JWT Decoder
Decode JSON Web Tokens (JWT) locally, inspect Header & Payload claims, and check expiration status instantly.
JWT Decoder
Decode and inspect JSON Web Tokens locally. Check expiration & claims privately.
{
"alg": "HS256",
"typ": "JWT",
"kid": "key_01"
}{
"sub": "usr_94810293",
"name": "Jane Developer",
"role": "admin",
"email": "jane@example.com",
"iat": 1774000000,
"exp": 2524608000
}Signature string present (sample_signature...). To verify signature authenticity, use your server secret key or public key.
Educational Purpose Disclaimer
This calculator is provided for informational and educational estimation purposes only. All calculations and projections are based on standard mathematical formulas and assumed inputs. The output values should not be considered professional financial, legal, tax, or medical advice. ProCalc is not a registered financial advisor or licensed practitioner. Always consult a qualified professional (such as a Chartered Accountant, certified planner, or physician) before making major decisions.
What is the JWT Decoder?
The JWT Decoder is a secure, browser-only tool for decoding and inspecting JSON Web Tokens (JWTs). Used universally across modern web applications, OAuth 2.0, OpenID Connect (OIDC), and API authentication, JWTs store encoded claims in a compact three-part string separated by dots: Header, Payload, and Signature.
Developers frequently need to inspect the contents of a JWT to check user roles, permissions (`scope`), issuer (`iss`), subject (`sub`), issued-at time (`iat`), and expiration (`exp`). This tool decodes your token instantly, validates claim structure, and highlights expiration status in real time.
Why Local Client-Side Decoding Is Crucial
JSON Web Tokens often contain sensitive user emails, user IDs, organizational permissions, session flags, and sometimes authorization bearer tokens. Sending JWTs to an untrusted third-party server exposes your user credentials and session tokens to potential logging or intercept attacks.
Our JWT Decoder decodes tokens entirely in your browser using client-side Base64URL decoding — no network requests are ever made.
Key Features
- Instant Header & Payload Parsing: Separates algorithm (`alg`), key ID (`kid`), payload claims, and signature.
- Real-Time Expiration Check: Automatically converts Unix `exp` and `nbf` timestamps into human-readable local/UTC dates and calculates remaining token lifespan.
- Status Badges: Shows ACTIVE, EXPIRED, or NOT YET VALID status badges with countdown timer.
- Formatted JSON View: Formats parsed header and payload as clean, highlighted JSON with one-click copy.
- Sample Token Generator: Load pre-configured sample JWTs to test the decoder.
How Does the JWT Decoder Work?
1. Paste your JWT string (`eyJhbGciOi...`) into the input box.
2. View Automatic Breakdown:
- Header (Red): Algorithm, token type, key ID.
- Payload (Purple): Claims, roles, user ID, expiration.
- Signature (Cyan): Cryptographic signature verification status.
3. Check Expiration: Inspect the token status badge (Active vs Expired) and remaining time.
4. Copy Output: Click Copy Payload or Copy Header as formatted JSON.
Formula & Calculation Method
JWT Structure:
Token = Header (Base64Url) + "." + Payload (Base64Url) + "." + Signature
Expiration Calculation:
Remaining Time = Token.exp (seconds) - (Date.now() / 1000)
If Remaining Time > 0 => Status = ACTIVE
If Remaining Time <= 0 => Status = EXPIRED
Example Calculation
Sample Payload Claim:
```json
{
"sub": "usr_94810293",
"name": "Jane Developer",
"role": "admin",
"iat": 1774000000,
"exp": 1774003600
}
```
- Issued At (iat): 2026-03-19 12:00:00 UTC
- Expires At (exp): 2026-03-19 13:00:00 UTC
- Lifespan: 1 hour (3,600 seconds)
Frequently Asked Questions
**JWT Structure:** Token = Header (Base64Url) + "." + Payload (Base64Url) + "." + Signature **Expiration Calculation:** Remaining Time = Token.exp (seconds) - (Date.now() / 1000) If Remaining Time > 0 => Status = ACTIVE If Remaining Time <= 0 => Status = EXPIRED
Disclaimer: This tool is provided for informational and calculation purposes. Output values are estimates based on standard user inputs.