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JWT Authentication: A Complete Guide for Web Developers

JWT (JSON Web Token) is the standard for secure authentication in modern web applications.

What is a JWT?

A compact, URL-safe token with three parts: header.payload.signature

Header

Contains token type (JWT) and signing algorithm (HS256, RS256)

Payload

Contains claims (user data, permissions). Not encrypted - don't store sensitive data.

Signature

Verifies the token hasn't been tampered with.

🎫 Decode JWT Tokens →

How It Works

1. User logs in with credentials
2. Server validates and generates JWT
3. Client stores JWT
4. Client sends JWT with each request
5. Server verifies signature

Security Best Practices

• Use HTTPS always
• Set short expiration times
• Store tokens securely (httpOnly cookies)
• Implement token refresh
• Validate signature on every request
• Use strong secret keys (256+ bits)

Common Mistakes

• Storing sensitive data in payload
• No expiration time
• Weak secret keys
• Not validating tokens server-side
• Storing in localStorage (XSS vulnerable)

Debug JWTs with our JWT Decoder.

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