Menu
Language
Theme
Svelte 5 SDK for Deep Agents, LangChain and LangGraph.
useStream binds a LangGraph agent into a Svelte 5 component. Reactive fields are exposed as getters on a stable handle (stream.messages, stream.isLoading, …) so templates and $derived expressions track updates automatically — no stores, no $ prefix, no destructuring.
npm install @langchain/svelte @langchain/corePeer dependencies: svelte ^5.0.0, @langchain/core ^1.0.1
<script lang="ts">
import { useStream } from "@langchain/svelte";
const stream = useStream({
assistantId: "agent",
apiUrl: "http://localhost:2024",
});
</script>
{#each stream.messages as msg (msg.id)}
<div>{msg.content}</div>
{/each}
<button
disabled={stream.isLoading}
onclick={() =>
stream.submit({ messages: [{ type: "human", content: "Hello!" }] })}
>
Send
</button>Note: Access fields through the live
streamhandle. Destructuring (const { messages } = stream) freezes the values at that moment — usestream.messagesin templates instead.
reconnectOnMount / joinStream dance.values, messages, toolCalls, and interrupts are reactive at the root with zero extra subscription cost.threadId. Pass threadId: () => active to drive in-place thread swaps without remounting.useStream<typeof agent>() unwraps state, tool calls, and subagent state maps from an agent brand.In-depth guides live in docs/:
useStream — options, return shape, reactive threadIduseMessages, useToolCalls, useValues, …)respond(), stop(), hydrationPromiseprovideStream / getStream)AgentServerAdapter, HttpAgentServerAdapter)@langchain/svelte v1 targets the v2 streaming protocol. The useStream import stays the same, but the option bag, return shape, and how you subscribe to scoped data all change. Most chat apps migrate in well under an hour — the full guide with line-by-line diffs lives in docs/v1-migration.md.
For full end-to-end examples, see the LangChain UI Playground.
MIT
Public v1 name for TransportAdapter plus optional high-level capabilities. Renamed to reflect that this interface now denotes the full agent-server protocol contract (not merely wire transport): any o
Typed error thrown through media.stream / rejected from
media.blob / media.objectURL when a handle fails before its
message completes. Carries the bytes accumulated up to the failure
point on `p
Strip headless-tool interrupts from a user-facing interrupt list.
Execute and resume all newly seen headless-tool interrupts from a values
payload. Callers own handledIds and should clear it when the thread changes.
Reads the shared stream handle exposed by the nearest ancestor provideStream call. Throws when no ancestor has provided one.
Parses a headless-tool interrupt value from the graph. Accepts both
toolCall (LangChain JS) and tool_call (Python / JSON snake_case).
Creates a shared useStream handle and publishes it via
Svelte's setContext. Descendant components read it via
getStream.
Must be called during component initialisation (the top level of a `