Lit vs FAST vs Stencil: Web Component Frameworks in 2026

TL;DR

Web components (Custom Elements + Shadow DOM) are the framework-agnostic way to build UI. Lit (Google) is the minimal, performant choice — a ~5 KB library that adds reactive properties and a templating system on top of native Custom Elements. FAST (Microsoft) is the enterprise design system toolkit — @microsoft/fast-element is comparable to Lit in size, but FAST's ecosystem includes @microsoft/fast-components, the reference implementation of Microsoft's Fluent design system. Stencil is the compiler approach — it produces framework-agnostic web components but also generates React, Vue, and Angular wrappers automatically. For lean, framework-agnostic components: Lit. For Microsoft Fluent ecosystem integration: FAST. For generating components that work across every framework with native wrappers: Stencil.

Key Takeaways

• Lit GitHub stars: ~18k — the most widely adopted web component library
• Lit's bundle size: ~5 KB gzipped — minimal overhead vs raw Custom Elements API
• Stencil generates framework wrappers — outputs React, Vue, and Angular bindings automatically from one codebase
• FAST powers the FluentUI Web Components — used in Microsoft 365, Teams, and Edge
• All three use TypeScript decorators — @customElement, @property, @state patterns are similar
• Stencil's compiler enables SSR — pre-rendering for SEO without a framework
• Web components work in React 19 — React finally added full web component support in React 19

Why Web Components in 2026?

Web components solve a specific problem: framework-agnostic reusability. A Lit component works in React, Vue, Angular, Svelte, and vanilla HTML without modification. This makes web components the right choice for:

• Design systems used across multiple frameworks (enterprise teams)
• Third-party widgets embedded in customer pages
• Microfrontend architectures where teams use different frameworks
• Library authors who can't predict what framework consumers use

Lit: Google's Web Component Library

Lit is Google's official web component library, used in Google's own products and the base for many design systems. It extends the browser's Custom Elements API with reactive properties and tagged template literals.

Installation

npm install lit

Basic Component

import { LitElement, html, css } from "lit";
import { customElement, property, state } from "lit/decorators.js";

@customElement("my-button")
export class MyButton extends LitElement {
  // Reflected attribute + reactive property
  @property({ type: String }) label = "Click me";
  @property({ type: Boolean, reflect: true }) disabled = false;
  @property({ type: String }) variant: "primary" | "secondary" = "primary";

  // Internal state (doesn't reflect to attribute)
  @state() private _clicks = 0;

  static styles = css`
    :host {
      display: inline-block;
    }

    button {
      padding: 8px 16px;
      border-radius: 6px;
      border: none;
      cursor: pointer;
      font-size: 14px;
      font-weight: 600;
      transition: opacity 0.15s;
    }

    button:disabled {
      opacity: 0.5;
      cursor: not-allowed;
    }

    :host([variant="primary"]) button {
      background: #3b82f6;
      color: white;
    }

    :host([variant="secondary"]) button {
      background: #f3f4f6;
      color: #374151;
    }
  `;

  render() {
    return html`
      <button
        ?disabled=${this.disabled}
        @click=${this._handleClick}
      >
        ${this.label} (${this._clicks})
      </button>
    `;
  }

  private _handleClick() {
    this._clicks++;
    this.dispatchEvent(
      new CustomEvent("my-click", {
        detail: { clicks: this._clicks },
        bubbles: true,
        composed: true,  // Cross shadow DOM boundary
      })
    );
  }
}

Reactive Properties and Updates

import { LitElement, html } from "lit";
import { customElement, property, state } from "lit/decorators.js";

@customElement("user-card")
export class UserCard extends LitElement {
  @property({ type: String }) userId = "";

  @state() private _user: { name: string; email: string } | null = null;
  @state() private _loading = false;

  // willUpdate runs when properties change before re-render
  willUpdate(changedProperties: Map<string, unknown>) {
    if (changedProperties.has("userId") && this.userId) {
      this._fetchUser();
    }
  }

  private async _fetchUser() {
    this._loading = true;
    const response = await fetch(`/api/users/${this.userId}`);
    this._user = await response.json();
    this._loading = false;
  }

  render() {
    if (this._loading) return html`<p>Loading...</p>`;
    if (!this._user) return html`<p>No user</p>`;

    return html`
      <div class="card">
        <h2>${this._user.name}</h2>
        <p>${this._user.email}</p>
      </div>
    `;
  }
}

