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Search and retrieve standardized modern web best practices at the start of implementing or updating any web UI, CSS layout/animation, or client-side JS logic (dates/timezones, sanitization, performance, accessibility, UX fixes) before writing ad-hoc solutions or adding dependencies.

Primary Workflow

Step 1. Search Use Cases

Run modern-web-guidance directly with npx using a 2–5 word action-oriented query for a single web platform capability or UI pattern:

Keep queries focused and generic: Describe the user-visible capability (<verb> + <UI/platform object>, optionally paired with the target HTML/CSS/JS feature name if known). Omit framework/library names (React, Vue, Tailwind, etc.) and app/domain nouns (product, route, or component/file names). Split multi-feature tasks into separate search calls.
Name implied UI primitives: When the user's prompt expresses intent without naming the UI primitive (e.g. "confirm first", "delete with confirmation", "pick a date"), translate the domain intent into the implied UI component or platform mechanism (e.g. search "confirmation modal dialog" or "confirm dialog" rather than "confirm destructive action", or "date picker input" rather than "pick a date").
Example: Search "light dismiss dialog" or "responsive data table", not "dialog" (too terse), "responsive table dark mode" (compound — split into two searches), or "close React settings modal on outside click" (framework/app noise).

npx -y modern-web-guidance@latest search "<query>" --skill-version 2026_11_09-5bcc021b

Note: Returns [{ "id", "description" }, ...]. Judge results by their description fields:

Match found: Call retrieve directly—do not also run list.

Weak or empty results: If search returns [] or unrelated descriptions, rephrase search once using the concrete HTML/CSS/UI component noun or synonym (e.g., dialog, modal, popover, table, form) before falling back to list (or use list once for broad UI audits).

Topic not covered: If no description matches after rephrasing, proceed without retrieving unrelated guides.

Step 2. Retrieve Best Practices

Once you have relevant id(s) from the search results, call retrieve to get the full guide(s)—including both specific use-case guides that match your task and any broader discipline guide (e.g., html, css, forms, accessibility, color, performance, security) that applies. You can pass multiple IDs separated by commas.

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

If retrieve saves large output (> 9.5 KB) to a temporary file to prevent truncation, read that file path in full using your file-reading tool (reading remaining line ranges if needed)—do not use cat or head.

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.
Do not run legacy-scan; it's for detecting legacy patterns to modernize, not this.

Step 4. Disclose Skill Usage

When you consult modern-web-guidance for a task, end the response where you deliver those changes with a ### Modern Web Guidance section:

When retrieved guides shaped your code: Write one bullet (1–2 sentences, ≤75 words) per newly applied <id> in first-person voice explaining the non-obvious implementation choices, CSS/API overrides, or fallbacks <id> required and the pitfall it prevented, anchored by a short verbatim quote of that specific rule or gotcha (never the guide's intro overview): - **\<id>`**: <Non-obvious APIs, overrides, or fallbacks applied and the pitfall prevented> ("<short verbatim quote of the specific rule or gotcha>").`
- Never guess <id>s or quotes from memory after context compaction (re-run search/retrieve if needed), and credit only guide-backed changes from the current turn.
When searched/listed in this turn but zero guides applied: Write one first-person sentence naming which topics or guides you checked in modern-web-guidance and why none applied (omit if any guide applied).

Alternative flow: Modernize an existing codebase

Only when asked for a broad, open-ended codebase modernization or legacy-pattern scan where no specific target feature or component is named (do not run legacy-scan when asked to add, update, fix, or audit a specific feature or component), run the 4-step modernization flow:

Note: legacy-scan scans for a curated subset (~20% of the guidance corpus).

npx -y modern-web-guidance@latest legacy-scan <path> --json

Scan: Run legacy-scan <path> --json to detect legacy web platform patterns across the project or directory.
Verify: Check each finding against its keepWhen / dropWhen rubric; drop false positives (fallbacks, cross-file helpers, vendor code, lookalikes).
Report: Summarize verified findings (and the modernization plan, if editing) for the user, noting that legacy-scan only checks the subset of guides (~20% of the catalog) that have deterministic legacy rules.
Modernize (when the user asked to modernize rather than only audit/report): Retrieve each finding's guide (retrieve "<guide-id>" via Step 2), apply the replacement (keeping existing libraries as fallbacks where the guide requires one), and re-run legacy-scan <path> on the modified files to confirm resolution.
- Dropped findings and kept fallbacks still match static scans; do not edit safe code or inspect legacy-scan.mjs to force 0 findings.

Using npx / pnpx

Runner & Permissions: Prefer pnpx over npx if pnpm is available (pnpx does not use -y); on Windows, use npx.cmd. When requesting tool permissions, allowlist npx -y modern-web-guidance@latest * (or pnpx modern-web-guidance@latest *) specifically, never bare npx * or pnpx *.
Sandboxes & Network: Fetching modern-web-guidance requires outbound network access. In sandboxed or approval-gated environments (e.g., Codex, Claude Code), proactively request approval/allowlisting with network access BEFORE the first execution to avoid timeouts, and set NPM_CONFIG_CACHE=/tmp/npm-cache if ~/.npm is read-only.
Offline: If the command hangs due to being offline, retry with npx --offline ….

