> ## Documentation Index > Fetch the complete documentation index at: https://docs.actx0.com/llms.txt > Use this file to discover all available pages before exploring further. # Create Message > Store a session message. `meta` must be a JSON string if provided; responses return parsed JSON. ## OpenAPI ````yaml /openapi.yaml post /workspaces/{workspaceId}/agents/{agentId}/sessions/{sessionId}/messages openapi: 3.1.0 info: title: Actx0 API version: 1.0.0 description: >- REST API for Actx0 workspaces, access keys, agents, sessions, messages, memories, prompts, and knowledge documents. Authenticate with `X-Access-Key` (workspace), `X-API-Key` (user), or a dashboard session. servers: - url: https://app.actx0.com/api/v1 description: Actx0 cloud security: [] tags: - name: Me description: Inspect the authenticated access key or API key - name: API Keys description: User API keys for X-API-Key auth - name: Workspaces description: Team workspaces - name: Access Keys description: Scoped workspace keys for agents and SDKs - name: Agents description: Agents inside a workspace - name: Sessions description: Agent conversation sessions - name: Messages description: Session messages and semantic search - name: Memories description: Session memories, search, batch, and regenerate - name: Prompts description: Versioned prompts - name: Knowledge description: Document upload and semantic search paths: /workspaces/{workspaceId}/agents/{agentId}/sessions/{sessionId}/messages: post: tags: - Messages summary: Create Message description: >- Store a session message. `meta` must be a JSON string if provided; responses return parsed JSON. operationId: createMessage parameters: - $ref: '#/components/parameters/WorkspaceId' - $ref: '#/components/parameters/AgentId' - $ref: '#/components/parameters/SessionId' requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/CreateMessageRequest' example: role: user content: I prefer dark mode in the dashboard meta: '{"source":"chat"}' responses: '201': description: Created content: application/json: schema: $ref: '#/components/schemas/Message' '400': description: Bad request content: application/json: schema: $ref: '#/components/schemas/Error' '401': description: Unauthorized content: application/json: schema: $ref: '#/components/schemas/Error' '403': description: Forbidden content: application/json: schema: $ref: '#/components/schemas/Error' '404': description: Not found content: application/json: schema: $ref: '#/components/schemas/Error' '500': description: Internal server error content: application/json: schema: $ref: '#/components/schemas/Error' security: - AccessKeyAuth: [] - ApiKeyAuth: [] x-codeSamples: - lang: curl label: curl / acli source: > curl -X POST 'https://app.actx0.com/api/v1/workspaces//agents//sessions//messages' \ -H "X-Access-Key: YOUR_ACCESS_KEY" \ -H "Content-Type: application/json" \ -H "Accept: application/json" \ -d '{"role": "user", "content": "I prefer dark mode in the dashboard", "meta": "{\"source\":\"chat\"}"}' # --- # acli export ACTX0_ACCESS_KEY="YOUR_ACCESS_KEY" export ACTX0_WORKSPACE_ID="YOUR_WORKSPACE_ID" acli message create "What are my preferences?" \ --agent-id AGENT_ID \ --session-id SESSION_ID \ --role user - lang: python label: pctx0 source: | from pctx0 import Pctx0Client client = Pctx0Client( access_key="YOUR_ACCESS_KEY", workspace_id="YOUR_WORKSPACE_ID", ) message = client.message.create( "AGENT_ID", "SESSION_ID", {"role": "user", "content": "What are my preferences?"}, ) - lang: javascript label: nctx0 source: > import { Nctx0Client } from "@actx0/nctx0"; const client = new Nctx0Client({ accessKey: "YOUR_ACCESS_KEY", workspaceId: "YOUR_WORKSPACE_ID", }); const message = await client.message.create("AGENT_ID", "SESSION_ID", { role: "user", content: "What are my preferences?", }); - lang: go label: gtcx0 source: "package main\n\nimport (\n\t\"context\"\n\n\t\"github.com/Actx0/Gctx0\"\n)\n\nfunc main() {\n\tclient := gctx0.NewClient(\n\t\tgctx0.WithAccessKey(\"YOUR_ACCESS_KEY\"),\n\t\tgctx0.WithWorkspaceId(\"YOUR_WORKSPACE_ID\"),\n\t)\n\tdefer client.Close()\n\tctx := context.Background()\n\tmessage, err := client.Message.Create(ctx, \"AGENT_ID\", \"SESSION_ID\", gctx0.MessageInput{\n\t\tRole: gctx0.MessageRoleUser,\n\t\tContent: \"What are my preferences?\",\n\t})\n\t_ = message\n\t_ = err\n}\n" components: parameters: WorkspaceId: name: workspaceId in: path required: true schema: type: string format: uuid example: 11111111-1111-1111-1111-111111111111 AgentId: name: agentId in: path required: true schema: type: string format: uuid example: 22222222-2222-2222-2222-222222222222 SessionId: name: sessionId in: path required: true description: Internal session UUID (not externalId). schema: type: string format: uuid example: 33333333-3333-3333-3333-333333333333 schemas: CreateMessageRequest: type: object required: - role - content properties: role: type: string enum: - system - user - assistant example: user content: type: string example: I prefer dark mode in the dashboard meta: type: string description: Optional JSON encoded as a string. example: '{"source":"chat"}' Message: type: object required: - id - sessionId - role - content - createdAt properties: id: type: string format: uuid example: 55555555-5555-5555-5555-555555555555 sessionId: type: string format: uuid example: 33333333-3333-3333-3333-333333333333 role: type: string enum: - system - user - assistant example: user content: type: string example: I prefer dark mode in the dashboard meta: {} createdAt: type: string format: date-time example: '2026-07-01T12:00:00Z' Error: type: object required: - errorMessage properties: errorMessage: type: string example: Name is required securitySchemes: AccessKeyAuth: type: apiKey in: header name: X-Access-Key description: Workspace access key for agent/runtime integrations. ApiKeyAuth: type: apiKey in: header name: X-API-Key description: User API key for management and automation. ````