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Modern Web Guidance

JetBrainsOfficialCreated by Google ChromeDistributed by JetBrains

  • Skill
  • Tool integration
  • Software development
  • Apache-2.0
  • Low risk
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From the author

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.
— the description by Google Chrome

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

This skill provides a structured way to access up-to-date web development patterns, ensuring that implementations follow modern standards rather than relying on potentially outdated training data. It covers a wide range of frontend topics including UI components, performance optimization, browser APIs, and form handling. By integrating this tool, developers can search for specific use cases and retrieve detailed, framework-agnostic guides that include browser support and fallback recommendations.

What it does

  • Searches for standardized web development patterns and best practices.
  • Retrieves detailed implementation guides for specific frontend use cases.
  • Provides guidance on browser compatibility and necessary fallbacks.
  • Helps avoid ad-hoc solutions and unnecessary dependency bloat.
  • Supports modern web features like container queries, view transitions, and performance APIs.

When to use it

  • At the beginning of any frontend feature implementation.
  • Before creating new components to check for existing standardized patterns.
  • When evaluating the browser support requirements for modern web features.
  • When needing to implement performance optimizations like LCP or content-visibility.

Advantages

  • Ensures use of current, recommended web development practices.
  • Reduces technical debt by discouraging ad-hoc implementations.
  • Provides clear guidance on handling browser compatibility and fallbacks.
  • Promotes the use of native browser capabilities over heavy external dependencies.

Usage examples

“I need to implement a modal using modern web standards. What is the best approach?”
The agent searches for modal-related guides and retrieves the recommended implementation pattern, including any necessary browser fallbacks.
“How can I optimize the loading priority of my LCP images?”
The agent searches for image optimization guides and retrieves the specific instructions for using fetch priority to improve performance.

Install

  1. Download the skill as a ZIP:

    https://mp-staging.autogineer.com/agent-skills/jetbrains/modern-web-guidance/download

  2. Unzip it into the cross-client skills folder of your project:

    mkdir -p .agents/skills && unzip modern-web-guidance.zip -d .agents/skills

Documentation by Google Chrome

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_05_16-c5e7870

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:

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>"

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

Using npx

  • IMPORTANT: on Windows, using npx may fail. Use npx.cmd ... instead.

  • Network access is required for fetching npm packages needed by the task.

  • If the npx -y modern-web-guidance… command hangs, you may be 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 feature-detected and degrade gracefully." (for progressive enhancement strategies)

  • Reactive Policy Discovery: Watch for environmental cues to suggest documenting a policy in CLAUDE.md or AGENTS.md. Suggest this if the developer:

    • Mentions building for a restricted runtime (e.g., Electron or Tauri).

    • Explicitly excludes specific targets (e.g., "we don't support Desktop Chrome").

    • Expresses hesitation about polyfill complexity, bundle size, or performance cost.

    • Questions if a feature is safe to use without fallbacks.

    No defined policy format. This is an example: **Browser Support:** Allow Newly Available features, but only adopt custom fallback code that adds <= 20 lines and does not require external dependencies.

Files

guides/forms/select-menu-interaction.md

Select Menu Interaction

The Problem

For mandatory dropdowns (e.g., "Choose a Country"), standard validation flags the field as invalid immediately if the default option has an empty value. This can create visual noise. We want to show the error only if the user opens the menu and closes it without choosing an option, or attempts to submit the form.

The Solution

The :user-invalid pseudo-class works seamlessly with <select> elements. It respects the user's interaction flow: simply loading the page or focusing/blurring without making a change doesn't count as an interaction, so the field stays neutral until they actively attempt a selection.

Implementation Strategy

  1. HTML Constraint: Use a <select> with required. The first option should have value="" and ideally be disabled/hidden to force a valid choice.

  2. Visual Feedback: Use :user-invalid to style the select box border.

  3. Timing: The browser considers the field "interacted" if the user changes the value (even back to the default invalid state) before they blur the control, or upon form submission.

Implementation Guide

1. HTML Structure

The "placeholder" option is key here.

<form>
  <div class="field">
    <label for="country">Country</label>
    <select
      id="country"
      name="country"
      required
      aria-errormessage="country-error"
    >
      <option value="" disabled selected>Select a country...</option>
      <option value="us">United States</option>
      <option value="ca">Canada</option>
      <option value="uk">United Kingdom</option>
    </select>
    <div id="country-error" class="error-msg">
      Please select a country.
    </div>
  </div>
</form>
2. CSS
.error-msg {
  display: none;
  color: #d93025;
  font-size: 0.875rem;
  margin-top: 0.25rem;
}

/*
  Only show error after the user visits the select menu.
*/
select:user-invalid {
  border-color: #d93025;
  background-color: #fce8e6;
}

select:user-invalid + .error-msg {
  display: block;
}

select:user-valid {
  border-color: #188038;
}

Fallbacking & Browser Support

The :user-invalid pseudo-class is widely supported (Baseline 2023), but if you need to support older browsers, you must ensure consistency of the implementation.

