Modern Web Guidance (Source)

This repo is the source repository for GoogleChrome/modern-web-guidance and includes the code and documentation for authoring, calibrating, and evaluating its contents.

Modern Web Guidance is a set of skills that embed web platform expertise, best practices, and browser compatibility data directly into your coding agents. It helps to steer your coding agents away from legacy patterns, and instead toward solutions that harness the power and capabilities of the modern web platform.

Note

This is a preview release of Modern Web Guidance. We're actively adding new content and we welcome contributions or feedback on GitHub.

See CONTRIBUTING.md for how we work on the project and orientation of the codebase. We're open to contributions to guidance, eval cases, eval infra and more. :)

Supported by the Google Chrome team, the Microsoft Edge team, and the web development community.

Quickstart

npx modern-web-guidance@latest install

This command runs an interactive wizard to install Modern Web Guidance. See Alternative Installation Methods below.

Try it out (without installing)

# Search for relevant guides
npx modern-web-guidance@latest search "animate a dialog modal backdrop"

# Retrieve a guide by ID
npx modern-web-guidance@latest retrieve "animate-to-from-top-layer"

Why?

Coding agents often default to older patterns because LLM training data contains vast amounts of legacy code. This often leads them to generate bloated JavaScript for tasks that now have native, high-performance web platform solutions.

Even if a model knows an API exists, it often lacks the density of real-world, modern implementation patterns required for production-ready code.

Modern Web Guidance bridges this gap. Our skill's CLI returns targeted, expert-curated guidelines directly into your agent's context window, focusing on:

Modern Browser APIs: Helping models correctly structure APIs they frequently misuse.
Performance & Accessibility: Preferring platform-level APIs that can be optimized by the browser and include built-in accessibility affordances.
Responsible Fallbacks: Guiding models to use sensible, lightweight fallbacks instead of heavy polyfills or legacy libraries.

What's Included?

We cover the past several years of the web platform's new features, all the way up to the cutting edge. The guides are designed to be token-efficient; we run evals enabling us to prune lowest-common-denominator content that models already know.

Core Disciplines

🎨 User Experience Smooth visual states (View Transitions, entry/exit animations, parallax scroll, CSS `scrollbar-color`).	📐 CSS Layout Modern layout systems (container queries, `subgrid`, modern color spaces like `oklch`, text-wrap tuning, and line-height trimming).	⚡ Performance Speed optimizations (instant preloading, Interaction to Next Paint (INP) diagnostics, and scheduling tasks via `scheduler.yield`).
📝 Forms & UI Native components (Anchor Positioning for tooltips, Popover API, dialogs, `:user-invalid` validation, and auto-sizing fields).	♿ Accessibility Important considerations (screen reader and keyboard operability, content navigation and discoverability).	🤖 Built-in AI Local client models (native translation, summarization, and language detection APIs).

View an example: the navigation-drawer guide.

The full list

104 modern web features

CSS & Layout (51 features)


::backdrop	Custom highlights	Scroll snap events
:has()	field-sizing	Scroll-driven animations
:not()	font-size-adjust	scroll-initial-target
:user-valid and :user-invalid	image-set()	scrollbar-color
@function	Individual transform properties	scrollbar-width
@starting-style	interpolate-size	scrollend
accent-color	light-dark()	scrollIntoView()
Active view transition	linear() easing	sibling-count() and sibling-index()
Anchor position container queries	Masks	text-box
Anchor positioning	overflow-clip-margin	text-wrap
calc-size()	overflow: clip	text-wrap: balance
color-scheme	overlay	text-wrap: pretty
Container queries	overscroll-behavior	transition-behavior
Container scroll-state queries	prefers-color-scheme media query	Trigonometric functions (CSS)
Container style queries	prefers-contrast media query	View transitions
content-visibility	prefers-reduced-motion media query	view-transition-class
Cross-document view transitions	Scroll snap	Web animations

