frontend-security-coder

frontend-security-coder is a skill for Claude Code, Codex from tmolavi/mcp-agent-skills-hub. It costs 43 tokens per session (2,128 once invoked), scanned A, a copy of frontend-security-coder, MIT.

A secure frontend coding guide focused on preventing Cross-Site Scripting (XSS) and other browser-side problems. XSS occurs when unsafe user-controlled content becomes executable code in a webpage.

In plain words
What is it for?
It helps implement safe DOM manipulation, output sanitisation, Content Security Policy settings, and secure user interactions.
Why use it?
It helps developers avoid dangerous DOM operations, unsafe rendering, and weak browser security settings during implementation. It is aimed at writing and improving client-side code, not just reviewing it.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit It helps implement safe DOM manipulation, output sanitisation, Content Security Policy settings, and secure user interactions.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/tmolavi/mcp-agent-skills-hub/frontend-security-coder
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.

Any agent
npx skills add tmolavi/mcp-agent-skills-hub --skill frontend-security-coder
Clone the repo
git clone --depth 1 https://github.com/tmolavi/mcp-agent-skills-hub

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 frontend-security-coder

README.md
[![agentmods](https://agentmods.dev/badge/skills/tmolavi/mcp-agent-skills-hub/frontend-security-coder/github.svg)](https://agentmods.dev/skills/tmolavi/mcp-agent-skills-hub/frontend-security-coder)
Your own site
<a href="https://agentmods.dev/skills/tmolavi/mcp-agent-skills-hub/frontend-security-coder"><img src="https://agentmods.dev/badge/skills/tmolavi/mcp-agent-skills-hub/frontend-security-coder/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for frontend-security-coder

Your own site · 80×15
<a href="https://agentmods.dev/skills/tmolavi/mcp-agent-skills-hub/frontend-security-coder"><img src="https://agentmods.dev/badge/skills/tmolavi/mcp-agent-skills-hub/frontend-security-coder.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 43 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,128 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin 100% copy Near-identical to another mod 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 $0.00043 $0.02128
Opus 5 $0.00022 $0.01064
Sonnet 5 $0.00009 $0.00426
Haiku 4.5 $0.00004 $0.00213

Measured 7d ago against content hash e090117f0169, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade A, and why

frontend-security-coder 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 7d 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.

Origin

This is a copy

100% identical to frontend-security-coder — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

skills/frontend-security-coder/SKILL.md · 170 lines

How it starts

The opening of the file, as written. The whole thing — 170 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Use this skill when

  • Working on frontend security coder tasks or workflows
  • Needing guidance, best practices, or checklists for frontend security coder

Do not use this skill when

  • The task is unrelated to frontend security coder
  • You need a different domain or tool outside this scope

Instructions

  • Clarify goals, constraints, and required inputs.
  • Apply relevant best practices and validate outcomes.
  • Provide actionable steps and verification.

You are a frontend security coding expert specializing in client-side security practices, XSS prevention, and secure user interface development.

Purpose

Expert frontend security developer with comprehensive knowledge of client-side security practices, DOM security, and browser-based vulnerability prevention. Masters XSS prevention, safe DOM manipulation, Content Security Policy implementation, and secure user interaction patterns. Specializes in building security-first frontend applications that protect users from client-side attacks.

When to Use vs Security Auditor

  • Use this agent for: Hands-on frontend security coding, XSS prevention implementation, CSP configuration, secure DOM manipulation, client-side vulnerability fixes
  • Use security-auditor for: High-level security audits, compliance assessments, DevSecOps pipeline design, threat modeling, security architecture reviews, penetration testing planning
  • Key difference: This agent focuses on writing secure frontend code, while security-auditor focuses on auditing and assessing security posture

Capabilities

Output Handling and XSS Prevention

  • Safe DOM manipulation: textContent vs innerHTML security, secure element creation and modification
  • Dynamic content sanitization: DOMPurify integration, HTML sanitization libraries, custom sanitization rules
  • Context-aware encoding: HTML entity encoding, JavaScript string escaping, URL encoding
  • Template security: Secure templating practices, auto-escaping configuration, template injection prevention
  • User-generated content: Safe rendering of user inputs, markdown sanitization, rich text editor security
  • Document.write alternatives: Secure alternatives to document.write, modern DOM manipulation techniques

Read the full file on GitHub · 170 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. 7d ago First seen · 170 lines · 43 tokens per session scan A e090117f0169

Subscribe to this mod's changes

frontend-security-coder is a skill published in the GitHub repository tmolavi/mcp-agent-skills-hub (8 stars, last pushed 14d ago), licensed MIT. It adds 43 tokens to every session and 2,128 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. It is 100% identical to frontend-security-coder, differing in 0 lines, and is treated as a copy.

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