> ## Documentation Index > Fetch the complete documentation index at: https://docs.veadk.xyz/llms.txt > Use this file to discover all available pages before exploring further. # Compatibility invocation > Return results over SSE. Use prompt from a JSON object when present; other JSON values are converted to text, while non-JSON bodies are treated as raw text. User and session IDs come from request headers, defaulting to agentkit_user and an empty string; explicitly provide both The endpoint checks and creates the session automatically. The application is selected from the loaded agent, so no application name is needed in the body. It supports per-request `harness.mcp_servers` overrides but does not apply other Harness overrides. Errors after streaming starts are returned as error events Use this endpoint for text-only compatibility clients. The body is typically `{"prompt":"Hello"}`; supply the user and session in the `user_id` and `session_id` headers, rather than body fields Provide both headers explicitly to avoid grouping unrelated calls under default user or session identifiers. The service checks and creates the session, using the loaded agent application name Invocation saves the session and executes models and tools, which can incur charges or perform external actions. Resending the same message can repeat these actions The response is SSE. Read continuously with `curl -N` and handle in-stream `error` messages. For structured ADK messages, use [Run Harness with SSE](/productions/api-reference/preview/en/harness-runtime/run-sse) ## OpenAPI ````yaml productions/api-reference/openapi/en/harness-runtime.json POST /invoke openapi: 3.1.0 info: title: Harness Runtime version: agentkit-cli 0.54.0 / SDK 0.8.0 / ADK 2.2.0 description: >- Harness Runtime deployed by AgentKit CLI 0.54.0, verified with VeADK 1.0.8, AgentKit SDK 0.8.0, and Google ADK 2.2.0; scheduled tasks require separate enablement servers: - url: http://localhost:8000 description: Local server security: - {} - RuntimeBearer: [] tags: - name: Service and applications - name: Sessions - name: Agent execution - name: Artifacts - name: Memory - name: Evaluation · development server - name: Debugging · development server - name: Compatibility endpoints - name: Harness cronjobs paths: /invoke: post: tags: - Harness invocation summary: Compatibility invocation description: >- Return results over SSE. Use prompt from a JSON object when present; other JSON values are converted to text, while non-JSON bodies are treated as raw text. User and session IDs come from request headers, defaulting to agentkit_user and an empty string; explicitly provide both The endpoint checks and creates the session automatically. The application is selected from the loaded agent, so no application name is needed in the body. It supports per-request `harness.mcp_servers` overrides but does not apply other Harness overrides. Errors after streaming starts are returned as error events operationId: harnessRuntimeInvokeCompatible parameters: - name: user_id in: header required: false schema: type: string default: agentkit_user example: user-001 - name: session_id in: header required: false schema: type: string default: '' example: session-001 requestBody: content: application/json: schema: anyOf: - type: object properties: prompt: type: string description: User message for this invocation harness: $ref: '#/components/schemas/HarnessMcpOverrides' additionalProperties: true - type: array items: {} - type: string - type: number - type: boolean - type: 'null' examples: prompt: value: prompt: Hello mcp: value: prompt: Hello harness: mcp_servers: - endpoint: https://mcp.example.com/mcp text/plain: schema: type: string example: Hello responses: '200': description: SSE event stream content: text/event-stream: schema: type: string example: >+ data: {"content":{"parts":[{"text":"Hello"}]},"author":"harness_agent"} '400': description: >- Shared OAuth request combines MCP and other Harness overrides, or the request does not meet endpoint requirements content: application/json: schema: anyOf: - type: object properties: error: type: string - $ref: '#/components/schemas/ApiError' '411': description: 'Shared OAuth only: a valid Content-Length is required' content: application/json: schema: type: object properties: error: type: string example: error: CONTENT_LENGTH_REQUIRED '413': description: 'Shared OAuth only: request body exceeds 128 KiB' content: application/json: schema: type: object properties: error: type: string example: error: REQUEST_TOO_LARGE components: schemas: HarnessMcpOverrides: type: object properties: mcp_servers: items: $ref: '#/components/schemas/McpServerConfig' type: array title: Mcp Servers description: >- Remote MCP servers; omission inherits the deployment, a provided list replaces it, and an empty array disables remote MCP for this request ApiError: type: object properties: detail: type: string description: Error details required: - detail McpServerConfig: properties: protocol: type: string enum: - streamable-http - sse title: Protocol default: streamable-http description: MCP transport; defaults to streamable-http and also supports sse endpoint: type: string title: Endpoint description: >- HTTP(S) endpoint without user information, a fragment, or control characters api_key: anyOf: - type: string format: password writeOnly: true - type: 'null' title: Api Key description: >- Optional Bearer credential for the MCP service; line breaks are forbidden. This is separate from Runtime access credentials additionalProperties: false type: object required: - endpoint title: McpServerConfig securitySchemes: RuntimeBearer: type: http scheme: bearer description: >- Optional locally without a gateway; cloud deployments use the Runtime API key or user-pool JWT required by that deployment, never the model API key ````