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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web development patterns, ensuring that implementations follow modern standards rather than relying on potentially outdated training data.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://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/css/highlight-text-ranges.md

The CSS Custom Highlight API lets you style arbitrary text ranges on a page without modifying the DOM structure. This enables search-result highlighting, syntax coloring, collaborative editing cursors, or spelling and grammar error markers without wrapping text in extra elements or relying on innerHTML manipulation.

Core implementation

To highlight text ranges, you must collect the target text nodes, create Range and Highlight objects, register them in the HighlightRegistry, and then style them with the ::highlight() pseudo-element.

1. Collect text nodes and create ranges

Use a TreeWalker to collect all text nodes in the target element, then create Range objects pointing at the character offsets you want to highlight.

const article = document.querySelector("article");

// MANDATORY: Use TreeWalker to collect text nodes — do not manipulate innerHTML.
const treeWalker = document.createTreeWalker(article, NodeFilter.SHOW_TEXT);
const allTextNodes = [];
let currentNode = treeWalker.nextNode();
while (currentNode) {
  allTextNodes.push(currentNode);
  currentNode = treeWalker.nextNode();
}

// MANDATORY: Set range start/end on text nodes, not element nodes.
const range = new Range();
range.setStart(textNode, matchStartIndex);
range.setEnd(textNode, matchEndIndex);

Cache the text-node list and only rebuild it when the DOM content actually changes, since walking the tree is expensive.

2. Create a Highlight from the ranges

Group one or more Range objects into a Highlight. Multiple ranges that share the same style belong in a single highlight.

const searchHighlight = new Highlight(...matchingRanges);
3. Register the highlight in the registry

Register each Highlight under a custom name using CSS.highlights, which is a Map-like HighlightRegistry.

// MANDATORY: Clear previous highlights before registering new ones
// to avoid stale ranges persisting on the page.
CSS.highlights.clear();

CSS.highlights.set("search-results", searchHighlight);

When multiple highlights overlap, use the priority property to control stacking order. Higher priority highlights paint on top.

const primary = new Highlight(...primaryRanges);
primary.priority = 1;

const secondary = new Highlight(...secondaryRanges);
secondary.priority = 0; // painted first (behind primary)

CSS.highlights.set("primary", primary);
CSS.highlights.set("secondary", secondary);
4. Style with ::highlight()

Use the ::highlight() pseudo-element in CSS to style each registered highlight by name.

::highlight(search-results) {
  background-color: #ffdd00;
  color: black;
}

Only a limited set of CSS properties work inside ::highlight(): color, background-color, text-decoration and its longhands, text-shadow, -webkit-text-stroke-color, -webkit-text-fill-color, and -webkit-text-stroke-width. Properties like background-image, font-size, or padding are ignored.

Accessibility

AVOID: using custom highlights as a replacement for semantic HTML.

Custom highlights are purely presentational and are not exposed to the accessibility tree. If the highlighted text is semantically relevant to the document (e.g., a user-selected passage), use <mark> instead. Reserve custom highlights for transient, visual-only effects like search results or syntax coloring.

Highlights should not rely solely on color to convey meaning. If a highlight indicates an error, pair it with another visual indicator such as text-decoration: wavy underline or an adjacent text label. Ensure sufficient contrast between the highlight background and text color to meet WCAG 2.1 requirements (at least 4.5:1 for normal text).

Fallback strategies

Baseline status for Custom highlights: Newly available. It's been Baseline since 2026-03-24. Supported by: Chrome 105 (Sep 2022), Edge 105 (Sep 2022), Firefox 149 (Mar 2026), and Safari 17.2 (Dec 2023).

For browsers that do not support the CSS Custom Highlight API, you should provide a functional base experience where text is still legible, even without the visual highlight.

You can detect support before using the API:

if (CSS.highlights) {
  // CSS Custom Highlight API is supported.
} else {
  // Fallback: wrap matches in <mark> elements.
}

If the highlight is critical for the user experience, fall back to wrapping matched text in <mark> elements. This modifies the DOM, so take care to preserve event listeners and avoid breaking the document structure.

if (!CSS.highlights) {
  // Walk text nodes and wrap matches in <mark>, preserving structure.
  const walker = document.createTreeWalker(article, NodeFilter.SHOW_TEXT);
  const nodes = [];
  for (let n = walker.nextNode(); n; n = walker.nextNode()) nodes.push(n);

  const term = searchTerm.toLowerCase();
  for (const textNode of nodes) {
    const text = textNode.textContent;
    let pos = text.toLowerCase().indexOf(term);
    if (pos === -1) continue;

    const frag = document.createDocumentFragment();
    let last = 0;
    while (pos !== -1) {
      frag.append(text.slice(last, pos));
      const mark = document.createElement("mark");
      // textContent assignment avoids HTML injection.
      mark.textContent = text.slice(pos, pos + term.length);
      frag.append(mark);
      last = pos + term.length;
      pos = text.toLowerCase().indexOf(term, last);
    }
    frag.append(text.slice(last));
    textNode.replaceWith(frag);
  }
}

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