33 JavaScript Concepts is a learning guide that explains core JavaScript ideas through practical examples and selected resources. It helps developers understand topics such as primitive values, objects, coercion, equality, scope, closures, and the call stack. The catalogue add-ons provide skills related to studying or working with the guide.
Borrowing it
Nothing to install: this file belongs to leonardomso/33-js-concepts. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/leonardomso/33-js-concepts/master/.claude/skills/seo-review/SKILL.mdgit clone --depth 1 https://github.com/leonardomso/33-js-conceptsWrote 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/leonardomso/33-js-concepts/seo-review)<a href="https://agentmods.dev/skills/leonardomso/33-js-concepts/seo-review"><img src="https://agentmods.dev/badge/skills/leonardomso/33-js-concepts/seo-review/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/skills/leonardomso/33-js-concepts/seo-review"><img src="https://agentmods.dev/badge/skills/leonardomso/33-js-concepts/seo-review.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- Socket pass
- Snyk pass
- NVIDIA SkillSpector pass
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 | $0.00025 | $0.08270 |
| Opus 5 | $0.00013 | $0.04135 |
| Sonnet 5 | $0.00005 | $0.01654 |
| Haiku 4.5 | $0.00003 | $0.00827 |
Grade A, and why
seo-review 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 13d 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.
Copies of this mod
1 near-identical copy found in the catalogue:
- seo-review — 100% identical, 2 lines differ
How it starts
The opening of the file, as written. The whole thing — 952 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Skill: SEO Audit for Concept Pages
Use this skill to perform a focused SEO audit on concept documentation pages for the 33 JavaScript Concepts project. The goal is to maximize search visibility for JavaScript developers.
When to Use
- Before publishing a new concept page
- When optimizing underperforming pages
- Periodic content audits
- After major content updates
- When targeting new keywords
Goal
Each concept page should rank for searches like:
- "what is [concept] in JavaScript"
- "how does [concept] work in JavaScript"
- "[concept] JavaScript explained"
- "[concept] JavaScript tutorial"
- "[concept] JavaScript example"
SEO Audit Methodology
Follow these five steps for a complete SEO audit.
Step 1: Identify Target Keywords
Before auditing, identify the keyword cluster for the concept.
Keyword Cluster Template
| Type | Pattern | Example (Closures) |
|---|---|---|
| Primary | [concept] JavaScript | closures JavaScript |
| What is | what is [concept] in JavaScript | what is a closure in JavaScript |
| How does | how does [concept] work | how do closures work |
| How to | how to use/create [concept] | how to use closures |
| Why | why use [concept] | why use closures JavaScript |
| Examples | [concept] examples | closure examples JavaScript |
| vs | [concept] vs [related] | closures vs scope |
| Interview | [concept] interview questions | closure interview questions |
Step 2: On-Page SEO Audit
Check all on-page SEO elements systematically.
Step 3: Featured Snippet Optimization
Verify content is structured to win featured snippets.
Step 4: Internal Linking Audit
Check the internal link structure.
Step 5: Generate Report
Document findings using the report template.
Keyword Clusters by Concept
Use these pre-built keyword clusters for each concept.
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.
- 13d ago First seen · 952 lines · 25 tokens per session scan A 78d1f882ce81
seo-review is a skill published in the GitHub repository leonardomso/33-js-concepts (66,525 stars, last pushed yesterday), licensed MIT. It adds 25 tokens to every session and 8,270 once invoked, about $0.0001 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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