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.
git clone --depth 1 https://github.com/d-padmanabhan/agent-engineering-handbookWrote 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.
[](https://agentmods.dev/rules/d-padmanabhan/agent-engineering-handbook/225-javascript-typescript)<a href="https://agentmods.dev/rules/d-padmanabhan/agent-engineering-handbook/225-javascript-typescript"><img src="https://agentmods.dev/badge/rules/d-padmanabhan/agent-engineering-handbook/225-javascript-typescript/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.
<a href="https://agentmods.dev/rules/d-padmanabhan/agent-engineering-handbook/225-javascript-typescript"><img src="https://agentmods.dev/badge/rules/d-padmanabhan/agent-engineering-handbook/225-javascript-typescript.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00000 | $0.00836 |
| Opus 5.5 | $0.00000 | $0.00334 |
| Sonnet 5.5 | $0.00000 | $0.00167 |
| Haiku 4.5 | $0.00000 | $0.00084 |
Grade A, and why
225-javascript-typescript scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 66 lines — stays where its author put it; the contents beside it link to each section on GitHub.
JavaScript and TypeScript Engineering Gates
This rule owns mandatory policy only. Use the TypeScript and JavaScript skill (${HANDBOOK_ROOT}/skills/typescript-javascript/SKILL.md) for language patterns, configuration, testing, performance, and examples.
Shared Runtime and Supply-Chain Gates
- Pin the supported Node.js runtime and package-manager version. Use the committed lock file with immutable CI installation.
- Do not use
eval,Function, unsafe deserialization, or shell-interpreted command strings with untrusted input. - Validate external data at runtime before assigning domain types. Type declarations do not validate JSON, environment variables, messages, storage, or request bodies.
- Keep secrets out of source, browser bundles, logs, errors, command arguments, and committed configuration.
- Use ESM unless repository compatibility requires another module format; do not mix module systems accidentally.
HTTP and Server Gates
- Reuse clients or agents where the runtime supports pooling. Every outbound request requires a timeout or abort signal, status handling, bounded body processing, and runtime response validation.
- Validate URLs and constrain outbound destinations when input can influence a fetch. Do not follow redirects into untrusted networks without revalidation.
- Servers require bounded request bodies, explicit CORS policy, security headers, structured error handling, timeouts, and graceful shutdown.
- Authentication and authorization are separate. Enforce resource authorization on the server for every protected operation.
- Await or deliberately supervise every promise. Fire-and-forget work requires explicit lifecycle ownership and error reporting.
Use the observability skill
(${HANDBOOK_ROOT}/skills/observability/SKILL.md) for structured event schemas,
redaction, metrics, trace propagation, SLOs, alerts, and telemetry pipelines.
JavaScript Gates
- Production JavaScript uses
// @ts-checkand JSDoc types unless the repository documents an alternative static-analysis contract. - Exported JavaScript APIs document parameter, return, callback, generic, and shared object types with precise JSDoc.
- Do not silence type errors with broad
@ts-ignore; use a narrow@ts-expect-erroronly with a reason and a testable compatibility boundary. - Treat JSDoc assertions as compile-time aids, never as runtime validation.
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 Changed · +4 lines 4d4e8dcd70e3
- 1mo ago First seen · 62 lines · 0 tokens per session scan A c3babaef8e0d
225-javascript-typescript is a cursor rule published in the GitHub repository d-padmanabhan/agent-engineering-handbook (19 stars, last pushed 2d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 836 tokens. 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 2026-08-30.
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