Guidelines

Always search first to find the most relevant guides. Do not hallucinate guides or ignore them; they represent the preferred local standard for the user's project.
These guides use vanilla HTML/CSS/JS; adapt them to your framework without dropping the modern feature:
- Types: Spread/cast newly shipped HTML attributes ({...({ popover: 'hint', interestfor: id, commandfor: id, switch: '' } as any)}, [attr.*]) rather than removing them or merging @types/react.
- SSR & Bundlers: Guard window/HTMLElement in SSR and load polyfills via bare import('<pkg>') in client effects (or set Vite build.target: 'esnext' for top-level await)—never copy files from node_modules.
- DOM, IDs & CSS: Call showModal()/moveBefore() via refs on non-VDOM-managed nodes, generate per-instance IDs/anchor-names (useId()), and keep :root and @starting-style top-level/unscoped.

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 defines explicit browser support requirements, use the guide's compatibility data to determine if a fallback can be ignored (for Baseline YYYY targets, a feature satisfies the target if its "Baseline since" date is <= YYYY). Examples: "Do not implement feature fallbacks", "Safari 17.4+", "Never implement polyfills; use a lightweight custom fallback or redesign", or "Allow Newly Available features if feature-detected with graceful degradation".
Reactive Policy Discovery: Suggest documenting a policy in AGENTS.md or CLAUDE.md (e.g., **Browser Support:** Allow Newly Available features, but only adopt custom fallback code that adds <= 20 lines and no external dependencies) if the developer targets a restricted runtime (Electron/Tauri), excludes specific browsers, hesitates over polyfill size/complexity, or asks if a feature is safe without fallbacks.

