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Hsts

DevOps & Security
hsts

Hsts is an Agent Skill for devops & security published in the thedaviddias/Front-End-Checklist repository on GitHub: a SKILL.md instruction file an AI agent can load to do this task.

Use when reviewing HTTP response headers on any site that serves content over HTTPS.

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QUICK START

How to use this skill

Bring this guide into your coding agent with a prompt tailored to the tool you use.

  1. Open your project in Codex.
  2. Copy and paste the prompt below.
  3. Review files and risks before approving any action.
Prompt to paste
Inspect the Agent Skill at https://github.com/thedaviddias/Front-End-Checklist/blob/HEAD/skills/hsts/SKILL.md and all supporting files. Report provenance, permissions, scripts, dependencies, and security risks. Propose an exact installation into .agents/skills/hsts, but wait for my approval before writing files or running scripts.

Copying this prompt does not install or run the skill. Review third-party files before use.

Set an HSTS header

Without HSTS, an attacker on the same network can intercept the first HTTP request and strip TLS (SSL stripping), silently downgrading the connection before the browser ever sees a redirect.

Quick Reference

  • Set Strict-Transport-Security: max-age=31536000; includeSubDomains on all HTTPS responses
  • Use max-age=31536000 (1 year) minimum; HSTS preloading requires at least 1 year
  • Add includeSubDomains to protect all subdomains from downgrade attacks
  • Add preload only after testing — it is difficult to reverse and takes weeks to propagate
  • Never send the HSTS header over plain HTTP — only over HTTPS

Check

Check whether the server sends a Strict-Transport-Security header on all HTTPS responses, and verify the max-age, includeSubDomains, and preload directives are appropriate.

Fix

Add a Strict-Transport-Security header with max-age=31536000 and includeSubDomains to all HTTPS responses. Configure your web server or CDN to send this header, and validate it with curl or securityheaders.com.

Explain

Explain what HTTP Strict Transport Security (HSTS) is, how it prevents SSL stripping attacks, what the max-age and includeSubDomains directives do, and why the preload directive requires caution.

Code Review

Review server config, headers, forms, and integration points related to Set an HSTS header. Flag exact responses, cookies, or browser behaviors that violate the rule, and verify them against the effective production-like response.

For full implementation details, code examples, and framework-specific guidance, see references/rule.md.

Rule page: https://frontendchecklist.io/en/rules/security/hsts