vulnbeacon_TOOLS
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Identity & secrets

JWT debugger

Inspect a token entirely in your browser. Decoding does not establish authenticity or prove a vulnerability in the application that accepts it.

How to use JWT debuggerSteps, privacy & next steps

Decode a token locally and inspect its declarations without treating them as trusted identity.

Run this check

  1. Paste a compact three-part JWT or load the synthetic example.
  2. Optionally provide the trusted HS256 key for local signature verification.
  3. Analyze, review timing and claim warnings, and open the decoded view only when needed.

What you need

  • A compact JWT. The optional signing-secret field supports HS256 only.

Your input & privacy

The token and optional key remain in browser memory. Identity/custom claim values and signing secrets are excluded from copied plans and reports.

Read the result

Use the warnings to inspect your issuer and verifier configuration. Test application rejection with authorized synthetic tokens.

Keep in mind

  • Decoding does not authenticate a token. A signature match still does not validate issuer, audience, authorization or revocation.
  • No key discovery, server acceptance test or other signature algorithm verification is performed.

Your inputs, explained.

JWTs, source snippets, passwords, CSP text, files, hashes and Base64 are processed in browser memory. This toolkit does not upload or save those inputs.

Website checks send the approved URL to this service and contact the target. DNS checks disclose the domain to Cloudflare DNS over HTTPS. Email-breach checks send the full address to Have I Been Pwned when configured and explicitly requested.

Server checks are transient and rate limited. This application does not write tool input or result logs; your hosting provider and contacted services may retain network metadata under their own policies. Exports are saved only when you choose to download them.

Use tools only for assets you own or have permission to assess. Private scans and their saved reports use the separate authenticated VulnBeacon application.