Free JWT Security Analyzer
Inspect JWT structure, claims, algorithms and common configuration risks before they become authentication weaknesses.
Paste Encoded Token
Decoded Header
Waiting for token...Decoded Payload (Claims)
Waiting for token...Signature Hash Code
JWT Authentication Flow
JWTs are stateless credentials. While they can be decoded client-side, the signature ensures cryptographic tamper-proofing. The backend must always verify this signature against a secure key.
The "alg: none" Exploit
Some legacy or misconfigured libraries process JWTs without verifying signatures when `"alg": "none"` is defined. Attackers exploit this to elevate privileges to administrative scopes.
JSON Web Key Sets (JWKS)
In modern B2B SaaS applications, public keys are dynamically exposed on a JWKS endpoint (e.g., `/.well-known/jwks.json`). This permits distributed API resource servers to verify token signatures asynchronously.
Need a Deeper Authentication Review?
Automated token decoding is only step one. Our lead practitioners manually audit token issuance flows, authorization parameters, multi-tenant boundaries, and session lifecycles.