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JWT Decoder

Instantly decode JSON Web Tokens (JWT) to view payload and headers locally.

100% Client-Side Processing
Token Decoder
Encoded JWT
Header (Algorithm & Token Type)
Payload (Data)

What is JWT Decoder?

This JWT decoder parses a JSON Web Token and displays its header and payload as readable JSON, letting you inspect claims like expiration, issuer, and custom data without writing any code. It's built as a fast, privacy-respecting jwt.io alternative for developers debugging authentication and API issues. As a jwt decoder, it focuses purely on decoding and viewing — not verifying — the token's contents.

How It Works

The tool splits the JWT string on its periods into three segments, then base64url-decodes the header and payload segments and renders them as formatted JSON. It does not and cannot verify the token's signature, since valid signature verification requires the secret key or public key used to sign the token — a value your browser should never see or need for inspection purposes.

Is It Safe to Use?

All decoding happens locally in your browser's JavaScript; your JWT, which often contains sensitive session or identity data, is never transmitted to or logged by any server.

How to Use JWT Decoder (Step-by-Step Guide)

  1. Paste your JWT token into the input field.
  2. The tool automatically splits and decodes the header and payload.
  3. Review the decoded header (algorithm and token type) and payload (claims).
  4. Check expiration (exp), issued-at (iat), and custom claims as needed.
  5. Copy the decoded JSON for use in debugging or documentation.

Frequently Asked Questions

Does this tool verify my token's signature?
No, it only decodes and displays the header and payload as readable JSON — verifying a signature requires the secret or public key used to sign the token, which should never be entered into a browser-based tool.
Is this a safe jwt.io alternative?
Yes, it performs the same decode-only function as jwt.io's basic decoding feature, running entirely client-side so your token never leaves your browser.
Why can't a decoder check if my JWT is valid?
Validity checking requires cryptographically verifying the signature against the key that created it; without that secret or public key, a decoder can only show you what the token claims, not confirm it hasn't been tampered with.
Is it safe to decode jwt online tokens containing sensitive data?
As long as the tool processes everything locally in your browser without sending data to a server (as this one does), decoding is safe — but always be cautious pasting production tokens into any third-party tool.
What's inside a decoded JWT payload?
The payload typically contains claims like the subject (sub), expiration time (exp), issued-at time (iat), issuer (iss), and any custom application-specific data the token was signed with.
Why does a JWT have three parts separated by periods?
The three parts are the base64url-encoded header (algorithm info), payload (claims), and signature — the signature is what a server uses to verify the first two parts haven't been altered.
Can I use this jwt parser online to debug an expired token error?
Yes, decoding the payload lets you check the 'exp' claim directly to see exactly when the token expired, which is one of the most common sources of authentication bugs.
Does decoding a JWT require the signing secret?
No, the header and payload are only base64url-encoded, not encrypted, so they can be read by anyone without any key — only verifying the signature requires the secret or public key.
Report an issue with this tool