# security-headers-configuration

Sets up HTTP security headers against XSS, clickjacking and MIME sniffing. Useful when hardening an app or preparing for an audit.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 438 installs · ★ 236
- Author: secondsky
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/secondsky/claude-skills/tree/HEAD/plugins/security-headers-configuration/skills/security-headers-configuration/SKILL.md
- Updated: 2026-10-20
- HTML: https://affpapa.org/en/nevibecode/skills/secondsky-security-headers-configuration

## What it does

This skill walks through the headers a browser checks on every request. It lists four core ones: HSTS with `max-age=31536000; includeSubDomains`, CSP `default-src 'self'`, `X-Frame-Options: DENY` and `X-Content-Type-Options: nosniff`. Then come the configs.

For Express it shows wiring up `helmet` and setting CSP directives: `defaultSrc`, `scriptSrc`, `styleSrc`, `imgSrc`, `connectSrc`, `fontSrc`, `frameAncestors`. For Nginx there is an `add_header` block covering HSTS, `Referrer-Policy`, `Permissions-Policy` and CSP. A six-item checklist closes the main file, and `references/python-apache.md` adds Flask, Flask-Talisman, `.htaccess` and a header testing script.

One thing to watch: the Express CSP sample puts `'unsafe-inline'` in both `scriptSrc` and `styleSrc`, which weakens XSS protection. In production that value is a reason to rewrite the policy around your own scripts. The skill points to Security Headers, Mozilla Observatory and CSP Evaluator for verification.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add secondsky/claude-skills --skill security-headers-configuration -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/security-headers-configuration/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/security-headers-configuration/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add secondsky/claude-skills --skill security-headers-configuration -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/security-headers-configuration/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add secondsky/claude-skills --skill security-headers-configuration -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/security-headers-configuration/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install secondsky/claude-skills security-headers-configuration
```

2. **Manually: put the files in place**
- File: `.github/skills/security-headers-configuration/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add secondsky/claude-skills --skill security-headers-configuration -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/secondsky/claude-skills --path plugins/security-headers-configuration/skills/security-headers-configuration
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/security-headers-configuration/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add secondsky/claude-skills --skill security-headers-configuration -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/secondsky/claude-skills/tree/HEAD/plugins/security-headers-configuration/skills/security-headers-configuration/SKILL.md

## When to use it
- set HSTS, CSP and X-Frame-Options on an Express app
- add security headers to Nginx with add_header
- roll out a Content Security Policy and test it before deploy
- block MIME sniffing and clickjacking before a security audit
- configure headers for Flask or Apache via .htaccess

## Example prompts
- set up HTTP security headers for my Express app
- add CSP and HSTS to my Nginx config
- check my security headers and tell me what's too permissive

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: eba6612f1f59dce0.

BEGIN THIRD-PARTY FILE eba6612f1f59dce0
````text
---
name: security-headers-configuration
description: Configures HTTP security headers to protect against XSS, clickjacking, and MIME sniffing attacks. Use when hardening web applications, passing security audits, or implementing Content Security Policy.
license: MIT
---

# Security Headers Configuration

Implement HTTP security headers to defend against common browser-based attacks.

## Essential Headers

| Header | Purpose | Value |
|--------|---------|-------|
| HSTS | Force HTTPS | `max-age=31536000; includeSubDomains` |
| CSP | Restrict resources | `default-src 'self'` |
| X-Frame-Options | Prevent clickjacking | `DENY` |
| X-Content-Type-Options | Prevent MIME sniffing | `nosniff` |

## Express Implementation

```javascript
const helmet = require('helmet');

app.use(helmet());

// Custom CSP
app.use(helmet.contentSecurityPolicy({
  directives: {
    defaultSrc: ["'self'"],
    scriptSrc: ["'self'", "'unsafe-inline'"],
    styleSrc: ["'self'", "'unsafe-inline'"],
    imgSrc: ["'self'", "data:", "https:"],
    connectSrc: ["'self'", "https://api.example.com"],
    fontSrc: ["'self'", "https://fonts.gstatic.com"],
    frameAncestors: ["'none'"]
  }
}));
```

## Nginx Configuration

```nginx
add_header Strict-Transport-Security "max-age=31536000; includeSubDomains; preload" always;
add_header X-Frame-Options "DENY" always;
add_header X-Content-Type-Options "nosniff" always;
add_header X-XSS-Protection "1; mode=block" always;
add_header Referrer-Policy "strict-origin-when-cross-origin" always;
add_header Permissions-Policy "geolocation=(), microphone=(), camera=()" always;
add_header Content-Security-Policy "default-src 'self'; script-src 'self'" always;
```

## Verification Tools

- [Security Headers](https://securityheaders.com/)
- [Mozilla Observatory](https://observatory.mozilla.org/)
- [CSP Evaluator](https://csp-evaluator.withgoogle.com/)

## Security Headers Checklist

- [ ] HSTS enabled with long max-age
- [ ] CSP configured and tested
- [ ] X-Frame-Options set to DENY
- [ ] X-Content-Type-Options set to nosniff
- [ ] Referrer-Policy configured
- [ ] Permissions-Policy disables unused features

## Additional Implementations

See [references/python-apache.md](references/python-apache.md) for:
- Python Flask security headers middleware
- Flask-Talisman library configuration
- Apache .htaccess configuration
- Header testing script

## Common Mistakes
````
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