> ## Documentation Index > Fetch the complete documentation index at: https://langtail.com/docs/llms.txt > Use this file to discover all available pages before exploring further. # Create Thread Message > Create a new message in a thread. Use this endpoint to add a message to a thread without calling the LLM. In most cases, you should use the [Invoke Assistant API](api-reference/endpoint/invoke-assistant) to add messages and get a response from the LLM. However, this endpoint is useful when you need to add messages without immediate LLM processing, such as for creating placeholder messages or updating thread content separately. ## OpenAPI ````yaml POST /v2/threads/{threadId}/messages openapi: 3.0.0 info: version: 1.0.0 title: Langtail prompt endpoint servers: [] security: [] paths: /v2/threads/{threadId}/messages: post: description: Create a new message in a thread. parameters: - schema: type: string example: required: true description: Your Langtail API Key name: X-API-Key in: header - name: threadId in: path required: true description: The ID of the thread. schema: type: string requestBody: required: true content: application/json: schema: type: object properties: message: type: object description: Message that will be added to the thread. properties: role: type: string enum: - assistant - user - system - function - tool name: type: string content: anyOf: - type: string description: Text content nullable: false - type: array description: Mix of text and images. items: anyOf: - type: object properties: type: type: string enum: - text text: type: string required: - type - text - type: object properties: type: type: string enum: - image_url image_url: type: object properties: url: type: string detail: type: string enum: - auto - low - high default: auto required: - url - detail required: - type - image_url - nullable: true description: >- Can be omited if there is a `function_call` or `tool_calls` function_call: type: object properties: name: type: string arguments: type: string required: - name - arguments tool_calls: type: array items: type: object properties: id: type: string type: type: string enum: - function function: type: object properties: name: type: string arguments: type: string required: - name - arguments required: - id - type - function tool_choice: anyOf: - type: string enum: - auto - type: string enum: - none - type: object properties: type: type: string enum: - function function: type: object properties: name: type: string required: - name required: - type - function tool_call_id: type: string required: - role - content metadata: type: object description: >- A set of key-value pairs that can be attached to the message. example: user_id: user_123 conversation_topic: product_inquiry priority: high required: - message responses: '200': description: Successful response content: application/json: schema: type: object properties: id: type: string description: The unique identifier for the message. createdAt: type: string format: date-time description: The timestamp when the message was created. threadId: type: string description: The ID of the thread this message belongs to. content: type: array items: type: object properties: role: type: string enum: - assistant - user - system - function - tool content: anyOf: - type: string description: Text content nullable: false - type: array description: Mix of text and images. items: anyOf: - type: object properties: type: type: string enum: - text text: type: string required: - type - text - type: object properties: type: type: string enum: - image_url image_url: type: object properties: url: type: string detail: type: string enum: - auto - low - high default: auto required: - url - detail required: - type - image_url - nullable: true description: >- Can be omited if there is a `function_call` or `tool_calls` function_call: type: object properties: name: type: string arguments: type: string required: - name - arguments tool_calls: type: array items: type: object properties: id: type: string type: type: string enum: - function function: type: object properties: name: type: string arguments: type: string required: - name - arguments required: - id - type - function tool_choice: anyOf: - type: string enum: - auto - type: string enum: - none - type: object properties: type: type: string enum: - function function: type: object properties: name: type: string required: - name required: - type - function tool_call_id: type: string required: - role - content description: >- Additional messages. These will be appended to the Prompt Template. example: - role: user content: Hello metadata: type: object description: >- A key-value store for additional metadata associated with the message. additionalProperties: type: string nullable: true requestLog: type: object description: Information about the request log, if available. properties: id: type: string description: The unique identifier for the request log. createdAt: type: string format: date-time description: The timestamp when the request log was created. request: type: object description: Details of the request made. response: type: object description: Details of the response received. nullable: true requestLogId: type: string description: The unique identifier for the request log, if available. nullable: true required: - id - createdAt - threadId '400': description: Bad request content: application/json: schema: type: object properties: error: type: object properties: message: type: string example: Invalid request parameters required: - error '404': description: Thread not found content: application/json: schema: type: object properties: error: type: object properties: message: type: string example: Thread not found required: - error servers: - url: https://api.langtail.com ````