify the JSON payload for testing, but signing it requires access to the original private key or secret passphrase, which should never be exposed to the browser.

The decoder reads the 'exp' claim, converts it to a standard date format, and compares it to your system's current time, highlighting if the token is already expired.

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