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.
npx agentmods add skills/ccheney/robust-skills/modern-javascriptnpx skills add ccheney/robust-skills --skill modern-javascriptgit clone --depth 1 https://github.com/ccheney/robust-skillsWrote 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/skills/ccheney/robust-skills/modern-javascript)<a href="https://agentmods.dev/skills/ccheney/robust-skills/modern-javascript"><img src="https://agentmods.dev/badge/skills/ccheney/robust-skills/modern-javascript.svg" alt="Measured on agentmods" 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 | $0.00111 | $0.02551 |
| Opus 5 | $0.00056 | $0.01275 |
| Sonnet 5 | $0.00022 | $0.00510 |
| Haiku 4.5 | $0.00011 | $0.00255 |
Grade A, and why
modern-javascript 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 4d 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 — 182 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Modern JavaScript
Use current JavaScript without confusing specification status, runtime support, and toolchain support. Treat these as three separate questions:
- Is it standardized? Check the frozen annual ECMA-262 edition or TC39's current proposal tracker.
- Does the target run it? Check the project's declared Node/browser targets and current compatibility data.
- Can tooling bridge the gap? Syntax may need a transform; built-ins need a polyfill. One does not imply the other.
Workflow
- Inspect
package.json(engines,browserslist, dependencies), runtime/deployment config,tsconfig.json, and Babel/bundler config. Do not invent a baseline. - Select the simplest standardized feature supported by that baseline.
- For a newer standard or mature proposal, state the required runtime, transform, or polyfill in the implementation or handoff.
- Preserve observable behavior while modernizing: mutation, evaluation order, iterator consumption, concurrency, cancellation, property descriptors, and error propagation matter more than shorter syntax.
- Run the project's formatter, type-checker, linter, and tests. Exercise both the native path and compatibility path when both ship.
Read references/COMPATIBILITY.md whenever support is uncertain, the feature is newer than ES2023, or a proposal is involved.
Status Rules
- Use the frozen ECMAScript 2026 specification for ES2026 attribution and the living draft for already-integrated future features.
- Use TC39's finished-proposals table for Stage 4 publication-year mapping and its active tracker for current stages.
- Do not infer an edition from the year a browser shipped a feature.
Array.fromAsync, for example, shipped before its ES2026 publication. - Do not describe Stage 3 or 2.7 syntax as standard JavaScript. It can still be a sound project choice when a maintained toolchain implements the selected proposal revision.
- Do not emit withdrawn Records & Tuples syntax (
#{}/#[]).
What ships with it
11 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
- references/CHEATSHEET.md 13 KB
- references/COMPATIBILITY.md 10 KB
- references/CONCURRENCY.md 7.7 KB
- references/ES2016-ES2017.md 5.0 KB
- references/ES2018-ES2019.md 8.7 KB
- references/ES2022-ES2023.md 8.5 KB
- references/ES2024.md 7.5 KB
- references/ES2025.md 11 KB
- references/ES2026.md 7.7 KB
- references/PROMISES.md 7.0 KB
- references/UPCOMING.md 9.9 KB
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.
- 4d ago First seen · 182 lines · 111 tokens per session scan A 9ef7c2398ee4
modern-javascript is a skill published in the GitHub repository ccheney/robust-skills (57 stars, last pushed 7d ago), licensed MIT. It adds 111 tokens to every session and 2,551 once invoked, about $0.0006 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 2026-08-30.
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