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/leonardomso/33-js-concepts/test-writernpx skills add leonardomso/33-js-concepts --skill test-writergit clone --depth 1 https://github.com/leonardomso/33-js-conceptsWhat 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 | $0.00026 | $0.05390 |
| Opus 5 | $0.00013 | $0.02695 |
| Sonnet 5 | $0.00005 | $0.01078 |
| Haiku 4.5 | $0.00003 | $0.00539 |
Grade A, and why
test-writer 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 yesterday.
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 — 941 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Skill: Test Writer for Concept Pages
Use this skill to generate comprehensive Vitest tests for all code examples in a concept documentation page. Tests verify that code examples in the documentation are accurate and work as described.
When to Use
- After writing a new concept page
- When adding new code examples to existing pages
- When updating existing code examples
- To verify documentation accuracy through automated tests
- Before publishing to ensure all examples work correctly
Test Writing Methodology
Follow these four phases to create comprehensive tests for a concept page.
Phase 1: Code Example Extraction
Scan the concept page for all code examples and categorize them:
| Category | Characteristics | Action |
|---|---|---|
| Testable | Has console.log with output comments, returns values |
Write tests |
| DOM-specific | Uses document, window, DOM APIs, event handlers |
Write DOM tests (separate file) |
| Error examples | Intentionally throws errors, demonstrates failures | Write tests with toThrow |
| Conceptual | ASCII diagrams, pseudo-code, incomplete snippets | Skip (document why) |
| Browser-only | Uses browser APIs not available in jsdom | Skip or mock |
Phase 2: Determine Test File Structure
tests/
├── fundamentals/ # Concepts 1-6
├── functions-execution/ # Concepts 7-8
├── web-platform/ # Concepts 9-10
├── object-oriented/ # Concepts 11-15
├── functional-programming/ # Concepts 16-19
├── async-javascript/ # Concepts 20-22
├── advanced-topics/ # Concepts 23-31
└── beyond/ # Extended concepts
└── {subcategory}/
File naming:
- Standard tests:
{concept-name}.test.js - DOM tests:
{concept-name}.dom.test.js
Phase 3: Convert Examples to Tests
For each testable code example:
- Identify the expected output (from
console.logcomments or documented behavior) - Convert to
expectassertions - Add source line reference in comments
- Group related tests in
describeblocks matching documentation sections
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.
- yesterday First seen · 941 lines · 26 tokens per session scan A 76dda6fa2dd6
test-writer is a skill published in the GitHub repository leonardomso/33-js-concepts (66,520 stars, last pushed 29d ago), licensed MIT. It adds 26 tokens to every session and 5,390 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.
Other skills, from other repositories
hidden-admin-auth
Configure the private route as a hidden admin utility. Moves credentials to env vars; operator updates .env using .envTemplate instructions. No credentials passed to the skill.
migrate-ci-github-to-gitlab
Replace GitHub Actions CI with GitLab CI/CD while preserving the same lint, typecheck, and Playwright E2E behavior and updating docs for gitlab.com settings.
rebrand
Use this immediately after cloning the boilerplate to convert it into a new project identity. Trigger whenever a developer provides a new site title/description and wants boilerplate branding removed from centralized metadata (PageMeta), docs, and shared public/private header branding.
api-first
Maintain the OpenAPI contract in docs, regenerate TypeScript types into src/generated/api, and wire client/server imports without hand-editing generated files.
migrate-api-to-graphql-client
Migrate the REST client path to a GraphQL client architecture with typed operations and incremental rollout.
migrate-api-to-tanstack-query
Migrate the current REST API usage to TanStack Query with server-state caching, invalidation, and progressive rollout.