Slots and Composition

@customElement("lit-card")
export class LitCard extends LitElement {
  static styles = css`
    .card { border: 1px solid #e5e7eb; border-radius: 8px; overflow: hidden; }
    .header { padding: 16px; background: #f9fafb; border-bottom: 1px solid #e5e7eb; }
    .body { padding: 16px; }
    .footer { padding: 12px 16px; background: #f9fafb; border-top: 1px solid #e5e7eb; }
  `;

  render() {
    return html`
      <div class="card">
        <div class="header">
          <slot name="header">Default Header</slot>
        </div>
        <div class="body">
          <slot></slot>  <!-- Default slot -->
        </div>
        <div class="footer">
          <slot name="footer"></slot>
        </div>
      </div>
    `;
  }
}

<!-- Usage in any HTML/framework -->
<lit-card>
  <span slot="header">My Card Title</span>
  <p>Card body content goes here</p>
  <button slot="footer">Action</button>
</lit-card>

FAST: Microsoft's Enterprise Web Component Foundation

FAST (@microsoft/fast-element) is the foundational layer for Microsoft's Fluent design system. It's comparable to Lit in philosophy but uses different template syntax and is deeply integrated with Microsoft's design token system.

Installation

npm install @microsoft/fast-element

Basic FAST Element

import {
  FASTElement,
  customElement,
  attr,
  observable,
  html,
  css,
  when,
} from "@microsoft/fast-element";

const template = html<FastButton>`
  <button
    ?disabled="${(x) => x.disabled}"
    @click="${(x, c) => x.handleClick(c.event as MouseEvent)}"
  >
    ${when(
      (x) => x.loading,
      html`<span>Loading...</span>`,
      html`${(x) => x.label}`
    )}
  </button>
`;

const styles = css`
  :host { display: inline-block; }

  button {
    background: ${neutralFillRest};  /* FAST design token */
    color: ${neutralForegroundRest};
    border: 1px solid ${neutralStrokeRest};
    padding: 8px 16px;
    border-radius: ${controlCornerRadius};
    cursor: pointer;
  }
`;

@customElement({ name: "fast-button", template, styles })
export class FastButton extends FASTElement {
  @attr label = "Button";
  @attr({ mode: "boolean" }) disabled = false;
  @attr({ mode: "boolean" }) loading = false;

  handleClick(event: MouseEvent) {
    if (!this.disabled && !this.loading) {
      this.$emit("button-click", { event });
    }
  }
}

FAST Design Tokens

import {
  DesignToken,
  DesignTokenChangeRecord,
} from "@microsoft/fast-foundation";

// Define custom design tokens
export const brandColor = DesignToken.create<string>("brand-color").withDefault(
  "#3b82f6"
);

export const brandColorLight = DesignToken.create<string>(
  "brand-color-light"
).withDefault("#dbeafe");

// Apply tokens to a subtree
const myElement = document.getElementById("app");
brandColor.setValueFor(myElement, "#6366f1"); // Override for this subtree

// Use in CSS
const styles = css`
  :host { background: ${brandColor}; }
`;

Fluent UI Web Components (Using FAST)

<!-- Microsoft's production FAST components -->
<script type="module">
  import { provideFluentDesignSystem, fluentButton, fluentCard } from
    "https://unpkg.com/@fluentui/web-components";
  provideFluentDesignSystem().register(fluentButton(), fluentCard());
</script>

<!-- Use Fluent components anywhere -->
<fluent-card>
  <h2>Fluent Card</h2>
  <p>Powered by FAST and Microsoft's Fluent design system</p>
  <fluent-button appearance="accent">Primary Action</fluent-button>
  <fluent-button appearance="neutral">Secondary</fluent-button>
</fluent-card>

Stencil: The Compiler for Framework-Agnostic Components

Stencil (from Ionic team) is a compiler, not a runtime library. It compiles TypeScript + JSX into standard web components AND optionally generates React, Vue, and Angular wrappers — meaning your component works natively in each framework.

