JWT Beginner Guide — Start Here

Introduction

JSON Web Tokens (JWTs) are the standard for stateless authentication in modern APIs. This guide takes you from zero to confidently working with JWTs.

Step 1: Decode a Token

Paste any JWT into our JWT Decoder. You'll see three parts: header, payload, signature.

Step 2: Understand Claims

Registered claims: iss, sub, aud, exp, nbf, iat, jti. Custom claims carry app-specific data.

Step 3: Create Your First Token

// Node.js
const jwt = require('jsonwebtoken');
const token = jwt.sign(
  { sub: 'user-42', role: 'user' },
  process.env.JWT_SECRET,
  { expiresIn: '1h', issuer: 'my-app' }
);

# Python
import jwt
from datetime import datetime, timedelta
token = jwt.encode(
    {'sub': 'user-42', 'exp': datetime.utcnow() + timedelta(hours=1)},
    secret, algorithm='HS256'
)

Step 4: Verify on Every Request

Never trust decoded payload without signature verification. Always verify with the correct key and algorithm.

Next Steps

Continue with our JWT Learning Path or read JWT Authentication Explained.

Understanding JWT Beginner Guide — Start Here in Production

Developers search for JWT Beginner Guide — Start Here when building API authentication with JSON Web Tokens. JWTs are used by OAuth 2.0, OpenID Connect, Auth0, Firebase, AWS Cognito, and Keycloak. Always validate exp, iss, and aud server-side — decoding alone proves nothing about authenticity.

JWT Structure Recap

Every JWT has three dot-separated segments: header (algorithm), payload (claims), signature (proof). Use JWT Decoder to inspect and JWT Validator to verify before trusting any claim value in production code.

Common Pitfalls

• Algorithm confusion (none attack) — whitelist allowed algorithms
• Secrets in the payload — payload is only Base64-encoded, not encrypted
• Ignoring clock skew on exp and nbf
• Weak HMAC secrets — use 256-bit random keys
• Skipping signature verification — always call verify(), not decode()
• Storing tokens in localStorage — XSS can steal them

Further Reading

Browse related resources: JWT Decoder, JWT Validator, JWT Basics, JWT Authentication, JWT Errors, Algorithms, Glossary, and Learning Path.