Vanilla Web (HTML/CSS/JS)

Baseline constraints (from the rule)

Use these as non-negotiables:

• "HTML/CSS/JS only (no framework)."
• "Keep JS modular (ESM), split responsibilities (SRP)."
• "Prefer small, focused functions and pure utilities; avoid global state."
• "Ship complete runnable files and minimal tests before marking done."

When to activate this skill

Activate when the user asks for:

• vanilla JS / plain HTML/CSS/JS / static page
• “no framework”, “no React/Vue/Angular”
• small UI components (modal, tabs, dropdown, form validation) built directly in the DOM
• refactors to remove framework dependencies or reduce JS complexity

Output expectations

1. Deliver complete runnable files (no missing imports/paths, no TODO placeholders).
2. Keep changes small, testable, and incremental.
3. Provide a short runbook: how to run/verify locally + what to check in DevTools.

Implementation workflow

1) Clarify only what blocks correctness

Ask up to 3 questions only if requirements are ambiguous in a way that changes implementation. Otherwise proceed with explicit assumptions.

2) Structure & responsibilities

• Prefer this split:

- index.html (semantic markup) - styles.css (or css/…) - js/main.js as an ESM entrypoint + js/modules/*.js for components/utilities

• SRP: each module does one thing (DOM wiring, state, rendering, API, utilities).
• Avoid global mutable state. If state is needed, encapsulate it in a module and expose minimal functions.

3) HTML guidelines

• Use semantic tags (header, main, nav, button, dialog where applicable).
• Accessibility baseline: keyboard navigation, focus states, ARIA only when needed (don’t ARIA-overuse).

4) CSS guidelines

• Prefer simple, predictable naming (BEM-like optional).
• Use CSS variables for theme primitives.
• Keep layout responsive by default (flex/grid + relative units).

5) JavaScript guidelines (ESM)

• Use type="module" and explicit imports/exports.
• Prefer pure utilities and small functions.
• Use event delegation for lists/dynamic UIs.
• Handle errors explicitly (network failures, missing DOM nodes, invalid inputs).

Verification checklist

Use the detailed checklist in:

• references/checklist.md

When finishing work, ensure:

• No console errors/warnings caused by the change
• All referenced assets resolve (paths/imports)
• Feature works with keyboard and without requiring a framework runtime

Progressive disclosure

Keep this SKILL.md lean; store deeper examples and checklists under references/. Do not paste large style guides into SKILL.md—link to repo examples instead.

Suggested companion scripts (optional)

• scripts/serve.sh for quick static serving (manual verification)

See:

• scripts/serve.sh