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JWT Signature Verifier

Verify JWT signatures (HMAC) and validate claims — all client-side.

Use JWT Workbench

JWT Token

Secret Key (for HMAC verification)

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JWT Signature Verifier: complete usage guide

Verify JWT HMAC signatures and inspect token claims locally to speed up authentication debugging without external services.

What this tool does

It decodes JWT header and payload segments for readable inspection.

It verifies HS256, HS384, and HS512 signatures using a provided secret key.

It evaluates common claims such as exp, nbf, iat, iss, aud, and sub.

It highlights signature validity and claim-status context for faster triage.

Typical use cases

Debug invalid token incidents across staging and production.
Validate shared-secret configuration during auth integration.
Review token claim windows for expiration or not-before issues.
Capture token diagnostics for support or incident reports.
Cross-check JWT payload shape before backend log deep-dives.

Input examples

JWT input

eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiIxMjMifQ.signature

Secret input

your-hmac-secret

Claim check

exp and nbf timestamps in payload

Output examples

Signature result

Signature Valid (HS256)

Decoded payload

{ "sub": "123", "exp": 1760000000, ... }

Claims panel

exp valid, nbf valid/invalid, iat info, issuer and audience values

Common errors and fixes

Token has invalid segment count

Ensure token includes header.payload.signature format.

Unsupported algorithm in token header

Use HS256/HS384/HS512 for this verifier mode.

Signature marked invalid unexpectedly

Verify secret value, whitespace, and exact token input.

Claim times appear wrong

Interpret epoch times in UTC and compare against current clock.

Decode succeeds but verify fails

Remember decoding does not imply signature validity.

Security and privacy notes

Verification runs in-browser and keeps token analysis local.
Do not paste production secrets into shared environments.
Redact user identifiers when sharing decoded claim snapshots.

Step-by-step workflow

Start with a minimal input for JWT Signature Verifier and verify baseline behavior first.
Make assumptions explicit: encoding, delimiter strategy, and timezone.
Change one variable at a time and compare output diffs.
Keep one verified output snapshot as a team reference.

Quality checklist before sharing output

Confirm JWT Signature Verifier output is deterministic across repeated runs with identical input.
Check boundary inputs (empty values, long fields, invalid characters).
Remove sensitive data before sharing output externally.
Verify final rendering on both desktop and mobile viewports.