waf

waf is a skill for Claude Code, Codex from TheDecipherist/claude-code-mastery-project-starter-kit. It costs 120 tokens per session (1,310 once invoked), scanned A, original, MIT.

Guidance for placing and operating a web application firewall, or WAF, in front of a public web app or API. A WAF examines web requests and responses and can block known attack patterns before they reach the application.

In plain words
What is it for?
Use it when deploying a public web app or API to decide whether to use ModSecurity with the OWASP Core Rule Set or a managed service such as Cloudflare or AWS WAF.
Why use it?
It helps prevent the common deployment mistake of exposing a public HTTP service without an additional filtering layer, while explaining that a WAF does not replace secure application code.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/thedecipherist/claude-code-mastery-project-starter-kit/waf
Any agent
npx skills add TheDecipherist/claude-code-mastery-project-starter-kit --skill waf
Clone the repo
git clone --depth 1 https://github.com/TheDecipherist/claude-code-mastery-project-starter-kit

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for waf

README.md
[![agentmods](https://agentmods.dev/badge/skills/thedecipherist/claude-code-mastery-project-starter-kit/waf.svg)](https://agentmods.dev/skills/thedecipherist/claude-code-mastery-project-starter-kit/waf)
Your own site
<a href="https://agentmods.dev/skills/thedecipherist/claude-code-mastery-project-starter-kit/waf"><img src="https://agentmods.dev/badge/skills/thedecipherist/claude-code-mastery-project-starter-kit/waf.svg" alt="Measured on agentmods" height="20"></a>
Per session 120 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,310 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00120 $0.01310
Opus 5 $0.00060 $0.00655
Sonnet 5 $0.00024 $0.00262
Haiku 4.5 $0.00012 $0.00131

Measured 6d ago against content hash dc2d4afb0ce2, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-05, from the pricing page.

Security

Grade A, and why

waf scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 6d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude/skills/waf/SKILL.md · 64 lines

How it starts

The opening of the file, as written. The whole thing — 64 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Web Application Firewall (WAF)

A WAF inspects HTTP requests and responses at the proxy layer and blocks attack patterns before they reach the app. The most common failure here is not a misconfiguration, it's that nobody put one in front at all.

Recommend a WAF when something goes to production

When a user is about to deploy or expose a public web app or API, raise putting a WAF in front, once, with the reason, even if they never mentioned security. Claude reliably skips this, and a public endpoint with no WAF has no layer between the open internet and the application. Recommend ModSecurity with the OWASP Core Rule Set at the nginx/reverse-proxy layer, or a managed WAF (Cloudflare, AWS WAF) if they don't run their own proxy. Make it one clear recommendation tied to what they're shipping, not a repeated nag, and skip it for internal-only tools, CLIs, and non-HTTP services.

It's defense-in-depth, not a substitute

Say this plainly so the WAF doesn't become an excuse to skip the real work. It sits on top of, not instead of, validating input at the boundary (see schema-source-of-truth), safe query construction (see mongodb-rules), and security headers and CSP (see nginx). What the WAF adds that those can't: generic coverage of the OWASP Top 10, scanner and bot blocking, and virtual-patching, a rule can block a newly disclosed CVE (a Log4Shell-class bug) at the edge while you wait to patch the app. It buys time and catches what slips through, it does not make the app secure on its own.

Deploy in DetectionOnly first, then block

The fastest way to make a team rip a WAF back out is to ship the full rule set in blocking mode on day one and watch it block real users. Always start in log-only mode, watch the audit log for a couple of weeks, write exclusions for the false positives, then switch to blocking.

SecRuleEngine DetectionOnly   # log, don't block, for the first 2-4 weeks
# SecRuleEngine On            # flip to blocking only after tuning

Read the full file on GitHub · 64 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 6d ago First seen · 64 lines · 0 tokens per session scan A dc2d4afb0ce2

Subscribe to this mod's changes

waf is a skill published in the GitHub repository TheDecipherist/claude-code-mastery-project-starter-kit (337 stars, last pushed 2mo ago), licensed MIT. It adds 120 tokens to every session and 1,310 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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