JWT decoder and signature checker

  1. Input
  2. Options
  3. Result

Input and settings

Verification mode

Choose the verification algorithm and use a trusted key. Reading fields without verifying the signature does not authenticate a token. Time checks use this device’s clock when you run the check. Limits: 65536 token characters and 16384 UTF-8 bytes for the key.

Processing runs on your device; the tool does not send the token or key to a server or fetch keys from URLs. A matching signature does not check the issuer (iss), intended recipients (aud) or access permissions in your application.

JWT decoder and signature checker

Read a JWT header and data fields in your browser. Optionally check an HS256 or RS256 signature with a key you supply, and inspect the exp, nbf and iat timestamps.

Quick start

JWT decoder and signature checker

  1. Paste a JWT. Use test data and test keys.
  2. Choose to read the fields only or verify the signature with a selected algorithm and trusted key.
  3. Check the signature result and timestamp fields separately.
✓ The tool runs directly in the browser and is ready for quick checks without installing software.
✓ Input can be cleared and recalculated immediately, which is useful for repeated small tasks.
✓ Use fullscreen mode when you need more space for long text, structured data or large result blocks.
✓ Copy buttons are available on generated output so results can be reused in code, documents or support chats.
✓ Most operations are deterministic: the same input and options produce the same output.
✓ For sensitive content, prefer local browser tools and review the result before sharing it further.

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