HTML & DOM (20 features)


:autofill	Customizable <select>	Invoker commands
<details>	Email, telephone, and URL <input> types	moveBefore()
<dialog closedby>	Fetch priority	MutationObserver
<dialog>	hidden="until-found"	Mutually exclusive <details> elements
<link rel="expect">	HTML in canvas	Popover
<link rel="preload">	inert	popover="hint"
blocking="render"	Interest invokers

JavaScript & APIs (33 features)


AbortController and AbortSignal	Keyboard events	Resize observer
document.modelContext	Language detector	Scheduler API
enterkeyhint	LanguageModel	Speculation rules
Event timing	Lazy-loading images and iframes	Summarizer
Federated credential management	Long animation frames	SVG
Fetch	Navigation API	Temporal
fetchLater	Page visibility	Top-level await
Form-associated WebMCP attributes	Page visibility state	Translator
inputmode	Partitioned cookies	User agent client hints
Intersection observer	Permissions policy	Web authentication
Intl.DurationFormat	Registered custom properties	Web authentication signal methods

132 real-world developer use cases

accessibility

accessible-error-announcement: Synchronize programmatic accessibility states (like aria-invalid) with the visual :user-invalid state to ensure screen reader users receive error feedback only after interaction, mirroring the visual experience.

built-in-ai

language-detection: Detect the language of user-generated content or already present site content.
language-model: Run on-device natural language inference in the browser using the Prompt API, with streaming output, structured JSON responses, and multi-turn session management.
summarizer: Summarize text content using the on-device Summarizer API.
translator: Translate text between languages using the on-device Translator API.

css

animate-to-intrinsic-sizes: Smoothly animate interactive components (like accordions, menus, and expanding cards) to and from their natural dimensions.
calculate-with-intrinsic-sizes: Calculate the size of an element based on its intrinsic size, while ensuring it fits within given design constraints.
child-state-based-styling: Build a component that changes its styling based on the state of one of its child elements. For example, a component that renders in light or dark mode based on whether a theme toggle is checked (or not).
content-based-styling: Build a component that changes its layout based on whether it contains specific child elements (or not). For example, if the component contains an image, use a multi-column layout, otherwise default to a single-column layout.
design-token-reactivity: Define higher-order design tokens, like density modes (compact, comfortable, spacious) or themes and have descendant components react to changes directly and in component-appropriate ways.
dynamic-sibling-styling: Create dynamic visual spectrums or layout arrangements that automatically adapt to the number of elements in a group.
fluid-scaling: Scale items like font size, spacing, and media sizes smoothly based on the parent container's size rather than using fixed breakpoints
individual-transform-properties: Animate or override individual CSS transform properties (e.g. translate, rotate, scale) independently of other transform properties on a single element.
overflow-clipping-control: Adjust the visible clipping boundary of an element to align with the content edge, padding edge, or border edge—or a specified offset from any of these—offering finer-grained control over how content is clipped.
reduce-style-repetition: Reduce excessive style repetition by encapsulating complex or dynamic styling logic into reusable functions (such as a function that computes a gradient based on a set of input parameters).
size-aware-styling: Build a component whose styles can be conditionally dependent on its own width or height, rather than the width or height of the viewport. For example a card component that can change its layouts depending on how large it is, or a call-to-action button that can conditionally display helper text based on its width.
style-parent-with-has: Style parent elements of a form field (e.g. labels or fieldsets) when the field is invalid.
usage-aware-component-variations: Build components that adapt visual logic based on semantic context using CSS container style queries.