Installation

npm init stencil component my-components
cd my-components
npm install

Basic Stencil Component

import { Component, Prop, State, Event, EventEmitter, h } from "@stencil/core";

@Component({
  tag: "my-input",
  styleUrl: "my-input.css",
  shadow: true,  // Enable Shadow DOM
})
export class MyInput {
  // Props from outside
  @Prop() label: string = "Input";
  @Prop() placeholder: string = "";
  @Prop() value: string = "";
  @Prop({ mutable: true }) disabled: boolean = false;

  // Internal state
  @State() private focused: boolean = false;

  // Custom events
  @Event() myChange: EventEmitter<string>;
  @Event() myFocus: EventEmitter<void>;

  handleInput(event: Event) {
    const input = event.target as HTMLInputElement;
    this.myChange.emit(input.value);
  }

  render() {
    return (
      <div class={{ "input-wrapper": true, "focused": this.focused }}>
        {this.label && <label>{this.label}</label>}
        <input
          type="text"
          placeholder={this.placeholder}
          value={this.value}
          disabled={this.disabled}
          onInput={(e) => this.handleInput(e)}
          onFocus={() => { this.focused = true; this.myFocus.emit(); }}
          onBlur={() => { this.focused = false; }}
        />
      </div>
    );
  }
}

Stencil Framework Wrapper Generation

# Build the component library with framework outputs
npx stencil build

// stencil.config.ts — configure output targets
import { Config } from "@stencil/core";
import { reactOutputTarget } from "@stencil/react-output-target";
import { vueOutputTarget } from "@stencil/vue-output-target";
import { angularOutputTarget } from "@stencil/angular-output-target";

export const config: Config = {
  namespace: "my-components",
  outputTargets: [
    // Web component (standard)
    { type: "dist", esmLoaderPath: "../loader" },

    // React wrapper (auto-generated)
    reactOutputTarget({
      componentCorePackage: "my-components",
      proxiesFile: "../my-components-react/src/components.ts",
      includeDefineCustomElements: true,
    }),

    // Vue wrapper (auto-generated)
    vueOutputTarget({
      componentCorePackage: "my-components",
      proxiesFile: "../my-components-vue/src/components.ts",
    }),

    // Angular wrapper (auto-generated)
    angularOutputTarget({
      componentCorePackage: "my-components",
      directivesProxyFile: "../my-components-angular/src/directives/proxies.ts",
    }),
  ],
};

// After build: use in React with full type safety
import { MyInput } from "my-components-react";

function ReactApp() {
  return (
    <MyInput
      label="Email"
      placeholder="Enter email..."
      onMyChange={(e) => console.log(e.detail)}
    />
  );
}

Stencil SSR / Prerendering

// stencil.config.ts — enable pre-rendering for SEO
export const config: Config = {
  outputTargets: [
    {
      type: "www",
      serviceWorker: null,
      baseUrl: "https://myapp.com",
      prerenderConfig: "./prerender.config.ts",
    },
  ],
};

// prerender.config.ts
import { PrerenderConfig } from "@stencil/core";

export const config: PrerenderConfig = {
  crawlUrls: true,  // Auto-discover URLs via links
  routes: ["/", "/about", "/products"],
  afterHydrate(document: Document, url: URL) {
    // Modify the document after hydration if needed
    document.title = `${document.title} | My App`;
  },
};

Feature Comparison

Feature	Lit	FAST	Stencil
Type	Library (~5 KB)	Library (~7 KB)	Compiler
Template syntax	Tagged template literals	HTML html tag	JSX
TypeScript decorators	✅	✅	✅
Shadow DOM	Optional	Optional	Optional
Design tokens	Theming CSS	✅ FAST tokens	✅ CSS custom props
React wrapper output	Manual	Manual	✅ Auto-generated
Vue wrapper output	Manual	Manual	✅ Auto-generated
Angular wrapper output	Manual	Manual	✅ Auto-generated
SSR / Pre-rendering	Via @lit-labs/ssr	❌	✅ Built-in
Component library	Shoelace, Lion	Fluent UI Web	Ionic
Storybook support	✅	✅	✅
Bundle size (runtime)	~5 KB	~7 KB	0 (compile-time)
GitHub stars	18k	9k	12k
Backed by	Google	Microsoft	Ionic
Learning curve	Low	Medium	Medium
Use case fit	Standalone components	Microsoft ecosystem	Multi-framework design systems

