HTML Encoding Tips — Security and Best Practices

HTML Encoding Tips

Proper HTML encoding is critically important for the security and correctness of web applications.

Tip 1: Always Encode User Input

Any data received from users must be encoded before being inserted into HTML. This is the primary defense against XSS attacks.

Tip 2: Context Matters

Encoding for HTML content differs from encoding for attributes, JavaScript, and CSS. Use the appropriate method for each context.

Tip 3: Do Not Decode Unnecessarily

If data is already encoded, do not decode it for re-encoding. This can create vulnerabilities.

Tip 4: Use Libraries

Do not write encoding manually. Use proven libraries for your programming language: htmlspecialchars in PHP, html.escape in Python.

Tip 5: Special Characters in Content

To insert characters like ©, ™, € use named entities: ©, ™, €. This is more reliable than directly inserting Unicode.

Tip 6: Verify the Result

After encoding, always check the result in a browser. Double encoding will display & instead of &.

Tip 7: Content Security Policy

HTML encoding is just one layer of defense. Use CSP headers for additional security.

See also: URL Encoding, Base64 Encoding, Binary Text