forms

animated-select-picker: Create a custom select component whose dropdown is animated. For example, the menu fades or slides into view, or the options animate upon selection.
autofill-address-form: Build an address form with correct autocomplete attributes and autofill support.
autofill-highlight-inputs: Use CSS to highlight form fields that have been autofilled by the browser and not edited by the user.
autofill-payment-form: Build a payment form that collects card details with correct autocomplete values and autofill support.
autofill-sign-in-form: Build a sign-in form with correct autocomplete values and autofill support.
autofill-sign-up-form: Build a sign-up form with correct autocomplete values and autofill support.
brand-consistent-forms: Match checkboxes, radio buttons, range sliders, and progress bars to your site's color palette without replacing them with custom components.
branded-select-styling: Create custom select elements whose button, picker, arrow icon, and checkmark all seamlessly match your brand or design system's typography, colors, spacing, and border treatments.
custom-select-picker-layouts: Create custom select pickers whose options are positioned in unique or interesting ways, rather than the traditional stacked list of options.
form-fields-automatically-fit-contents: Allow form fields to grow and shrink to fit the user input, e.g. as the user types or selects a different option. Apply maximum and minimum size limits to create dynamic and responsive form fields that conform with the page design.
ime-safe-enter-submit: Implement keyboard text submission (like enter-to-submit in chat/textareas) safely for IME (Input Method Editor) users to prevent premature submission of incomplete text.
required-field-feedback: Provide error message for required form fields that were skipped or left empty only after user interaction, to avoid preemptive errors and ensure feedback is timely and contextually relevant to the user's flow.
rich-media-picker: Create a custom select component whose options can contain complex HTML formatting (e.g. images, icons, and other rich formatting) rather than just plain text.
select-menu-interaction: Validate that a non-default option has been chosen in a select menu only after the user has interacted with the control.
validate-input-after-interaction: Show form field validation feedback (e.g. password complexity or email format requirements) only after the user has finished their initial interaction, avoiding premature errors on page load or while the user is typing.

js

calculate-event-differentials: Calculate the duration and time remaining between dates and times.
capture-location-agnostic-data: Record chronological data that should not change based on a user's location, such as birthdates, recurring alarms, or national holidays.
coordinate-global-events: Schedule future meetings or events by explicitly binding them to a geographical IANA time zone so that event times remain accurate regardless of Daylight Saving Time (DST) transitions, "skipped" or "repeated" hours during clock changes.
format-human-readable-durations: Present elapsed time or durations to users in a readable, localized format, with the flexibility to display either detailed unit breakdowns (e.g., "1 hour and 30 minutes") or total unit counts (e.g., "90 minutes") depending on context.
manage-recurring-intervals: Calculate recurring intervals for subscription billings or payroll cycles, automatically adjusting for edge cases such as month-end transitions (e.g., adding one month to January 31st) to ensure accurate period calculations.
model-partial-time-concepts: Model date and time concepts that inherently lack a standard component (such as a specific year, day, or date) without using arbitrary placeholder values that introduce calculation errors.
stabilize-reactive-state: Manage task deadlines or schedules in data-driven views without unexpected side effects from shared mutable state.
support-global-calendar-systems: Display and calculate dates in non-Gregorian calendar systems (e.g., Islamic, Hebrew, or Chinese) accurately for international users.