When to Use Each

Choose Lit if:

• You want the leanest runtime (~5 KB) for standalone web components
• Template literals feel natural and you don't want JSX
• Your team is building a design system for diverse framework consumers
• You want close alignment with web standards (no magic compiler)

Choose FAST if:

• You're building within the Microsoft 365 / Teams / Azure ecosystem
• You want to use or extend the Fluent design system
• FAST's design token system matches your design infrastructure
• You need deep enterprise-grade component composition patterns

Choose Stencil if:

• You need to publish a component library usable natively in React, Vue, AND Angular
• SSR/pre-rendering for SEO is required without a full framework
• Your team knows JSX and wants familiar syntax
• You're building on top of Ionic or extending the Ionic ecosystem

Ecosystem & Community

The web component ecosystem has matured significantly since 2021, driven partly by React 19's addition of full web component support. Prior to React 19, React's inability to handle custom events and complex properties from web components was a significant adoption barrier. That barrier is now removed, which has catalyzed renewed interest in building framework-agnostic component libraries with Lit, FAST, or Stencil.

Lit's community is the largest and most diverse in the web component space. Google's backing provides both engineering resources and institutional credibility. The Lit Labs incubator has produced several experimental packages including @lit-labs/ssr for server-side rendering and @lit-labs/react for React integration. The community around Lit includes several production-quality design systems: Shoelace (a complete component library), Lion (ING Bank's components), and Spectrum Web Components (Adobe's design system) all use Lit as their foundation.

FAST's community is more focused — it centers on the Microsoft ecosystem and the Fluent design language. The GitHub repository is actively maintained by the Microsoft FAST team, and the project has benefited from Microsoft's commitment to using it in production across Teams, Edge, and Microsoft 365. For developers working in Microsoft-adjacent technology stacks or building integrations with Microsoft products, FAST is the natural foundation.

Stencil's community benefits from the Ionic Framework connection. Ionic, one of the most popular mobile web frameworks, uses Stencil for its component library. This provides Stencil with a massive real-world testing ground and a large installed base of developers familiar with Stencil's patterns. The Ionic components library, which has been downloaded hundreds of millions of times, demonstrates Stencil's production viability at scale.

Real-World Adoption

Lit has been adopted by several major enterprises for their design system infrastructure. Adobe's Spectrum Web Components, which powers Adobe's creative tools in the browser, is built on Lit. Google uses Lit extensively in their own products and has published best practices for building large-scale component libraries with it. The Shoelace library has been widely adopted as a drop-in web component library that works across frameworks, demonstrating Lit's viability for general-purpose component libraries. For React-based alternatives when building component systems, see best React component libraries 2026.

FAST's most prominent production deployment is the Fluent UI Web Components library, which ships in Microsoft Edge's developer tools, Microsoft Teams' web client, and various Microsoft 365 web applications. These deployments represent hundreds of millions of end users interacting with FAST-based components daily. The design token system has been particularly well-received in enterprise design system implementations where consistency across applications is a hard requirement.

Stencil's real-world adoption story is dominated by Ionic. The Ionic Framework's component library, used in hundreds of thousands of mobile web applications built with Angular, React, and Vue, demonstrates Stencil's multi-framework wrapper generation at scale. Beyond Ionic, several enterprise teams have built internal design systems with Stencil specifically because the ability to generate React, Vue, and Angular wrappers from a single codebase solves a real organizational problem: maintaining parallel component libraries for each framework is expensive. For testing your web components, see best JavaScript testing frameworks 2026.

