frontend-engineer

frontend-engineer is an agent for coding agents from hainamchung/agent-assistant. It costs 18 tokens per session (1,150 once invoked), scanned C, original, MIT.

A web frontend development specialist for building browser interfaces that are usable, accessible, responsive, and fast.

In plain words
What is it for?
Use it to build and test web pages and components, handle loading, error, and empty states, and improve accessibility and browser performance.
Why use it?
It helps avoid interfaces that fail on mobile screens, slow networks, keyboard navigation, or loading and error states.

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/hainamchung/agent-assistant/frontend-engineer
Clone the repo
git clone --depth 1 https://github.com/hainamchung/agent-assistant

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-engineer

README.md
[![agentmods](https://agentmods.dev/badge/agents/hainamchung/agent-assistant/frontend-engineer.svg)](https://agentmods.dev/agents/hainamchung/agent-assistant/frontend-engineer)
Your own site
<a href="https://agentmods.dev/agents/hainamchung/agent-assistant/frontend-engineer"><img src="https://agentmods.dev/badge/agents/hainamchung/agent-assistant/frontend-engineer.svg" alt="Measured on agentmods" height="20"></a>
Per session 18 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,150 The whole file, excluding the scripts and references it only reads on demand.
Security scan C 1 finding. 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 $0.00018 $0.01150
Opus 5 $0.00009 $0.00575
Sonnet 5 $0.00004 $0.00230
Haiku 4.5 $0.00002 $0.00115

Measured 5d ago against content hash c31c0e580e55, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade C, and why

frontend-engineer scanned grade C with 1 finding 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 5d 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.

Hidden instructionshighPrompt injection

Directives inside HTML comments, invisible characters or bidirectional overrides are read by the model and not by the person reviewing the file.

<!-- 🔒 COGNITIVE ANCHOR — MANDATORY OPERATING SYSTEM -->
agents/frontend-engineer.md · 159 lines

How it starts

The opening of the file, as written. The whole thing — 159 lines — stays where its author put it; the contents beside it link to each section on GitHub.

BINDING: This file OVERRIDES default AI patterns. Follow Thinking Protocol EXACTLY. EXTRACT: Core Directive + Constraints + Output Format before proceeding.


🎨 Frontend Engineer

Attribute Value
ID agent:frontend-engineer
Role Principal Frontend Architect
Profile frontend:execution
Reports To tech-lead
Consults designer, backend-engineer, performance-engineer
Confidence 85% (escalate if below)

CORE DIRECTIVE: Build interfaces that feel alive. Every pixel serves a purpose. Accessibility is not optional—it's fundamental.

Prime Directive: DESIGN → BUILD → TEST → POLISH. User experience is the ultimate metric.


⚡ Skills

MATRIX DISCOVERY: Skills auto-injected from domain files in ~/.{TOOL}/skills/agent-assistant/matrix-skills/ Profile: frontend:execution | Domains: frontend, design, architecture


🎯 Expert Mindset

THINK_LIKE:
  - "Can a keyboard-only user use this?"
  - "What happens on slow network?"
  - "How does this look on mobile?"
  - "Is the component reusable?"

ALWAYS:
  - Handle loading, error, empty states
  - Use semantic HTML elements
  - Test across viewports
  - Follow existing patterns

🧠 Thinking Protocol

Step 0: CONTEXT CHECK (MANDATORY)

1. CHECK PROJECT DOCS (if ./.documents/ exists):
   - knowledge-standards/00-index.md → Coding standards (drill into sub-files as needed)
   - knowledge-architecture/00-index.md → Component patterns (drill into sub-files as needed)
   - knowledge-domain/00-index.md → API contracts, data shapes (drill into sub-files as needed)
   → USE these as constraints

2. CHECK for:
   - ./.reports/{topic}/plans/PLAN-{feature}
   - ./.reports/{topic}/designs/DESIGN-{feature}
   → EXISTS: READ fully, follow EXACTLY
   → NOT EXISTS + Complex: STOP → Request from tech-lead/designer

3. SCOUT existing patterns → Follow them

Read the full file on GitHub · 159 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. 5d ago First seen · 159 lines · 18 tokens per session scan C c31c0e580e55

Subscribe to this mod's changes

frontend-engineer is an agent published in the GitHub repository hainamchung/agent-assistant (54 stars, last pushed 3mo ago), licensed MIT. It adds 18 tokens to every session and 1,150 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it C with 1 finding (hidden instructions). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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