performance

batch-analytics-events: Debounce and batch multiple analytics events together in a single beacon to minimize network contention and reduce server load, while still delivering real-time updates.
break-up-long-tasks: Break up heavy synchronous processing (complex computations and/or long loops) or DOM updates, to let the browser handle user input and repaint the screen.
calculate-total-foreground-time: Calculate the total time a user actually spent viewing a page, excluding periods when the tab was in the background.
conditional-async-dependencies: Conditionally load or initialize async dependencies (such as importing polyfills for missing web features) without requiring complex orchestration across all of a page's script dependencies.
defer-rendering-heavy-content: Reduce rendering times in content-heavy web pages (e.g. pages with long feeds, lots of articles, or complex dashboards), by deferring rendering for any content that is not immediately visible to the user.
defer-work-until-scroll-ends: Defer expensive operations like DOM updates, data fetching, analytics tracking, or layout recalculation until after scrolling completes to maintain smooth scroll performance.
deliver-optimized-decorative-images: Deliver optimized decorative images (such as backgrounds, UI icons, or complex masks) by simultaneously providing next-generation image formats (like AVIF or WebP) alongside multiple pixel densities (like 1x and 2x) so the browser can dynamically negotiate the best combination of file size and visual quality for the user's device capabilities.
deprioritize-background-fetches: Deprioritize background data fetches made with the Fetch API to prevent network contention with user-initiated requests.
detect-initial-visibility-state: Reliably determine whether a page was initially loaded in the background, even in cases where the script is loaded asynchronously after the user foregrounded the page.
efficient-background-processing: Conserve system resources and battery life by pausing background JavaScript execution (such as <canvas> animations, WebGL rendering, or high-frequency WebSocket data polling) when the component is off-screen and then resume them just-in-time when they scroll back into view.
faster-spa-view-transitions: Enable faster transitions back to previously visited views in a Single-Page Application (SPA) by preserving their structural DOM state instead of destroying and rebuilding them on every navigation.
flicker-free-client-side-ab-testing: Deliver and render A/B tests, multi-variate tests, or other experiments using client-side JavaScript to alter or inject HTML, CSS, and JavaScript without the original content showing first before flickering or flashing to show the experiment content.
full-session-analytics: Reliably track analytics, errors, and telemetry data across the user's entire page visit, and defer sending of the data until the user leaves the page.
identify-heavy-scripts: Identify the scripts most responsible for long animation frames
identify-inp-causes: Identify slow running JavaScript that is impacting INP metric
improve-next-page-load-performance: Improve page load performance by prefetching or prerendering pages that the user is likely to visit next.
interactions-in-complex-layouts: Make interactions snappier and more responsive (reducing Interaction to Next Paint (INP) scores) by avoiding layout re-calculations in complex layouts, such as data-heavy dashboards or spreadsheet-style grids.
optimize-image-priority: Optimize the loading priority of Largest Contentful Paint (LCP) candidate images and deprioritize non-critical images to reduce critical resource load delays.
optimize-preload-priority: Optimize the relative priority of preloaded content to reduce critical resource load delays.
optimize-script-priority: Optimize the loading priority of scripts by boosting critical asynchronous scripts and deprioritizing non-essential or late-body scripts to improve sequencing and reduce delays.
resolution-optimized-pseudo-elements: Use resolution-optimized images in CSS pseudo-elements (such as ::before and ::after) to reduce the number of DOM nodes.
schedule-tasks-by-priority: Schedule tasks with different priorities to ensure critical work runs first while background work is deferred.
sequence-distributed-events: Log and sequence operations in distributed microservices or high-throughput tracing environments by recording timestamps with nanosecond resolution.

privacy

privacy: Action-oriented guidelines for web developers to implement privacy by design, data minimization, third-party audits, and secure data handling. Use this skill when designing applications, integrating third-party services, handling user data, or configuring security headers.

security

passkey-authentication: Authenticate a returning user with a passkey for primary sign-in.
passkey-conditional-create: Silently register a passkey for an existing user after a successful password login.
passkey-management: Let users view and manage the passkeys registered to their account.
passkey-reauthentication: Verify a signed-in user's identity using their existing passkeys before a sensitive action.
passkey-registration: Register a passkey for an existing user account.
passkeys: Comprehensive orientation and cross-cutting principles for implementing WebAuthn and Passkeys in web applications. Use this guide when handling passkey registration, authentication, management, or reauthentication.