Fallbacks & browser support for :user-valid and :user-invalid

Baseline status for :user-valid and :user-invalid: Widely available. It's been Baseline since 2023-11-02. Supported by: Chrome 119 (Oct 2023), Edge 119 (Nov 2023), Firefox 88 (Apr 2021), and Safari 16.5 (May 2023).

CSS for Fallback
input:user-invalid,
input.user-invalid-fallback {
  border-color: #d93025;
  background-color: #fce8e6;
}

input:user-invalid + .error-msg,
input.user-invalid-fallback + .error-msg {
  display: block;
}
JavaScript Fallback

Use a reusable utility that tracks interaction state using a WeakMap. This avoids polluting the DOM with "dirty" classes or data attributes.

const UserInvalidFallback = (() => {
  const dirtyState = new WeakMap();

  const updateState = (input) => {
    const isValid = input.checkValidity();

    // Update both visual and ARIA state
    input.classList.toggle('user-invalid-fallback', !isValid);
    input.classList.toggle('user-valid-fallback', isValid);

    if (!isValid) {
      input.setAttribute('aria-invalid', 'true');
    } else {
      input.removeAttribute('aria-invalid');
    }
  };

  const handleEvent = (event) => {
    const input = event.target;

    if (event.type === 'reset') {
      const controls = input.elements || [];
      for (const control of controls) {
        dirtyState.delete(control);
        control.classList.remove('user-invalid-fallback');
        control.classList.remove('user-valid-fallback');
        control.removeAttribute('aria-invalid');
      }
      return;
    }

    if (!input.checkValidity) return;

    if (event.type === 'input' || event.type === 'change') {
      const state = dirtyState.get(input) || { hasInteracted: false, hasBlurred: false };
      state.hasInteracted = true;
      dirtyState.set(input, state);
      if (state.hasBlurred) {
        updateState(input);
      }
    } else if (event.type === 'blur') {
      const state = dirtyState.get(input) || { hasInteracted: false, hasBlurred: false };
      state.hasBlurred = true;
      dirtyState.set(input, state);
      if (state.hasInteracted) {
        updateState(input);
      }
    }
  };

  const init = (root = document) => {
    if (CSS.supports('selector(:user-invalid)')) return;

    root.addEventListener('blur', handleEvent, true); // Capture phase
    root.addEventListener('input', handleEvent);
    root.addEventListener('change', handleEvent);
    root.addEventListener('reset', handleEvent, true); // Capture resets
  };

  return { init };
})();

// Initialize for a specific form
const form = document.querySelector('#demo-form');
UserInvalidFallback.init(form);

Other Considerations

  1. Mobile behavior: On mobile devices, "blur" might happen differently depending on the OS picker. Testing on actual devices is recommended.

  2. Accessibility: Native :user-invalid does not automatically sync with ARIA attributes. Add the following JavaScript to keep aria-invalid in sync with the visual state:

// Sync aria-invalid with the CSS :user-invalid state
const syncAria = (el) => {
  el.setAttribute?.('aria-invalid', el.matches(':user-invalid') ? 'true' : 'false');
};

// Update on blur (to show error) and input (to clear it)
document.addEventListener('blur', (e) => syncAria(e.target), true);
document.addEventListener('input', (e) => {
  if (e.target.hasAttribute('aria-invalid')) syncAria(e.target);
});

Requirements and compatibility

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

Needs: Needs Node.js

Security

What our scanner noticed· Low risk

  • Instructions that use the network

A static scan is not a guarantee. Skills are third-party content: review a skill before you let an agent use it.

Attribution and licence

Created by
Google Chrome
Publisher
JetBrains (Official)
Distributed by
JetBrains
Source
JetBrains/skills · modern-web-guidance · commit 3f53782
Licence
Apache License 2.0 (redistribution allowed)
  • ATTRIBUTION.md (written by AutoGineer)
Synced

AutoGineer is not affiliated with or endorsed by Google Chrome or JetBrains.

Download ZIP

The ZIP holds the skill’s files, its licence files and an ATTRIBUTION.md. Download modern-web-guidance.zip