JWT Decoder/ Client-side

Instantly decode JWT header and payload, view expiry and standard claims. Token never leaves your browser.

JWT Token

Fügen Sie oben einen JWT-Token ein, um ihn zu dekodieren.

Token verlässt niemals Ihren Browser.

Hat dieses Tool Ihr Problem gelöst?

Was ist ein JWT

Ein JWT (JSON Web Token) ist ein kompaktes, URL-sicheres Token-Format mit drei Teilen: Header (Algorithmus-Infos), Payload (Claims/Daten) und Signatur. Wird主要用于 zur Authentifizierung verwendet — der Server stellt ein JWT aus, der Client附iert es in Anfragen, und der Server verifiziert die Signatur ohne Datenbankabfragen.

JWT-Sicherheitsaspekte

Speichern Sie niemals sensible Daten (Passwörter, Kreditkarten) in JWT-Payloads — sie sind nur Base64-kodiert und für jeden lesbar. Die Signatur gewährleistet nur Datenintegrität, nicht Vertraulichkeit. Verwenden Sie immer HTTPS, setzen Sie合理e Ablaufzeiten (15 Minuten bis 1Stunde empfohlen) und implementieren Sie Refresh-Token-Rotation.

Code Examples

JavaScript (jsonwebtoken)
import jwt from 'jsonwebtoken';

// Sign
const token = jwt.sign(
  { sub: 'user_123', role: 'admin' },
  process.env.JWT_SECRET,
  { expiresIn: '1h' }
);

// Verify
const payload = jwt.verify(
  token, process.env.JWT_SECRET
);
Python (PyJWT)
import jwt

# Sign
token = jwt.encode(
    {"sub": "user_123", "exp": exp_ts},
    secret,
    algorithm="HS256"
)

# Verify
payload = jwt.decode(
    token, secret,
    algorithms=["HS256"]
)
Go (golang-jwt)
import "github.com/golang-jwt/jwt/v5"

// Sign
token := jwt.NewWithClaims(
  jwt.SigningMethodHS256,
  jwt.MapClaims{"sub": "user_123"},
)
signed, _ := token.SignedString(secret)

// Verify
parsed, _ := jwt.Parse(signed,
  func(t *jwt.Token) (any, error) {
    return secret, nil
  })
Decode only (any language)
// JWT = base64url(header)
//       + "."
//       + base64url(payload)
//       + "."
//       + signature

function decodeJwt(token) {
  const [h, p] = token.split('.');
  const decode = s => JSON.parse(
    atob(s.replace(/-/g,'+')
          .replace(/_/g,'/'))
  );
  return { header: decode(h),
           payload: decode(p) };
}

Frequently Asked Questions

What is a JWT?
JWT (JSON Web Token) is an open standard (RFC 7519) for securely transmitting information as a JSON object. It consists of three Base64URL-encoded parts separated by dots: Header (algorithm & token type), Payload (claims), and Signature.
Can a JWT be forged?
The payload is only Base64URL-encoded — anyone can decode and read it. However, the signature cannot be forged without the secret key. JWT security relies entirely on signature verification; sensitive data should not be stored in the payload unless you use JWE (encrypted JWT).
What are exp, iat, and nbf?
These are standard JWT claims: exp (Expiration Time) is when the token expires; iat (Issued At) is when it was issued; nbf (Not Before) means the token is invalid before that time. All timestamps are Unix time (seconds since epoch).
Why can't signature verification be done in the browser?
Verification requires the secret key (for HMAC algorithms) or public key (for RSA/ECDSA). In a pure frontend context, these keys are typically unavailable. Signature verification should always be performed server-side in production.
What's the difference between HS256 and RS256?
HS256 (HMAC-SHA256) uses a single shared secret for both signing and verification — suitable for single-service setups. RS256 (RSA-SHA256) uses a private key to sign and a public key to verify — better for microservices where the public key can be distributed safely.
Is my token safe to paste here?
Yes. This tool runs entirely in your browser with no network requests — your token never leaves your device. That said, for production tokens containing sensitive claims, exercise caution and rotate them if you suspect exposure.