JWT Decoder vs Verifier
JWT decoding and JWT verification solve different problems. Separating their roles speeds up 401/403 troubleshooting.
Role difference (check this first)
- JWT Decoder: makes header/payload readable; does not prove signature validity.
- JWT Verifier: validates signature, keys, alg, kid, iss, and aud for authenticity.
- Conclusion: use verifier results for authz decisions.
Symptom-first entry points
- Need to inspect exp/nbf/iat quickly → Decoder
- Suspect invalid signature or key-rotation mismatch → Verifier
- Unknown 401/403 cause → 401/403 guide → Authorization / WWW-Authenticate
Recommended 401/403 flow
- 1) Read claims with Decoder (exp/nbf/aud/iss/scope)
- 2) Validate signature and key alignment with Verifier (alg/kid)
- 3) Use 401/403 guide to isolate HTTP header-side causes
Practical comparison axes
- Goal: Decoder for visibility, Verifier for validation
- Input: Decoder needs token only, Verifier also needs keys/JWKS and validation constraints
- Next step on failure: Decoder failure → format check, Verifier failure → key/alg/iss/aud checks
- Usage stage: Decoder for first-pass check, Verifier for production decisions
Inputs to collect before investigation
- Authorization header from failed requests (masked)
- WWW-Authenticate response (for 401 cases)
- Verification key material (secret/public key/JWKS)
- Expected iss/aud/scope values and environment time
Operational playbook (short)
- 401 spike: check signature failure rate and kid mismatch in Verifier first
- 403 spike: inspect scope/role claim changes in Decoder
- Suspected timing issue: compare exp/nbf with server NTP sync status
- Prevention: standardize reason codes in logs for 401 and 403
Related tools
Common mistakes
- Treating decoded output as proof of a valid token
- Verifying signature only and skipping aud/iss validation
- Ignoring WWW-Authenticate and checking only app logic on 401
Implementation checklist
- Whitelist allowed alg values and reject none/unexpected algorithms
- Manage iss/aud expectations in config to avoid environment drift
- Provide overlap window for old keys during key rotation
- Minimize token logging and avoid persisting sensitive claims
- Base authorization on verification outcomes, not decoded visibility
FAQ
- Is decoding claims enough for production checks?
- No. Authenticity decisions require Verifier checks for signature, keys, and iss/aud.
- What is the fastest check when Verifier fails?
- Check alg/kid alignment, active keys, iss/aud, then exp/nbf with clock skew in that order.
Referenced specs
Next to view (diagnostic order)
These links are generated from site_map rules in recommended diagnostic order.
- JWT Decoder — Decode and pretty-print JWT header/payload
- JWT Verifier — Verify JWT signatures (HS/RS/ES)
- JWT 401/403 Troubleshooting — Troubleshoot 401/403 auth failures from headers and JWT claims
- Authorization Inspect — Parse Authorization header formats
- WWW-Authenticate Inspect — Parse WWW-Authenticate challenges