Application Security
JWT Security Checker
Paste a JWT to decode the header and payload, check for algorithm none attack, expired tokens, and missing iss/aud claims without transmitting the token to any server.
No data is transmitted — everything runs locallyTool
About this tool
JWT Security Checker
The JWT Security Checker decodes JWT headers and payloads, checks for algorithm none and RS256-to-HS256 attacks, validates exp/iss/aud claims, and flags sensitive data in payload.
• Debug a JWT to inspect claims during API integration development
• Check for the algorithm none vulnerability in a JWT implementation
• Verify that exp, iss, and aud claims are present before shipping an auth flow
• Inspect a JWT from a log or error report to diagnose authentication failures
Affiliate disclosure
Credential and secrets management for teams. 1Password provides enterprise password management and secrets infrastructure for development teams.
View JWT secrets with 1Password
External site · Independent provider · We may receive a commission · Not a recommendation
FAQ
What does this tool tell you?
The JWT Security Checker decodes JWT headers and payloads, checks for algorithm none and RS256-to-HS256 attacks, validates exp/iss/aud claims, and flags sensitive data in payload.
What affects the result most?
Algorithm none attack: JWT with 'alg: none' header bypasses signature verification — must reject. RS256 to HS256 attack: server using public key as HMAC secret — verify algorithm is expected. exp claim validation: must reject expired tokens — common omission in JWT library integrations.
How should I use the result?
Treat the tool's output as a first-pass check, not a proof of correctness. A clean pass means no issues in the patterns this tool recognizes; a failure points to a specific problem you can investigate in your source. The underlying spec is the authoritative source for edge cases.
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