A JavaScript and TypeScript coding mode for creating, changing, or reviewing code under documented safety, quality, and security rules.

Use it to write new JavaScript modules, modify existing code, or review JavaScript for correctness, security, and performance.

It gives coding tasks a defined set of checks for input validation, error handling, dependencies, secrets, and compatibility.

javascript — Command for Claude Code by d-padmanabhan

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.

Clone the repo

git clone --depth 1 https://github.com/d-padmanabhan/agent-engineering-handbook

Made for: Claude Code.

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.

README.md

[![agentmods](https://agentmods.dev/badge/commands/d-padmanabhan/agent-engineering-handbook/javascript/github.svg)](https://agentmods.dev/commands/d-padmanabhan/agent-engineering-handbook/javascript)

Your own site

<a href="https://agentmods.dev/commands/d-padmanabhan/agent-engineering-handbook/javascript"><img src="https://agentmods.dev/badge/commands/d-padmanabhan/agent-engineering-handbook/javascript/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.

Your own site · 80×15

<a href="https://agentmods.dev/commands/d-padmanabhan/agent-engineering-handbook/javascript"><img src="https://agentmods.dev/badge/commands/d-padmanabhan/agent-engineering-handbook/javascript.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 16 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.

When invoked 407 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe.

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.

Model	Per session	Once invoked
Fable 5.1	$0.00016	$0.00407
Opus 5.5	$0.00006	$0.00163
Sonnet 5.5	$0.00003	$0.00081
Haiku 4.5	$0.00002	$0.00041

Measured 1mo ago against content hash e4dd1bd06524, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

javascript 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 1mo 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.

- **Critical**: injection, SSRF, unsafe `child_process` usage, secrets in logs, auth/authz mistakes

commands/javascript.md · 64 lines

What it actually says

JAVASCRIPT MODE ACTIVATED

You are now in JAVASCRIPT MODE. Any work on JavaScript MUST follow:

rules/225-javascript-typescript.mdc (shared JavaScript/TypeScript safety and type gates)
rules/100-core.mdc (minimal, production-ready changes)
rules/310-security.mdc (no secrets, OWASP-minded)

Use this command when the user asks to:

Create new JS modules/functions
Modify existing JS code
Review JS code for correctness/security/performance

Guardrails (mandatory)

Prefer async/await; avoid callbacks unless required.
Validate external input; avoid injection in templating/queries/commands.
Avoid adding dependencies unless necessary.
Don’t log secrets; redact tokens/headers.

Step 0: Determine intent (create vs modify vs review)

Infer intent from the user’s request. If ambiguous, ask ≤3 clarifying questions (runtime, module system, build tooling, Node/browser target).

Create

Produce complete code with:

Clear exports
Error handling
JSDoc + @ts-check for production JavaScript (per 225-javascript-typescript.mdc)

Modify

Minimal diffs
Preserve behavior unless requested
Keep API compatibility unless requested to break it

Review

Prioritize:

Critical: injection, SSRF, unsafe child_process usage, secrets in logs, auth/authz mistakes
Recommended: performance hotspots, poor error handling, missing input validation
Optional: style/readability

Verification (as applicable):

pre-commit run --all-files

Done condition

End with:

Files changed (or “no changes made”)
How to validate (lint/tests/build) and expected behavior

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.

1mo ago First seen · 64 lines · 16 tokens per session scan A e4dd1bd06524

Subscribe to this mod's changes

javascript is a command published in the GitHub repository d-padmanabhan/agent-engineering-handbook (19 stars, last pushed 2d ago), licensed MIT. It adds 16 tokens to every session and 407 once invoked, about $0.0001 per session on Opus 5.5. 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 2026-08-30.

Languages TypeScript

javascript