Developer Experience Deep Dive

All three libraries use TypeScript decorators, but the decorator semantics differ enough to cause friction when switching. Lit's @property() controls which attributes are observed and how they map to properties. FAST's @attr() and @observable() cover similar ground with slightly different configuration options. Stencil's @Prop(), @State(), @Event(), and @Listen() decorators are perhaps the most self-documenting of the three, making Stencil components easy to understand at a glance.

Template syntax is where personal preference matters most. Lit's tagged template literals (html\...`) feel natural to JavaScript developers who like string-based templating, and VS Code's Lit plugin provides syntax highlighting and type checking inside template literals. FAST's template syntax is similar but uses a function-based binding model ((x) => x.property`) that some developers find more readable for complex expressions. Stencil's JSX is familiar to any React developer, which dramatically reduces the learning curve for React-experienced teams.

Debugging web components has historically been challenging because Shadow DOM boundaries create isolation that can confuse browser DevTools. All three libraries work correctly with Chrome DevTools' web component debugging support, which shows shadow roots, custom element properties, and fires lifecycle events correctly. FAST has invested in developer tooling, including a VS Code extension that provides design token documentation inline.

Performance & Benchmarks

Web component performance at runtime is primarily determined by the browser's Custom Elements implementation, not the library. Since all three libraries compile to standard Custom Elements, their rendering performance is similar for typical use cases. The meaningful performance difference is bundle size: Lit's 5KB vs FAST's 7KB vs Stencil's 0KB runtime (all component logic is compiled into the bundle itself).

For applications loading many components, Stencil's lazy loading capability is a significant advantage. Stencil can generate a lazy loader that only loads the JavaScript for components that are actually rendered on the page. A design system with 50 components won't ship all 50 components' code to a page that only uses 5. Lit and FAST require manual code splitting to achieve similar results.

First Contentful Paint times favor Stencil for complex applications because of its prerendering capability — the HTML with placeholder content can be rendered server-side and hydrated client-side. Lit's @lit-labs/ssr provides similar capabilities but requires more configuration. FAST lacks comparable SSR support.

Migration Guide

Migrating from raw Custom Elements to Lit:

Lit is designed as a thin enhancement layer over Custom Elements, so migration is additive. Extend LitElement instead of HTMLElement, replace connectedCallback/attributeChangedCallback with reactive properties and render(), and move inline styles to static styles. The migration can be done component by component without affecting consumers.

Building a multi-framework design system with Stencil:

Start with the Stencil CLI scaffold, define your component API (props, events, slots), build the Stencil components, and configure the output targets for each framework you need. The most important design decision is event naming — Stencil wraps native custom events in framework-specific event handlers, but the naming convention matters for React consumers (Stencil generates onMyEvent React props from myEvent custom events).

Adopting FAST in an existing Microsoft ecosystem project:

The key decision is whether to use FAST components directly (Fluent UI Web Components) or build custom components using @microsoft/fast-element. For Microsoft-adjacent applications (internal tools integrated with Teams, Azure, or Microsoft 365), using Fluent UI Web Components directly gives you visual consistency with the Microsoft design language at minimal development cost.

Final Verdict 2026

Web components have reached genuine production maturity in 2026. The React 19 web component support that was a longstanding blocker is resolved, and all major browsers support the Custom Elements API natively.

Lit is the correct default for most web component work. Its combination of minimal overhead, excellent TypeScript support, strong community, and Google backing makes it the safe, practical choice for building framework-agnostic components.

Stencil is the correct choice when multi-framework wrapper generation is a hard requirement. If your design system must work natively in React, Vue, AND Angular with first-class support, Stencil's compiler output is the best solution available.

FAST is the correct choice specifically for Microsoft ecosystem integration. For everyone else, Lit's simpler mental model and broader community are more valuable than FAST's design token system.

Methodology

Data sourced from GitHub repositories (star counts as of February 2026), npm weekly download statistics (January 2026), official documentation, and community discussions on the Lit Discord, FAST GitHub discussions, and StencilJS Discord. Bundle sizes measured from bundlephobia.com. Feature verification against documentation.

Related: Best React Component Libraries 2026, Best JavaScript Testing Frameworks 2026, Best Monorepo Tools 2026