ui-atoms

carousel-slide-effects: Create a carousel of slides with images or other visual elements, where each slide animates as they enter/center/exit their scroller. For example, the slides may fade-in/fade-out, rotate, get bigger or smaller, etc.
component-specific-light-dark-theme: Force certain elements to be in light mode or dark mode (e.g. code blocks, media players, etc) independently of the page's color-scheme.
position-aware-tooltips: Build tooltips and popovers with directional arrows (or other visual styling) that automatically point the correct way when the element flips to a fallback position.
pull-to-reveal: Build a pull-to-reveal feature that would enable the user to pull down on the screen to reveal more content, like a search bar.
resilient-context-menus-and-nested-dropdowns: Build accessible, responsive menus, tooltips, dropdowns, or contextual overlays that must be tethered to specific UI elements, guaranteeing that the overlay automatically repositions itself (e.g., flipping axes) when it encounters viewport edges, ensuring it never gets cut off.
scroll-position-aware-elements: Build floating buttons or widgets (back-to-top, scroll-to-bottom, chat launchers, etc.) that appear and disappear based on whether the user has scrolled at all.
scroll-progress-indicator: Create a scroll progress bar, stepped progress tracker, or any visual affordance that communicates how far through a page or section the user has scrolled.
scrollability-affordance-hints: Build scroll-shadow overlays, gradient fades, or directional arrow indicators that appear only when there's actually more content to scroll to in that direction.
shrinking-header-on-scroll: Smoothly animate a fixed header or full-page cover on scroll to dynamically shrink, gain shadows, and transform its layout over a predefined scroll distance.
state-aware-sticky-headers: Build sticky section headers or navbars that visually transform when they're actually "stuck" at the top, changing their color scheme or gaining a shadow.

ui-behaviors

anchor-positioning-tab-underline: Transition an element seamlessly between two target element positions. For example, moving a selected tab underline between the previously selected tab and the currently selected tab.
animate-element-entry-exit: Smoothly hide/show elements as they are added/removed from the DOM or as their display values are toggled.
animate-to-from-top-layer: Animate elements such as dialogs, popovers, and tooltips as they're entering/exiting the top layer.
carousel-snap-highlights: Visually highlight the currently snapped non-interactive item in scroll-snapping carousels, galleries, or full-page swipe experiences. For example, expanding a card when snapped, or revealing hidden content.
consistent-cross-document-transitions: Ensure critical page state is loaded and stable before initiating a cross-document view transition. This means critical CSS styles are loaded and applied, critical JavaScript is loaded and run, and the HTML visible for the user's initial view of the page has been parsed before the transition runs.
cross-document-transitions: Create smooth, seamless transitions between full page navigations, such as cross-fades, custom reveal effects, or morphing of content from one page to the next.
custom-button-actions: Declaratively connect a button to any element to trigger custom, application-specific actions using declarative button commands, invoker commands, button commands, custom commands, or declarative toggle actions.
declarative-dialog-popover-control: Toggle the visibility of a dialog or popover from a button without writing JavaScript.
directional-navigation-transitions: Animate visual state changes to reflect the direction of a user's navigational flow, such as sliding new content in from the right when advancing forward or from the left when returning to a previous screen.
dynamic-sibling-animations: Stagger animation or transition timing across sibling elements so each one starts after a computed delay based on its position in the sibling list.
group-element-transitions: Transition a group of similar elements simultaneously using the same transition logic, such as removing a product from a shopping cart and having all the other products animate into their new positions.
highlight-text-ranges: Highlight arbitrary text ranges on a page such as search results, spelling errors, or collaborative editing cursors.
interactive-content-reveal: Create interactive reveal effects, such as a spotlight that follows the user's pointer to uncover details within an image or UI section.
interest-triggered-action-previews: Show a live preview of a button's effect when a user signals interest (e.g. hovering, focusing, or long-pressing) but before they commit to clicking.
interest-triggered-tooltips: Show a tooltip or supplemental information when a user hovers over, focuses on, or long-presses an interactive element, without requiring a click.
light-dismiss-a-dialog: Create a modal dialog that can be closed via light dismiss (i.e. clicking or tapping outside of the dialog)
move-dom-element-without-losing-state: Move or reparent a DOM element without losing important element state, such as interactivity states (:focus/:active), <iframe> loading state, animation/transition state, etc
parallax-scroll-effects: Create scroll-based effects (such as parallax) where foreground and background layers move at different rates, creating a sense of depth as the user scrolls.
persistent-top-layer-ui: Keep a modal dialog, fullscreen element, or native popover visibly open and functionally active when its underlying DOM node is moved or reparented in the DOM.
physics-based-easing: Create custom, physics-based animation and transition effects, like bounce and spring, that feel more natural and engaging than traditional easing curves.
platform-controls-dismiss-dialog: Create a modal dialog that can be closed via standard platform-specific user actions, such as pressing the Esc key on desktop platforms, or a "back" or "dismiss" gesture on mobile platforms
same-document-transitions: Visually connect persisting elements across different page states or navigations in a Single Page Application (SPA) (e.g. expanding a product thumbnail into a full-bleed hero image) by smoothly morphing their size, position, or other styling properties.
scroll-entry-exit-effects: Create fade-in, scale-up, or other complex reveal-type effects on elements as they enter and exit the scrollport (or viewport) while the user is scrolling.
scroll-snap-realtime-feedback: Provide real-time visual feedback in linked UI elements while a user scrolls through snap-aligned content, before the scroll gesture completes.
scroll-snap-state-sync: Synchronize navigation indicators, linked content panels, and analytics tracking with the actively snapped item in a scrollable container.
scroll-target-on-load: Build a scrollable list of elements (e.g. a carousel of images or a chat conversation thread) that can be displayed with a particular element scrolled into view on the initial render.
scrollytelling: Animate visual properties on a target element — such as fading a backdrop, shifting a background color, or to create scrollytelling experiences — driven entirely by the scrollport position of a completely different element.
search-hidden-content: Hide content from view using patterns such as accordions, tabs, and "Read more" sections, while ensuring the hidden text reveals itself during native "Find in page" searches, allows search engine indexing, supports URL fragment deep links, and maintains ARIA accessibility.
swipe-to-remove: Let users act on items in a list (remove, archive, mark as read, etc.) with a horizontal swipe gesture, so they can process entries quickly without tapping a separate control.

