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JWT Decoder

Decode JWT header and payload

Empty-input detection · Limit 10MB per request Data is processed locally in your browser

Format: pending / invalid

JWT Token Input

All processing happens locally in your browser

Features

Format Detection & Parsing

Automatically recognizes standard JWT (header.payload.signature), decodes header and payload into readable JSON, and displays the signature.

exp / iat Analysis

Reads exp (expiration) and iat (issued at) claims, converts them to readable time, and calculates expiry status and remaining validity.

Security Checkup

Runs 6 security checks: expired, missing exp, alg=none (high risk), missing iat/iss, plus an overall health indicator.

Private · Local Parsing

Tokens are parsed entirely in your browser and never sent to any server, safe for real production tokens.

How to Use

Step 1: Paste your token

Paste a JWT token into the input area, or click "Load Demo Token" (locally constructed, not a real credential).

Step 2: View the result

Click "Decode Token" to view the header, payload, signature, time analysis and security check results.

Step 3: Identify risks

Focus on danger (red) and warning (yellow) items in the security checks, such as alg=none or expired tokens.

常见问题

Is the JWT decoder free?

Yes, completely free with no registration or usage limits.

Will my token be sent to a server?

No. All parsing happens locally in your browser. Tokens never leave your device, safe for real production credentials.

What does alg=none mean?

alg=none means the token has no signature, so attackers can forge tokens arbitrarily. Real services must reject alg=none; the tool flags it as high risk.

Can it verify the signature's authenticity?

No. Signature verification requires the server-side secret. This is a static parsing tool that displays the signature only.

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