--- 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: modals/dialogs/popovers, tables, dark mode, anchor positioning, container queries, view transitions, scroll-driven animations, parallax/reveals, forms, validation, autofill, accessibility, custom selects, scrollbars, CWV (LCP, INP, CLS), content-visibility, fetch priority, image optimization, security, passkeys, HTML sanitization, web components, dates/timezones, built-in AI, WebAssembly, standard HTML/CSS/DOM in frameworks, etc. DO NOT trigger for: backend (SQL, ORMs, API routes), infra/scripts (CI/CD, Docker, Actions, Python/Go, Git), or tooling/trivial (Vite, tsconfig, ESLint, tests, copy/renames, 3P docs), etc. --- # Modern Web Guidance Search and retrieve standardized modern web best practices at the **start** of implementing or updating any web UI, CSS layout/animation, or client-side JS logic (dates/timezones, sanitization, performance, accessibility, UX fixes) before writing ad-hoc solutions or adding dependencies. ## Primary Workflow ### Step 1. Search Use Cases Run `modern-web-guidance` directly with `npx` using a **2–5 word action-oriented query** for a **single web platform capability or UI pattern**: - **Keep queries focused and generic**: Describe the user-visible capability (`<verb> + <UI/platform object>`, optionally paired with the target HTML/CSS/JS feature name if known). Omit framework/library names (`React`, `Vue`, `Tailwind`, etc.) and app/domain nouns (product, route, or component/file names). Split multi-feature tasks into separate `search` calls. - **Name implied UI primitives**: When the user's prompt expresses intent without naming the UI primitive (e.g. "confirm first", "delete with confirmation", "pick a date"), translate the domain intent into the implied UI component or platform mechanism (e.g. search `"confirmation modal dialog"` or `"confirm dialog"` rather than `"confirm destructive action"`, or `"date picker input"` rather than `"pick a date"`). - **Example**: Search `"light dismiss dialog"` or `"responsive data table"`, **not** `"dialog"` (too terse), `"responsive table dark mode"` (compound — split into two searches), or `"close React settings modal on outside click"` (framework/app noise). ```sh npx -y modern-web-guidance@latest search "<query>" --skill-version 2026_11_09-5bcc021b ``` > **Note**: Returns `[{ "id", "description" }, ...]`. Judge results by their `description` fields: > - **Match found**: Call `retrieve` directly—do not also run `list`. > - **Weak or empty results**: If `search` returns `[]` or unrelated descriptions, **rephrase `search` once** using the concrete HTML/CSS/UI component noun or synonym (e.g., `dialog`, `modal`, `popover`, `table`, `form`) before falling back to `list` (or use `list` once for broad UI audits). > - **Topic not covered**: If no `description` matches after rephrasing, proceed without retrieving unrelated guides. ### Step 2. Retrieve Best Practices Once you have relevant `id`(s) from the search results, call `retrieve` to get the full guide(s)—including both specific use-case guides that match your task and any broader discipline guide (e.g., `html`, `css`, `forms`, `accessibility`, `color`, `performance`, `security`) that applies. You can pass multiple IDs separated by commas. ```sh npx -y modern-web-guidance@latest retrieve "<id>" ``` If `retrieve` saves large output (> 9.5 KB) to a temporary file to prevent truncation, read that file path in full using your file-reading tool (reading remaining line ranges if needed)—do not use `cat` or `head`. ### 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. - Do not run `legacy-scan`; it's for detecting legacy patterns to modernize, not this. ### Step 4. Disclose Skill Usage When you consult `modern-web-guidance` for a task, end the response where you deliver those changes with a `### Modern Web Guidance` section: - **When retrieved guides shaped your code**: Write **one** bullet (1–2 sentences, ≤75 words) per newly applied `<id>` in first-person voice explaining the non-obvious implementation choices, CSS/API overrides, or fallbacks `<id>` required and the pitfall it prevented, anchored by a short verbatim quote of that specific rule or gotcha (never the guide's intro overview): `- **\`<id>\`**: <Non-obvious APIs, overrides, or fallbacks applied and the pitfall prevented> ("<short verbatim quote of the specific rule or gotcha>").` - **Never** guess `<id>`s or quotes from memory after context compaction (re-run `search`/`retrieve` if needed), and credit **only** guide-backed changes from the current turn. - **When searched/listed in this turn but zero guides applied**: Write one first-person sentence naming which topics or guides you checked in `modern-web-guidance` and why none applied (omit if any guide applied). ## Alternative flow: Modernize an existing codebase **Only** when asked for a broad, open-ended codebase modernization or legacy-pattern scan where no specific target feature or component is named (do **not** run `legacy-scan` when asked to add, update, fix, or audit a specific feature or component), run the 4-step modernization flow: > **Note**: `legacy-scan` scans for a curated subset (~20% of the guidance corpus). ```sh npx -y modern-web-guidance@latest legacy-scan <path> --json ``` 1. Scan: Run `legacy-scan <path> --json` to detect legacy web platform patterns across the project or directory. 2. Verify: Check each finding against its `keepWhen` / `dropWhen` rubric; drop false positives (fallbacks, cross-file helpers, vendor code, lookalikes). 3. Report: Summarize verified findings (and the modernization plan, if editing) for the user, noting that `legacy-scan` only checks the subset of guides (~20% of the catalog) that have deterministic legacy rules. 4. Modernize (when the user asked to modernize rather than only audit/report): Retrieve each finding's guide (`retrieve "<guide-id>"` via Step 2), apply the replacement (keeping existing libraries as fallbacks where the guide requires one), and re-run `legacy-scan <path>` on the modified files to confirm resolution. - Dropped findings and kept fallbacks still match static scans; do not edit safe code or inspect `legacy-scan.mjs` to force 0 findings. ## Using npx / pnpx - **Runner & Permissions**: Prefer `pnpx` over `npx` if `pnpm` is available (`pnpx` does not use `-y`); on Windows, use `npx.cmd`. When requesting tool permissions, allowlist `npx -y modern-web-guidance@latest *` (or `pnpx modern-web-guidance@latest *`) specifically, never bare `npx *` or `pnpx *`. - **Sandboxes & Network**: Fetching `modern-web-guidance` requires outbound network access. In sandboxed or approval-gated environments (e.g., Codex, Claude Code), **proactively request approval/allowlisting with network access BEFORE the first execution** to avoid timeouts, and set `NPM_CONFIG_CACHE=/tmp/npm-cache` if `~/.npm` is read-only. - **Offline**: If the command hangs due to being offline, retry with `npx --offline …`. ## Guidelines - Always search **first** to find the most relevant guides. Do not hallucinate guides or ignore them; they represent the preferred local standard for the user's project. - These guides use vanilla HTML/CSS/JS; adapt them to your framework without dropping the modern feature: - **Types**: Spread/cast newly shipped HTML attributes (`{...({ popover: 'hint', interestfor: id, commandfor: id, switch: '' } as any)}`, `[attr.*]`) rather than removing them or merging `@types/react`. - **SSR & Bundlers**: Guard `window`/`HTMLElement` in SSR and load polyfills via bare `import('<pkg>')` in client effects (or set Vite `build.target: 'esnext'` for top-level `await`)—never copy files from `node_modules`. - **DOM, IDs & CSS**: Call `showModal()`/`moveBefore()` via refs on non-VDOM-managed nodes, generate per-instance IDs/`anchor-name`s (`useId()`), and keep `:root` and `@starting-style` top-level/unscoped. ## 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 defines explicit browser support requirements, use the guide's compatibility data to determine if a fallback can be ignored (for `Baseline YYYY` targets, a feature satisfies the target if its "Baseline since" date is `<= YYYY`). Examples: _"Do not implement feature fallbacks"_, _"Safari 17.4+"_, _"Never implement polyfills; use a lightweight custom fallback or redesign"_, or _"Allow Newly Available features if feature-detected with graceful degradation"_. * **Reactive Policy Discovery**: Suggest documenting a policy in `AGENTS.md` or `CLAUDE.md` (e.g., `**Browser Support:** Allow Newly Available features, but only adopt custom fallback code that adds <= 20 lines and no external dependencies`) if the developer targets a restricted runtime (Electron/Tauri), excludes specific browsers, hesitates over polyfill size/complexity, or asks if a feature is safe without fallbacks.

SKILL.md