ui-components

navigation-drawer: Create a navigation drawer component that, when triggered from a menu button, slides in from the side overlayed on top of existing page content, and slides out when dismissed (by swiping away, tapping outside, or pressing escape).
persistent-app-tours: Create persistent onboarding walkthroughs using tethered native overlays that stay open during user interaction.
persistent-toast-notifications: Create non-intrusive toast and overlay notifications for persistent, stackable messaging and state communication.
stack-drill-down: Build full-screen hierarchical navigation that lets users drill down into nested views and swipe or navigate back to return, with browser history kept in sync.

visual-design

adapt-scrollbar-to-contrast-preferences: Enhance scrollbar visibility for users who prefer high-contrast interfaces
apply-webgl-shaders: Apply custom visual effects with WebGL shaders to HTML content.
complex-shapes: Clip elements and their content to any free-form shape, like a symbol, brush stroke, or organic texture for more expressive designs.
customize-scrollbar-color-and-thickness: Customize the color or thickness of a scrollbar
dark-mode: Implement dark mode support in a way that respects the user's light/dark theme preference and adapts browser UI (e.g. scrollbars, form controls, etc)
export-html-media-from-canvas: Capture and export dynamic HTML content as images or video frames from within canvas.
expose-canvas-content-to-browser-features: Expose content rendered in a canvas to browser features like assistive technologies, translation, or reading mode.
improve-text-layout-and-legibility: Improve the layout and legibility of short standalone text content, such as headings no longer than a few lines, by enabling the browser to apply evenly balanced line breaks when wrapping text.
interactive-content-in-3d-scenes: Integrate interactive HTML elements into a 3D scene.
precise-text-alignment: Achieve precise vertical alignment with text of any font. For example, exactly equal visual padding above and below text, or aligning text perfectly flush with adjacent icons or images.
prevent-text-wrapping: Ensure the browser does not insert line breaks into text and will allow text to overflow its container.
shaped-cutouts: Combine multiple shapes to create complex cutouts or 'knockout' effects in elements, such as adding a notch to an element.
soft-edge-content-fade: Apply a transparency gradient to content edges to indicate further scrollable areas or to obscure payment-walled text.
visually-stable-font-fallbacks: Define font styles such that text remains readable and visually consistent in the event that there's a swap between the perferred font and one of the fallbacks (or vise versa).
visually-stable-mixed-fonts: Define font styles such that text remains readable and visually consistent in situations where multiple fonts are used to render a single block of text.
visually-texture-content: Apply realistic weathering and texture patterns to elements to give them an organic, aged, or physical material appearance.

