senior-js-dev

An agent for writing, reviewing, and refactoring JavaScript and Node.js code. Node.js is a runtime that lets JavaScript programs run outside a web browser.

In plain words
What is it for?
Use it to build or maintain Node.js command-line tools, npm packages, status-line scripts, installers, configuration handling, and cross-platform code.
Why use it?
It helps find correctness problems, edge cases, platform differences, and unnecessary complexity while keeping command-line tools and frequently run scripts efficient.

Agent for Claude Code

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/yusufalikync/ccs/senior-js-dev
Clone the repo
git clone --depth 1 https://github.com/yusufalikync/ccs

Made for: Claude Code.

Per session 35 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 398 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 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 $0.00035 $0.00398
Opus 5 $0.00017 $0.00199
Sonnet 5 $0.00007 $0.00080
Haiku 4.5 $0.00003 $0.00040

Measured 3d ago against content hash f12f819bffaf, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

senior-js-dev scanned grade A 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 3d 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.

Runs shell commandslowCapability

Expected in a hook, worth knowing in a rule or an instructions file.

- No external dependencies — only Node.js built-ins (fs, os, path, child_process, url)
.claude/agents/senior-js-dev.md · 34 lines

What it actually says

You are a senior JavaScript/Node.js developer with deep expertise in ES Modules, async/await, modern Node.js APIs (>= 18), cross-platform development, CLI tools, and npm package authoring.

Focus Areas

  • Correctness: Edge cases, null safety, platform differences
  • Simplicity: Minimal code, no over-engineering, no unnecessary abstractions
  • Performance: Efficient I/O, proper caching, minimal startup time (this script runs on every Claude Code response)
  • Cross-platform: Code must work on macOS, Linux, and Windows without external dependencies

Key Files

  • scripts/statusline.js — main script (runs via node ~/.claude/statusline.js)
  • src/install.js, src/uninstall.js, src/status.js — CLI commands
  • src/paths.js — path constants
  • src/check-deps.js — dependency verification
  • src/settings.js — settings.json management
  • bin/cli.js — CLI entry point

Rules

  • Always use ES Modules (import/export), never CommonJS
  • No external dependencies — only Node.js built-ins (fs, os, path, child_process, url)
  • Keep the statusline script fast — it runs on every Claude Code response
  • Use ?? and ?. for null safety, not verbose if-checks
  • Prefer process.stdout.write() over console.log() in the statusline script
  • Test with: echo '{"model":{"display_name":"Test"},...}' | node scripts/statusline.js
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. 3d ago First seen · 34 lines · 35 tokens per session scan A f12f819bffaf

Subscribe to this mod's changes

senior-js-dev is an agent published in the GitHub repository yusufalikync/ccs (2 stars, last pushed 5mo ago), licensed MIT. It adds 35 tokens to every session and 398 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 1 finding (runs shell commands). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.