What Is a JWT?

A JSON Web Token (JWT) is a compact, URL-safe token format used for authentication and information exchange. It's the standard way modern APIs verify who you are without server-side sessions.

The Three Parts

Every JWT has three Base64url-encoded sections separated by dots:

  1. Header — specifies the algorithm (e.g., HS256, RS256) and token type
  2. Payload — contains claims like sub (subject), exp (expiration), iat (issued at), plus any custom data
  3. Signature — a cryptographic hash that verifies the token hasn't been tampered with

How Signing Works

With HMAC (HS256), the server signs the token with a shared secret. With RSA (RS256), it uses a private key — and anyone with the public key can verify it. The signature covers both the header and payload, so changing a single character invalidates the token.

Common Claims

  • iss — issuer (who created the token)
  • sub — subject (who the token is about)
  • exp — expiration time (Unix timestamp)
  • iat — issued at time
  • aud — audience (who the token is for)

Decode Any JWT Instantly

Use the JWT Decoder on CodeKitLab to paste any JWT and instantly see the header, payload, and signature — with expiration checking. Working with HMAC signatures? The HMAC Generator helps you create and verify them. Need to check a Unix timestamp from a JWT claim? Use the Unix Timestamp converter.

Security Best Practices

  • Never store secrets in the payload — it's Base64-encoded, not encrypted
  • Always validate the signature server-side
  • Set short expiration times and use refresh tokens
  • Use RS256 for distributed systems where multiple services verify tokens
  • Check the aud claim to prevent token misuse across services

JWTs power most modern authentication systems. Understanding their structure is essential for building and debugging secure APIs.

JWT-tokens avkodade

JWT bestar av tre delar: header, payload och signatur. De anvands for autentisering i moderna APIer. Avkoda alla JWT direkt med JWT Decoder. Kontrollera Unix-tidsstamplar med Unix Timestamp.

JWT-Tokens dekodiert

JWTs bestehen aus drei Teilen: Header, Payload und Signatur. Sie werden fur die Authentifizierung in modernen APIs verwendet. Dekodieren Sie JWTs sofort mit dem JWT Decoder. Prufen Sie Unix-Zeitstempel mit dem Unix Timestamp Konverter.

Tokens JWT decodes

Les JWT se composent de trois parties : header, payload et signature. Ils sont utilises pour l'authentification dans les APIs modernes. Decodez tout JWT avec le JWT Decoder. Verifiez les horodatages Unix avec Unix Timestamp.

Tokens JWT decodificados

Los JWT constan de tres partes: header, payload y firma. Se usan para autenticacion en APIs modernas. Decodifica cualquier JWT con el JWT Decoder. Verifica marcas de tiempo Unix con Unix Timestamp.

فك تشفير توكنات JWT

تتكون JWT من ثلاثة أجزاء: الرأس والحمولة والتوقيع. تُستخدم للمصادقة في واجهات API الحديثة. فك تشفير أي JWT باستخدام JWT Decoder. تحقق من الطوابع الزمنية باستخدام Unix Timestamp.

JWT ٹوکنز ڈی کوڈ

JWT تین حصوں پر مشتمل ہوتے ہیں: ہیڈر، پے لوڈ اور دستخط۔ یہ جدید APIs میں تصدیق کے لیے استعمال ہوتے ہیں۔ JWT Decoder سے کوئی بھی JWT ڈی کوڈ کریں۔ Unix Timestamp سے ٹائم اسٹیمپ چیک کریں۔