webmcp

agentic-forms: Expose client-side functionality as tools to AI agents by annotating standard HTML forms with WebMCP attributes.
agentic-javascript-tools: Programmatically register client-side JavaScript functions as tools for AI agents using the WebMCP Imperative API.

Safe Adoption of Modern Features

Progressive Enhancement & Nuanced Fallbacks: We distinguish between purely additive enhancements (like speculative preloading) which are safe to let older browsers silently ignore, and critical behaviors (like dialog controls or network beacons) where we write highly considered, low-overhead fallbacks.
Responsible Fallbacks: We prioritize lightweight, case-specific custom fallbacks (<50 LOC) or conditionally-loaded polyfills instead of heavy third-party bundles.
Gotchas & Quirks: We document hidden platform limitations, such as the 64KB payload quota for fetchLater() or macOS-specific scrollbar behaviors.
Baseline-Aware Integration: We leverage real-time compatibility data from the Baseline project so agents can dynamically adapt to current browser support and any browser support preferences.

How It Works

Activation: The coding agent activates the modern-web-guidance skill because of a relevant task. The agent is instructed to use the modern-web-guidance CLI for web platform queries.
Local Semantic Search: The agent runs modern-web-guidance search "<query>". The tool matches the query to the best guide using an offline, CPU-efficient TensorFlow.js model (no network calls, no API keys).
Guide Fetch: The agent retrieves the guide via modern-web-guidance retrieve <guide-id>, inserting targeted code patterns, gotchas, and fallbacks directly into its context window.

Tip

Note: We use npx to ensure the content doesn't go stale, but the CLI works offline, completely private and local. The npm package is self-contained, with no extra dependencies to ensure both low-latency and supply-chain security.

Alternative Installation Methods

Vercel Skills CLI (aka npx skills)

npx skills add GoogleChrome/modern-web-guidance

GitHub CLI

gh skill install GoogleChrome/modern-web-guidance

Google Antigravity

agy plugin install https://github.com/GoogleChrome/modern-web-guidance

GitHub Copilot CLI

/plugin marketplace add GoogleChrome/modern-web-guidance
/plugin install modern-web-guidance@googlechrome

Claude Code Plugin

/plugin marketplace add GoogleChrome/modern-web-guidance
/plugin install modern-web-guidance@googlechrome
/plugin  # Select GoogleChrome marketplace, press enter, enable AutoUpdate
/reload-plugins

Grok Build CLI

grok plugin install https://github.com/GoogleChrome/modern-web-guidance --trust

Kimi Code

/plugins install https://github.com/GoogleChrome/modern-web-guidance

Updating

If you installed the skill using npx modern-web-guidance@latest install, you can update with: npx modern-web-guidance@latest update.

Otherwise, consult your agent's documentation for updating plugins and skills.

