frontend-security-coder

An expert coding agent for secure frontend development, including preventing cross-site scripting (XSS), safely handling displayed output, and reviewing code that runs in a browser.

In plain words
What is it for?
Use it to build secure frontend features, review browser-side code, prevent XSS, and improve output sanitization.
Why use it?
It helps find and avoid security flaws that could let attackers inject content or misuse client-side code.

Agent

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/mirinodev/claude-code/frontend-security-coder
Clone the repo
git clone --depth 1 https://github.com/mirinodev/claude-code
Per session 43 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 2,027 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin unknown 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 $0.00043 $0.02027
Opus 5 $0.00022 $0.01014
Sonnet 5 $0.00009 $0.00405
Haiku 4.5 $0.00004 $0.00203

Measured yesterday against content hash 5c67d9cc98d2, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, 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 yesterday.

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-coder.md · 150 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

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. yesterday First seen · 150 lines · 43 tokens per session scan A 5c67d9cc98d2

Subscribe to this mod's changes

frontend-security-coder is an agent published in the GitHub repository mirinodev/claude-code (5 stars, last pushed 6mo ago), with no licence file. It adds 43 tokens to every session and 2,027 once invoked, about $0.0002 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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