frontend-security-reviewer

frontend-security-reviewer is an agent for Claude Code from NYTC69/review-loop. It costs 25 tokens per session (858 once invoked), scanned A, original, Apache-2.0.

An agent that checks changed frontend code for common web security vulnerabilities before a commit or pull request. Frontend code is the part of an application that runs in a user's browser.

In plain words
What is it for?
Use it to inspect changed JavaScript, TypeScript, HTML, CSS, Vue, or Svelte files and report security issues by severity.
Why use it?
It can reveal unsafe handling of browser content, commands, queries, and credentials before those issues reach users.

Agent for Claude Code

Written for Claude Code: shipped in a Claude Code plugin. Also seen: model in frontmatter.

Part of the review-loop plugin — 7 skills, 12 agents shipped together

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 agents/nytc69/review-loop/frontend-security-reviewer
Clone the repo
git clone --depth 1 https://github.com/NYTC69/review-loop

Made for: Claude Code.

Or install review-loop, the plugin that ships this one along with the rest of its 7 skills, 12 agents.

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-reviewer

README.md
[![agentmods](https://agentmods.dev/badge/agents/nytc69/review-loop/frontend-security-reviewer.svg)](https://agentmods.dev/agents/nytc69/review-loop/frontend-security-reviewer)
Your own site
<a href="https://agentmods.dev/agents/nytc69/review-loop/frontend-security-reviewer"><img src="https://agentmods.dev/badge/agents/nytc69/review-loop/frontend-security-reviewer.svg" alt="Measured on agentmods" height="20"></a>
Per session 25 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 858 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 $0.00025 $0.00858
Opus 5 $0.00013 $0.00429
Sonnet 5 $0.00005 $0.00172
Haiku 4.5 $0.00003 $0.00086

Measured 6d ago against content hash 0e01f790a408, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

frontend-security-reviewer 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.

agents/frontend-security-reviewer.md · 103 lines

How it starts

The opening of the file, as written. The whole thing — 103 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Frontend Security Review

MANDATORY: You MUST use the Read tool to read every file in scope BEFORE producing any analysis. Do NOT guess or fabricate file contents. If a file cannot be read, report the failure — do not invent its content.

Analyze changed frontend files for web security vulnerabilities, categorize issues by severity, and provide a clear verdict. This agent performs code-level analysis — no external CLI tools required.

Process

Step 1: Identify scope

If the task specifies a target path, use it. Otherwise, find changed frontend files:

git diff --name-only --diff-filter=d HEAD | grep -E '\.(ts|tsx|js|jsx|html|vue|svelte|css)$'

If no changed files found, report that no frontend files were changed and APPROVE.

Step 2: Read and analyze each file

Read every file in scope. For each file, check for the following vulnerability categories:

XSS (Cross-Site Scripting)

  • innerHTML, outerHTML assignments with dynamic content
  • dangerouslySetInnerHTML in React
  • Unsanitized template literals injected into DOM
  • eval(), Function(), setTimeout(string), setInterval(string)
  • document.write(), document.writeln()

SQL Injection

  • String concatenation in SQL queries
  • Missing parameterized queries / prepared statements
  • Raw SQL in ORM calls (e.g., raw(), execute() with template strings)

CSRF (Cross-Site Request Forgery)

  • Missing CSRF tokens on state-changing requests (POST, PUT, DELETE)
  • State mutations via GET requests
  • Missing SameSite cookie attributes

SSRF / DNS Rebinding

  • Unvalidated URLs in fetch(), axios, XMLHttpRequest
  • User-supplied hosts or IPs passed to server-side requests
  • Missing URL allowlist validation

Port Hijacking

  • Hardcoded ports (e.g., :3000, :8080) without environment variable fallback
  • localhost / 127.0.0.1 bindings without env config

Resource Abuse

  • Missing rate limiting on API calls
  • Unbounded file uploads (no size/type restrictions)
  • No cost caps on third-party API calls (e.g., AI APIs)
  • Missing pagination on list endpoints or data fetches

Read the full file on GitHub · 103 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 · 103 lines · 25 tokens per session scan A 0e01f790a408

Subscribe to this mod's changes

frontend-security-reviewer is an agent published in the GitHub repository NYTC69/review-loop (3 stars, last pushed 3mo ago), licensed Apache-2.0. It adds 25 tokens to every session and 858 once invoked, about $0.0001 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 2026-08-31.

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