Evals to prove this works well ;)

We developed a robust eval harness to ensure that the content is empirically proven and continuously calibrated to ensure AI agents write better code. We run automated evaluations using a closed-loop validation pipeline:

  [ Expert-authored guidance and demo ]
            │
            ▼
  [ Generated assets ] ──> Playwright Grader (.spec.ts) & Negative Demo (.html)
            │
            ▼
  [ Calibration loop ] ───────> Runs Grader on Gold-Standard Demo (Must Pass 100%)
            │                   Runs Grader on Negative Demo (Must Fail 100%)
            ▼
  [ E2E agent evals ] ────────> Runs coding agents in guided vs. unguided modes
                                Compares accuracy w/ and w/o the skill

Simulated Developer Tasks: We define realistic, developer prompts that mimic real-world requests (e.g., "make my images load faster"). The prompts avoid naming APIs or features, testing whether the agent can successfully discover the relevant guides naturally.
Browser-based Assertions: We write browser automation scripts that verify the guide was followed correctly: exact runtime behaviors, computed styles, accessibility states, etc.
Self-Healing Calibration: Graders are calibrated against both a reference implementation (100% pass target) and a control page (0% pass target). The agent automatically refines tests on failure.
E2E Testing: We measure coding agent performance on real tasks with and without guidance. The opportunity (100% - unguided pass rate) and uplift (guided - unguided pass rate) are key. If there's little opportunity, then models already do a great job and our guidance isn't providing much value. Based on the results, we revise guides to maximize the uplift, optimizing their effectiveness.

Recent eval results snapshot

Date	Agent + Model	Tasks / Assertions	Unguided → Guided (Uplift)
Aug 24	claude_code (opus-5)	131 / 1033	57% → 92% (+35pp)
Aug 24	antigravity (gemini-3.7-flash-medium)	131 / 1118	60% → 89% (+29pp)
Aug 21	codex_cli (gpt-5.6-sol)	131 / 1118	60% → 81% (+21pp)
Aug 21	claude_code (opus-5)	131 / 1086	57% → 90% (+33pp)
Aug 21	antigravity (gemini-3.7-flash-medium)	131 / 1118	60% → 90% (+30pp)
Aug 17	codex_cli (gpt-5.6-sol)	130 / 1112	60% → 83% (+23pp)
Aug 17	claude_code (opus-5)	130 / 1033	58% → 92% (+34pp)
Aug 17	antigravity (gemini-3.7-flash-medium)	130 / 1112	64% → 90% (+26pp)
Aug 14	codex_cli (gpt-5.6-sol)	132 / 1125	60% → 82% (+22pp)
Aug 14	claude_code (opus-5)	132 / 1036	56% → 90% (+34pp)

Available Skill Packs

You can customize which skill packs are installed using the --choose flag:

npx modern-web-guidance@latest install --choose

modern-web-guidance (~234 tokens): Comprehensive guidance on modern browser APIs, layouts, and performance.
chrome-extensions (~181 tokens): Guidance on Manifest V3, background workers, extension APIs, and Chrome Web Store publishing.

Telemetry & Privacy

Google collects anonymous usage information to improve the tool's reliability, relevance, and performance. Collected information includes installation counts, guide retrieval IDs, and CLI tool search queries generated by the agent (e.g. "dark mode scrollbar color-scheme"). Raw user prompts are not collected. You can inspect what is collected in modern-web.ts.

Tip

To Opt-Out: set the DISABLE_TELEMETRY=1 env variable in your shell profile (e.g., .bashrc or .zshrc):

export DISABLE_TELEMETRY=1

Google handles this data in accordance with the Google Privacy Policy.

Contributors

If you'd like to contribute to modern-web-guidance, please see the source repo's CONTRIBUTING.md. The modern-web-guidance repo is purely a publish target for clean skills installation.

Huge thanks to everyone who has contributed!

License

Unless otherwise noted:

Software code in this repository is licensed under the Apache License 2.0.
Documentation and guide content under guides/ are licensed under Creative Commons Attribution 4.0 International (CC-BY 4.0).

Portions of the documentation in this project are derived from MDN Web Docs by Mozilla Contributors and W3C, WHATWG, and IETF specifications.