Free Online JWT Debugger & Token Inspector
Free online JWT debugger and decoder. Inspect headers, claims, and payload data. Verify HMAC-SHA256 signatures with Web Crypto and audit expiration times with 100% privacy.
{
"alg": "HS256",
"typ": "JWT",
"kid": "super-toolkit-k1"
}{
"iss": "https://auth.supertoolkit.app/",
"sub": "usr_0h8f3291ad",
"aud": [
"https://api.supertoolkit.app/"
],
"iat": 1729498000,
"exp": 1800000000,
"nbf": 1729498000,
"scope": "read:profile write:converters",
"email": "engineer@example.com",
"email_verified": true,
"roles": [
"admin",
"developer"
]
}Issued At (iat)
Mon, 21 Oct 2024 08:06:40 GMT
Not Before (nbf)
Mon, 21 Oct 2024 08:06:40 GMT
Expires At (exp)
Fri, 15 Jan 2027 08:00:00 GMT
How to Use JWT Debugger & Token Inspector
Paste Encoded JWT Token
Paste your Bearer token or select a sample preset. The token decodes instantly in your browser with zero network requests.
Inspect Claims & Expiration
Audit decoded header parameters, payload claims (sub, iss, aud), and live expiration countdown timers.
Verify HMAC Signature or Edit
Enter your secret key to verify the HS256 signature locally using Web Crypto, or edit claims to generate a newly encoded token.
Why Use This Tool?
Concrete Input & Output Walkthroughs
Enables instant auditing of user permissions, scopes, and expiration without transmitting bearer tokens to third-party debuggers.
How Industry Professionals Use JWT Debugger & Token Inspector
Verifying user IDs, tenant identifiers, and custom claims in Supabase, Firebase, or Auth0 tokens during local API testing.
Auditing authentication tokens for algorithm downgrade vulnerabilities (alg: "none") or weak signing secrets.
Technical Specifications & Architecture
Native Web Crypto API (crypto.subtle.sign) & RFC 7519 Base64Url Engine
Splits dot-delimited segments, applies base64url decoding, parses JSON AST, and performs HMAC-SHA256 signature verification in hardware-accelerated Web Crypto.
Zero network requests. Secret keys and confidential JWTs never leave the local browser heap.
100% Client-side. No tokens or secrets are ever transmitted to any remote servers.
Real Constraints & Practical Workarounds
Unlike competitors who promise unlimited capabilities without technical details, Super ToolKit believes in full engineering transparency:
Asymmetric algorithms (RS256, ES256) require a public certificate (PEM or JWKS URL) rather than a shared symmetric secret.
JWT Debugger & Token Inspector vs Cloud Converters
Why wait in server queues or risk confidential documents? Super ToolKit processes JWT Debugger & Token Inspector on-device in your browser.
| Provider | Uploads files? | Max file size | Signup required? | Works offline? | Watermark? | Data Privacy & Retention |
|---|---|---|---|---|---|---|
JWT Debugger & Token Inspector (Super ToolKit)Recommended | No (0 bytes uploaded) | No limit (RAM only) | No signup – 100% free | Yes (Offline PWA) | None | 100% private in-browser memory, 0 server logs |
| Convertio | Yes – uploads files to remote cloud servers (AWS) | 100 MB free cap (larger files require paid plan) | Required for files >100 MB & high batch count | No – completely fails without active internet | None on basic conversions | Files retained on remote server for 24 hours |
| CloudConvert | Yes – transmits data to centralized conversion nodes | Capped at 25 conversion credits / day on free tier | Mandatory after daily quota is exhausted | No – requires constant internet connection | None | Stored temporarily in cloud bucket before deletion |
| 123apps | Yes – uploads media to remote servers for processing | 700 MB free tier limit with daily operation quotas | Required for larger limits & ad removal | No – relies entirely on server round-trips | None, but heavy ad interruptions | Uploaded to cloud storage, deleted after processing |
| Zamzar | Yes – streams files to remote conversion infrastructure | 50 MB free file limit; max 2 conversions per 24 hours | Required for files over 50 MB and batch conversions | No – fails offline | None | Files held on server; download links sent via email |
| FreeConvert | Yes – requires uploading entire file over the wire | 1 GB free limit, but throttled to 25 conversion minutes/day | Required to bypass daily conversion minute limits | No – unusable without broadband connection | None | Hosted on remote servers for up to 6 hours |
Zero Latency & Zero Bandwidth Waste
Traditional tools force you to upload large multi-megabyte files across the internet to their servers, wait in a background queue, encode on their hardware, and download the output. Super ToolKit reads the file directly from your local RAM via JavaScript and WebAssembly, eliminating the upload and download cycles completely.
Absolute Privacy by Physical Design
Cloud services rely on written privacy policies promising they delete files after 24 hours. Super ToolKit relies on physical computer architecture: your data never touches a network packet to an external processing server. Even if someone intercepted our traffic, your files simply are not there.
Immune to Server Downtime & Offline Ready
When competitor cloud servers experience traffic spikes or maintenance windows, their queue freezes. Super ToolKit runs on your local CPU and GPU threads. You can disconnect your internet cable or turn on Airplane Mode, and the tool continues functioning seamlessly.
No Artificial Monetization Friction
Because cloud providers pay massive Amazon AWS bills for compute servers and bandwidth, they are forced to impose arbitrary 50MB/100MB file caps, 25-conversions-per-day quotas, and aggressive paid subscription upsells. Super ToolKit has zero server compute costs, meaning we never need to gatekeep your productivity.
Are my tokens or secret keys sent to a remote server?
No. Super ToolKit runs 100% in your browser. All JWT decoding and HMAC-SHA256 cryptographic signature checks are executed strictly in local memory using the native Web Crypto API.
How do I verify the HMAC-SHA256 signature of my JWT?
Paste your secret key into the verification input. The tool uses crypto.subtle.sign to compute the expected HMAC hash and verifies that it matches the token signature in milliseconds.
Can this tool decode tokens with asymmetric algorithms like RS256 or ES256?
Yes. It will decode and inspect the header and payload claims for all JWT algorithms, and will indicate when an asymmetric public key certificate is required for signature verification.
Can I edit claims and generate a new token?
Yes. Click "Edit Claims" to modify JSON properties directly, and the tool will immediately re-encode the Base64Url segments.