The core SDK (@leuria/client)

A site writes each AI feature once. For each request, the SDK picks the best AI this visitor has.

import { createLeuria, bridge, browserAI, server, defineTool } from "@leuria/client"

const ai = createLeuria({
  providers: [
    bridge({ app: "Mug shop" }),                      // the visitor's own AI, through the Leuria engine
    browserAI(),                                      // the browser's built-in model (Chrome's Prompt API)
    server({ url: "/api/ai/chat/completions" }),      // your server, as the last resort
  ],
})

const searchProducts = defineTool<{ query: string }>({
  name: "search_products",
  description: "Search products; returns name, price and stock.",
  inputSchema: { type: "object", properties: { query: { type: "string" } } },
  execute: ({ query }) => catalog.search(query),      // runs in the page
})

const convo = ai.conversation({ system: "You are the shop's assistant. Use the tools; never guess.", tools: [searchProducts] })
for await (const event of convo.send("Which mug is cheapest?")) {
  if (event.type === "text-delta") output.textContent += event.text
}

How it fits together

• Providers, in order of preference. The visitor's own AI through Leuria, the browser's model, your server, or your own. Each request goes to the first one that is ready and can do what the request needs. Nothing ready? The state says what a click would fix.
• The page owns the work. Tools run in the page, whichever provider answers. The history belongs to the page too, so a conversation moves to a better AI as soon as the visitor connects one.
• Plain state. The client and each conversation expose an immutable snapshot and a subscribe(). Any UI framework, and adapters such as React's, follow them directly.

Guides

Guide	What
Providers and the cascade	The built-in providers, how one is picked, routing, NoProviderError, the client's state, connecting
Conversations and turns	ai.chat() and ai.conversation(), turn context, queue, timeouts, warm sessions, events, attachments, the conversation's state
Page tools	defineTool, tool context, terminal tools, tools the visitor answers, middleware, WebMCP
Structured output	A JSON Schema in, a parsed and validated object out, from any provider
Embeddings and search by meaning	ai.embed(), @leuria/store and a model in the page with @leuria/web-embed
Connect UI	The connect flow, and Leuria's elements for any page or for React
React	@leuria/react hooks
Custom providers	Plug another model or API into the cascade

The engine's own API, for writing another client, is the engine protocol.

Packages

Package	What
@leuria/client	The SDK: providers, conversations, tools, structured output, embeddings
@leuria/connect	The Connect UI as web components, for any page and framework
@leuria/react	React hooks on the client's state
@leuria/react-connect	The Connect UI elements as React components
@leuria/store	Search by meaning in the visitor's browser
@leuria/web-embed	A small embedding model in the page

The live demos use them: a shop (in React and in plain HTML), a notes site with search by meaning and a field guide with a team builder. Their code is in leur-ia/demo.