AI SDK
ReferenceAI SDK UI

useChat

API reference for the useChat hook.

Allows you to easily create a conversational user interface for your chatbot application. It enables the streaming of chat messages from your AI provider, manages the chat state, and updates the UI automatically as new messages are received.

The useChat API has been significantly updated in AI SDK 5.0. It now uses a transport-based architecture and no longer manages input state internally. See the migration guide for details.

Import

import { useChat } from '@ai-sdk/react'

API Signature

Parameters

chat?:

Chat<UIMessage>
An existing Chat instance to use. If provided, other parameters are ignored.

transport?:

ChatTransport
The transport to use for sending messages. Defaults to DefaultChatTransport with /api/chat endpoint.
DefaultChatTransport

api?:

string = '/api/chat'
The API endpoint for chat requests.

credentials?:

RequestCredentials
The credentials mode for fetch requests.

headers?:

Record<string, string> | Headers
HTTP headers to send with requests.

body?:

object
Extra body object to send with requests.

fetch?:

FetchFunction
Custom fetch implementation. You can use it as a middleware to intercept requests, or to provide a custom fetch implementation for e.g. testing.

prepareSendMessagesRequest?:

PrepareSendMessagesRequest
A function to customize the request before chat API calls.
PrepareSendMessagesRequest

options:

PrepareSendMessageRequestOptions
Options for preparing the request
PrepareSendMessageRequestOptions

id:

string
The chat ID

messages:

UIMessage[]
Current messages in the chat

requestMetadata:

unknown
The request metadata

api:

string
The API endpoint to use for the request. If not specified, it defaults to the transport’s API endpoint: /api/chat.

messageId:

string | undefined
The message ID if applicable

prepareReconnectToStreamRequest?:

PrepareReconnectToStreamRequest
A function to customize the request before reconnect API call.
PrepareReconnectToStreamRequest

options:

PrepareReconnectToStreamRequestOptions
Options for preparing the reconnect request
PrepareReconnectToStreamRequestOptions

id:

string
The chat ID

requestMetadata:

unknown
The request metadata

api:

string
The API endpoint to use for the request. If not specified, it defaults to the transport’s API endpoint combined with the chat ID: /api/chat/{chatId}/stream.

id?:

string
A unique identifier for the chat. If not provided, a random one will be generated.

messages?:

UIMessage[]
Initial chat messages to populate the conversation with.

messageMetadataSchema?:

FlexibleSchema
Schema for validating message metadata.

dataPartSchemas?:

UIDataTypesToSchemas
Schemas for validating data parts in messages.

generateId?:

IdGenerator
A function to generate unique IDs for messages and the chat. If not provided, the default AI SDK generateId is used.

onToolCall?:

({toolCall: ToolCall}) => void | Promise<void>
Optional callback function that is invoked when a tool call is received. You must call addToolOutput to provide the tool result.

sendAutomaticallyWhen?:

(options: { messages: UIMessage[] }) => boolean | PromiseLike<boolean>
When provided, this function will be called when the stream is finished or a tool call is added to determine if the current messages should be resubmitted. You can use the lastAssistantMessageIsCompleteWithToolCalls helper for common scenarios.

onFinish?:

(options: OnFinishOptions) => void
Called when the assistant response has finished streaming.
OnFinishOptions

message:

UIMessage
The response message.

messages:

UIMessage[]
All messages including the response message

isAbort:

boolean
True when the request has been aborted by the client.

isDisconnect:

boolean
True if the server has been disconnected, e.g. because of a network error.

isError:

boolean
True if errors during streaming caused the response to stop early.

finishReason?:

'stop' | 'length' | 'content-filter' | 'tool-calls' | 'error' | 'other'
The reason why the model finished generating the response. Undefined if the finish reason was not provided by the model.

onError?:

(error: Error) => void
Callback function to be called when an error is encountered.

onData?:

(dataPart: DataUIPart) => void
Optional callback function that is called when a data part is received.

throttle?:

number
React and Vue only. Custom throttle wait time in milliseconds for reactive chat message updates. Positive values reduce UI update frequency without delaying stream processing or callbacks, and the latest messages are published before a ready or error status. Default is undefined, which disables throttling.

resume?:

boolean
Whether to resume an ongoing chat generation stream. Defaults to false.

Returns

id:

string
The id of the chat.

messages:

UIMessage[]
The current array of chat messages.
UIMessage

id:

string
A unique identifier for the message.

role:

'system' | 'user' | 'assistant'
The role of the message.

parts:

UIMessagePart[]
The parts of the message. Use this for rendering the message in the UI.

metadata?:

unknown
The metadata of the message.

status:

'submitted' | 'streaming' | 'ready' | 'error'
The current status of the chat: "ready" (idle), "submitted" (request sent), "streaming" (receiving response), or "error" (request failed).

error:

Error | undefined
The error object if an error occurred.

sendMessage:

(message?: { text: string; files?: FileList | FileUIPart[]; metadata?; messageId?: string } | CreateUIMessage, options?: ChatRequestOptions) => Promise<void>
Function to send a new message to the chat. This will trigger an API call to generate the assistant response. If a messageId is provided, the message will be replaced (useful for editing). When replacing with a CreateUIMessage, provide its id to assign a new ID to the replacement. If no message is provided, resubmits the current messages (useful after adding tool outputs).
ChatRequestOptions

headers?:

Record<string, string> | Headers
Additional headers that should be to be passed to the API endpoint.

body?:

object
Additional body JSON properties that should be sent to the API endpoint.

metadata?:

unknown
Additional data to be sent to the API endpoint.

regenerate:

(options?: { messageId?: string } & ChatRequestOptions) => Promise<void>
Function to regenerate the last assistant message or a specific message. If no messageId is provided, regenerates the last assistant message. Accepts ChatRequestOptions for headers, body, and metadata.

stop:

() => void
Function to abort the current streaming response from the assistant.

clearError:

() => void
Clears the error state.

resumeStream:

() => void
Function to resume an interrupted streaming response. Useful when a network error occurs during streaming.

addToolOutput:

(options: { tool: string; toolCallId: string; output: unknown } | { tool: string; toolCallId: string; state: "output-error", errorText: string }) => void
Function to add a tool result to the chat. This will update the chat messages with the tool result. If sendAutomaticallyWhen is configured, it may trigger an automatic submission.

addToolApprovalResponse:

(options: { id: string; approved: boolean; reason?: string }) => void | PromiseLike<void>
Function to respond to a tool approval request. The id should match the approval id from the tool call. If sendAutomaticallyWhen is configured, it may trigger an automatic submission.

setMessages:

(messages: UIMessage[] | ((messages: UIMessage[]) => UIMessage[])) => void
Function to update the messages state locally without triggering an API call. Useful for optimistic updates.

React rendering and shared Chat instances

In React, messages, status, and error describe the snapshot for the current render. The underlying Chat updates as stream chunks are processed. React may batch updates, and throttle can delay message rendering without delaying stream processing or callbacks. Status and error updates include the latest messages, so a completed or failed response is rendered with its final message snapshot.

Each useChat({ chat }) call subscribes independently. Consumers sharing a Chat can display different message snapshots when they use different throttle intervals. A functional setMessages updater receives the Chat's latest messages, which may be newer than the messages in the current render.

Learn more

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