📄 ai-sdk/docs/reference/ai-sdk-core/model-message

ModelMessage represents the fundamental message structure used with AI SDK Core functions. It encompasses various message types that can be used in the messages field of any AI SDK Core functions.

You can access the Zod schema for ModelMessage with the modelMessageSchema export.

ModelMessage Types

`SystemModelMessage`

A system message that can contain system information.

type SystemModelMessage = {  role: 'system';  content: string;};

You can access the Zod schema for SystemModelMessage with the systemModelMessageSchema export.

Using the "system" property instead of a system message is recommended to enhance resilience against prompt injection attacks.

`UserModelMessage`

A user message that can contain text or a combination of text, images, and files.

type UserModelMessage = {  role: 'user';  content: UserContent;};
type UserContent = string | Array<TextPart | ImagePart | FilePart>;

You can access the Zod schema for UserModelMessage with the userModelMessageSchema export.

`AssistantModelMessage`

An assistant message that can contain text, tool calls, or a combination of both.

type AssistantModelMessage = {  role: 'assistant';  content: AssistantContent;};
type AssistantContent = string | Array<TextPart | ToolCallPart>;

You can access the Zod schema for AssistantModelMessage with the assistantModelMessageSchema export.

`ToolModelMessage`

A tool message that contains the result of one or more tool calls.

type ToolModelMessage = {  role: 'tool';  content: ToolContent;};
type ToolContent = Array<ToolResultPart>;

You can access the Zod schema for ToolModelMessage with the toolModelMessageSchema export.

ModelMessage Parts

`TextPart`

Represents a text content part of a prompt. It contains a string of text.

export interface TextPart {  type: 'text';  /**   * The text content.   */  text: string;}

`ImagePart`

Represents an image part in a user message.

export interface ImagePart {  type: 'image';
  /**   * Image data. Can either be:   * - data: a base64-encoded string, a Uint8Array, an ArrayBuffer, or a Buffer   * - URL: a URL that points to the image   */  image: DataContent | URL;
  /**   * Optional IANA media type of the image.   * We recommend leaving this out as it will be detected automatically.   */  mediaType?: string;}

`FilePart`

Represents an file part in a user message.

export interface FilePart {  type: 'file';
  /**   * File data. Can either be:   * - data: a base64-encoded string, a Uint8Array, an ArrayBuffer, or a Buffer   * - URL: a URL that points to the file   */  data: DataContent | URL;
  /**   * Optional filename of the file.   */  filename?: string;
  /**   * IANA media type of the file.   */  mediaType: string;}

`ToolCallPart`

Represents a tool call content part of a prompt, typically generated by the AI model.

export interface ToolCallPart {  type: 'tool-call';
  /**   * ID of the tool call. This ID is used to match the tool call with the tool result.   */  toolCallId: string;
  /**   * Name of the tool that is being called.   */  toolName: string;
  /**   * Arguments of the tool call. This is a JSON-serializable object that matches the tool's input schema.   */  args: unknown;}

`ToolResultPart`

Represents the result of a tool call in a tool message.

export interface ToolResultPart {  type: 'tool-result';
  /**   * ID of the tool call that this result is associated with.   */  toolCallId: string;
  /**   * Name of the tool that generated this result.   */  toolName: string;
  /**   * Result of the tool call. This is a JSON-serializable object.   */  output: LanguageModelV2ToolResultOutput;
  /**  Additional provider-specific metadata. They are passed through  to the provider from the AI SDK and enable provider-specific  functionality that can be fully encapsulated in the provider.  */  providerOptions?: ProviderOptions;}

`LanguageModelV2ToolResultOutput`

export type LanguageModelV2ToolResultOutput =  | { type: 'text'; value: string }  | { type: 'json'; value: JSONValue }  | { type: 'error-text'; value: string }  | { type: 'error-json'; value: JSONValue }  | {      type: 'content';      value: Array<        | {            type: 'text';
            /**          Text content.            */            text: string;          }        | {            type: 'media';
            /**          Base-64 encoded media data.            */            data: string;
            /**          IANA media type.          @see https://www.iana.org/assignments/media-types/media-types.xhtml            */            mediaType: string;          }      >;    };

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AssistantModelMessage