# JWT & OAuth Token Debugger

> Private JWT Decoder & Signature Verifier | Privatools
> Canonical URL: [https://privatools.dev/tools/jwt-inspector/](https://privatools.dev/tools/jwt-inspector/)
> Markdown Alternate: [https://privatools.dev/tools/jwt-inspector.md](https://privatools.dev/tools/jwt-inspector.md)
> Execution Architecture: 100% Client-Side In-Memory Execution (Zero Remote Egress)

## Overview
Decode, edit, and cryptographically verify JSON Web Tokens (JWT) using the native browser Web Crypto API. Inspect headers, claims, expiration timestamps, and HMAC/RSA signatures without sharing secrets or tokens with third parties.

## Format Specifications
- **Category:** Security & Dev
- **Supported Formats:** `JWT`, `JWS`, `OAuth`, `OIDC`, `JSON`
- **Privacy Guarantee:** 0 bytes uploaded to remote servers. All computation executes locally in browser memory.
- **Compliance:** GDPR, HIPAA & SOC 2 Friendly (process sensitive payloads and PII directly on your local device).

## Technology Stack
- Web Crypto API (SubtleCrypto)
- Base64URL Buffer Streaming
- Reactive State Store
- Live Expiration Monitor

## How It Works
1. The JWT string is split into header, payload, and signature components and decoded via Base64URL decoders.
2. Standard claims (exp, nbf, iat, iss, aud, sub) are parsed and formatted into human-readable timestamps and countdowns.
3. For HMAC tokens (HS256/384/512), Web Crypto imports your secret key into a secure crypto key context and validates the SHA signature locally.
4. For asymmetric tokens (RS256), public PEM keys can be imported for local mathematical signature verification.

## Practical Use Cases
### Confidential Authentication Token Debugging
Inspect OAuth 2.0, OpenID Connect, and internal microservice session tokens without leaking enterprise user credentials to public websites.

### Token Expiration & Clock Skew Audits
Analyze token TTL, issued-at timestamps, and clock skew issues when debugging token refresh loops.

### Claim Modification & Mocking
Edit payload claims in real time and re-sign tokens with local test secrets for frontend unit testing and API mocking.

### Signature Algorithm Verification
Confirm tokens are correctly signed with expected cryptographic algorithms and not vulnerable to 'none' algorithm exploits.

## Frequently Asked Questions
### Why should I use this instead of jwt.io?
Public web token debuggers transmit tokens over the network, where browser extensions, proxies, or servers can intercept sensitive user identities or session credentials. Privatools operates strictly client-side with zero data uploads.

### Are my secret keys or tokens logged anywhere?
No. All signature validations execute in browser memory via window.crypto.subtle. No analytics or server logs exist.

### Which cryptographic algorithms are supported for verification?
It supports HS256, HS384, HS512, and RS256 using standard Web Crypto primitives.

## Related Tools
- [X.509 Certificate Inspector & Exporter](https://privatools.dev/tools/cert-inspector/)
- [Cryptographic Checksum & File Hash Studio](https://privatools.dev/tools/hash-studio/)
- [Text & Encoding Studio](https://privatools.dev/tools/text-converter/)

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*Privatools — 100% Client-Side Web Utilities. No tracking, no remote server processing.*