JWT Debugger & Signature Verifier
Decode JWT headers and payload claims, verify token signatures for HS/RS/ES algorithms, and troubleshoot authentication token issues with browser-only processing.
Decode JWT headers and payloads, inspect claims, and verify signatures for HS, RS, and ES algorithms using a shared secret or public key PEM directly in your browser.
Fast JWT Decoding
Decode JWT header and payload segments instantly with Base64URL handling and JSON parsing to inspect claims, algorithm metadata, issuer values, and token timeline fields.
Signature Verification Support
Verify HS, RS, and ES JWT signatures in-browser using a shared secret or public key PEM. Useful for debugging auth pipelines and validating token integrity in development and staging.
Claim Timeline Diagnostics
Detect common claim timing problems across exp, nbf, and iat fields to troubleshoot token expiry, activation windows, and clock-skew issues before they break production authentication flows.
Free and Private
JWT analysis and signature checks run locally in your browser with no server transfer. The tool is free to use without signup, making it practical for day-to-day auth debugging.
OAuth Debugging
Inspect bearer tokens issued by identity providers to confirm claims, issuer metadata, and signature validity during OAuth/OIDC integration testing.
API Gateway Validation
Verify JWT signatures before configuring API gateway policies to ensure key distribution and algorithm assumptions are correct across environments.
Incident Response
Analyze problematic access tokens from logs to determine whether failures are caused by malformed structure, invalid signatures, or expired claims.
Auth Migration Checks
Compare tokens before and after auth provider migration to validate algorithm compatibility and verify expected claim parity.
CI Security Reviews
Use deterministic verification reports in test pipelines to catch broken token issuance logic and key rotation mistakes early.
Developer Education
Help teams understand JWT internals by visualizing headers, claims, and signature outcomes in one place with clear diagnostics.
JWT Debugger & Signature Verifier is designed for practical authentication troubleshooting. It parses compact JWT tokens, decodes header and payload JSON, and verifies signatures using browser-native Web Crypto APIs for common HS, RS, and ES algorithms.
Supported Signature Modes
HMAC algorithms (HS256, HS384, HS512) are verified with a shared secret. RSA algorithms (RS256, RS384, RS512) and ECDSA algorithms (ES256, ES384, ES512) are verified using public key PEM input. The verifier maps algorithm metadata to corresponding hash and key import settings.
Claim Diagnostics
Beyond signature checks, the report flags common claim timeline issues. It evaluates token expiry (exp), not-before activation (nbf), and suspicious issued-at timestamps (iat) to expose clock skew or token-minting defects that often cause authentication failures.
Security Boundaries
This tool verifies token integrity and claim shape, but it does not replace end-to-end authorization checks in your backend. Always enforce issuer, audience, scope, and revocation checks in production middleware even when signature validation succeeds.
Privacy Model
All token parsing and verification work is performed locally in your browser. JWT values, shared secrets, and public keys are not sent to remote services. This enables safer debugging for sensitive development and staging workflows.
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Frequently Asked Questions About JWT Debugger & Signature Verifier
The tool decodes JWT headers and payloads, validates compact token structure, and attempts signature verification based on header alg. It also highlights common claim timing issues such as expired exp claims, not-yet-active nbf values, and suspicious iat drift.
It supports HMAC algorithms HS256, HS384, HS512 with shared-secret input, RSA algorithms RS256, RS384, RS512 with public key PEM, and ECDSA algorithms ES256, ES384, ES512 with public key PEM plus JOSE signature adaptation for verification.
For HS* tokens you need the original shared secret. For RS* and ES* tokens you need the corresponding public key in PEM format. If key material is missing, the tool still decodes the token but reports that signature verification could not be completed.
Yes, it handles alg=none semantics. Tokens with alg=none are considered structurally valid only when the signature segment is empty. Any non-empty signature segment with alg=none is flagged as inconsistent and potentially unsafe.
No. This tool helps debug token integrity and claim content, but production systems must still enforce issuer, audience, scope, and revocation checks server-side. Signature validity alone does not guarantee authorization correctness.
Yes. JWT decoding and signature verification run in your browser through Web Crypto APIs. Tokens, secrets, and keys are not uploaded to external servers, making the workflow suitable for sensitive debugging sessions.
Yes. JWT Debugger & Signature Verifier is free and does not require signup. You can run unlimited token inspections and signature checks for development, testing, and operational troubleshooting workflows.