/modern-web-guidance

name: modern-web-guidance
description: |
  Search tool for modern web development best practices. MANDATORY: Execute FIRST for all HTML/CSS and clientside JS tasks. Do NOT skip — web APIs evolve rapidly and training weights contain obsolete patterns.

  Trigger immediately for:
  - UI/Layout: Modals, dialogs, popovers, Glassmorphism/backdrop-filters, anchor positioning, container queries, `:has()`, `:user-valid`.
  - Scroll/Motion: View Transitions, Scroll-driven animations, scroll parallax/reveals.
  - Performance: CWV (LCP, INP), content-visibility, Fetch Priority, image optimization.
  - System/APIs: Local filesystem access, WebUSB, WebSockets sync, WebAssembly widgets.
  - Frameworks: Adapting layout/styles in React, Vue, Angular.
  - General Frontend: Forms, autofill, advanced inputs, custom scrollbars, modern component states, etc.

  DO NOT trigger for:
  - Backend: Database SQL, ORMs, Express API routes.
  - Pipelines: CI/CD deployment, Docker, Actions.
  - Generic: Local scripts (Python/Go tools), ESLint, Git.

Modern Web Guidance

A skill to search for specific web development use cases and retrieve their corresponding best practice guides.

When to use

Must use this skill:

• At the **start** of implementing any web feature.
• Before creating a new component, to check if a standardized pattern already exists.
• To avoid implementing ad-hoc solutions or loading large dependencies unnecessarily.

Usage Instructions

Step 1. Search Use Cases

Search with an action-oriented query summarizing what you want to achieve using the `search` command. Run `modern-web-guidance` directly with `npx`.

npx -y modern-web-guidance@latest search "<query>" --skill-version 2026_09_04-7de96777

**Example Output**:

[
  {
    "id": "optimize-image-priority",
    "description": "Optimize the loading priority of Largest Contentful Paint (LCP) candidate images.",
    "category": "performance",
    "featuresUsed": [ "Fetch priority" ],
    "tokenCount": 985,
    "similarity": 0.7289
  },
  {
    "id": "defer-rendering-heavy-content",
    "description": "Reduce rendering times in content-heavy web pages by deferring rendering for offscreen content.",
    "category": "performance",
    "featuresUsed": [ "content-visibility", "hidden=\"until-found\"" ],
    "tokenCount": 1250,
    "similarity": 0.6961
  }
]

> **Note**: If search results are vague, return no matches, or show low similarity scores, run the `list` command to browse all guides: > ```sh > npx -y modern-web-guidance@latest list > ```

---

Step 2. Retrieve Best Practices

Once you have a relevant `id` from the search results, call this script using the `retrieve` command to get the full guide. You can pass multiple IDs separated by commas.

npx -y modern-web-guidance@latest retrieve "<id>"

If the output is truncated, you must repeat the command but redirect to a file and read that file.

**Example Output**: `The markdown content of the guide describing implementation steps...`

---

Step 3. Verify Guidance Compliance

When generating or modifying code, cross-check the implementation against the retrieved guide before concluding:

• **Applicable Guidance & Fallbacks**: Ensure the relevant modern patterns and necessary fallback strategies from the guide are correctly applied, without forcing unrequested features.
• **Task Fulfillment**: Confirm that the implementation fully satisfies the user's request.

Using npx / pnpx

• Prefer `pnpx` over `npx` if `pnpm` is available (note: `pnpx` does not use the `-y` flag).
• When requesting tool permissions, allowlist `npx -y modern-web-guidance@latest *` specifically (or `pnpx modern-web-guidance@latest *`), never bare `npx *` or `pnpx *`.
• IMPORTANT: on Windows, using `npx` may fail. Use `npx.cmd ...` instead.
• Fetching and running `modern-web-guidance` requires outbound network access. If running in a sandboxed, permission-gated, or approval-based environment (e.g., Codex, Claude Code), **proactively request approval/allowlisting for the command with network access BEFORE executing it the first time**, avoiding sandbox network timeouts.
• In sandboxed environments where `~/.npm` is read-only or restricted, set `NPM_CONFIG_CACHE=/tmp/npm-cache`.
• If the command hangs due to being offline, try running again in offline mode: `npx --offline …`.
• The `--skill-version` flag is used to determine if this SKILL.md is out of date. If it is, a warning message is logged to stderr.

Guidelines

• Always search **first** to find the most relevant guides.
• These guides are usually framework-agnostic; adapt them correctly to your setup.
• Do not hallucinate guides or ignore them; they represent the preferred local standard for the user's project.

Interpreting Browser Support & Fallbacks

• **Default Behavior**: All guides assume **Baseline Widely available** features are safe to use without fallbacks. For features that are not Baseline widely available, you **MUST** follow the fallback recommendations in the guide, unless the user has specified a custom browser support policy.
• **Custom Policies**: If the user has already defined explicit browser support requirements, use the browser compatibility data in the guide to determine if a fallback can be safely ignored.
• For Baseline YYYY targets, a feature satisfies this target if its "Baseline since" date is <= YYYY.
• **Policy Examples**:
• _"Do not implement feature fallbacks."_ (for exploratory prototypes of the cutting-edge web)
• _"Safari 17.4+"_ (for internal tools targeting macOS or Tauri-based desktop apps)
• _"Never recommend or implement polyfills; if a Baseline Newly Available feature is required for core functionality, provide a lightweight custom fallback or redesign the approach."_ (to minimize bundle size and avoid technical debt)
• _"Assume a modern execution environment where Baseline Newly Available features can be used natively, provided they are strictly feat