> ## Documentation Index > Fetch the complete documentation index at: https://docs.checkfu.com/llms.txt > Use this file to discover all available pages before exploring further. > ## Agent Instructions > Base URL: https://api.checkfu.com. Current wire version: `2026-08-31` (`Checkfu-Version: 2026-08-31`). > Mutating HTTP requests require `Authorization: Bearer $CHECKFU_API_KEY`, `Checkfu-Version: 2026-08-31`, `Content-Type: application/json`, and `Idempotency-Key` on retriable writes. Ordinary API keys are Workspace-bound; do not send a Workspace selector header. > Core workflow: create an Agent (`POST /v1/agents`) and Environment (`POST /v1/environments`), grant `use_environment` (`POST /v1/permission-assignments`), create a Session (`POST /v1/sessions`), send events (`POST /v1/sessions/{id}/events`), stream progress (`GET /v1/sessions/{id}/events/stream`), and read the input result (`GET /v1/sessions/{id}/inputs/{input_id}/result`). > Domain model: an Agent is mutable configuration; a Session freezes its AgentVersion and Environment at creation and owns its private workspace and ordered event history. Vault stores secret credentials; Connection links an external account; ActionApproval records human approval before an action runs. > Capability status combines `audience`, `stability`, `availability`, evaluated prerequisites, and release evidence; check https://docs.checkfu.com/getting-started/status (`GET /v1/support/capabilities`) for live `available` status. # Send a message to a service entry > Sends one text message to an installed Agent through its AgentPlacement. ## OpenAPI ````yaml /openapi.json post /v1/agent-placements/{id}/messages openapi: 3.1.0 info: title: Checkfu API version: '2026-08-31' description: >- Authentication is declared per operation: API-key, runtime, or connector bearer; Automation signature; or credential-free pairing redemption. Every general Checkfu REST request requires the dated `Checkfu-Version` header (one of: 2026-08-31); the three MCP JSON-RPC transports use `MCP-Protocol-Version`, and the provider OAuth callback carries neither Checkfu header. API keys resolve one Workspace without a request selector; authenticated responses identify it with `Checkfu-Workspace-Id`. servers: - url: https://api.checkfu.com security: - bearerAuth: [] tags: - name: organizations - name: sourceRepositories - name: tenants - name: workspaces - name: principals - name: principalGroups - name: principalAccessCredentials - name: apiKeys - name: agents - name: harnessRuntime - name: permissionAssignments - name: actionPolicies - name: organizationActionPolicies - name: files - name: memoryStores - name: modelCredentials - name: modelRoutingProfiles - name: toolSources - name: skills - name: skillSources - name: skillProposals - name: instructionProposals - name: catalog - name: concepts - name: support - name: connections - name: connectionAssignments - name: connectedRuntimes - name: fileTrees - name: collaboration - name: automations - name: actionApprovals - name: standingApprovals - name: workloadReviewPolicies - name: usage - name: models - name: budgets - name: billing - name: sessions - name: audit - name: sessionExports - name: runs - name: runnerPools - name: transcripts - name: sessionWatches - name: sessionCapsules - name: sessionTrajectories - name: webhookEndpoints - name: integrationGateway - name: environments - name: vaults - name: apiMcp - name: agentPlacementMessages paths: /v1/agent-placements/{id}/messages: post: tags: - agentPlacementMessages summary: Send a message to a service entry description: >- Sends one text message to an installed Agent through its AgentPlacement. The caller authenticates with its own Principal credential and needs `invoke` on the `agent-placement` resource; every send re-checks the active placement and live PermissionAssignments. Without `session_id` the message opens its own Session; with it, it continues a Session this caller opened through the same placement while that Session waits for input. The response waits for the work to settle unless `wait` is false. An autonomous placement returns only this caller's own status and answers; a delegated placement returns the Session view its observers see. Message ids are scoped to the authenticated caller: re-sending one replays the same Session and accepts no second input. Checkfu support posture: alpha; hosted. Required evidence journey: collaboration-identity. Deployment-specific readiness and the latest proven release are available from GET /v1/support/capabilities. operationId: agentPlacementMessages.send parameters: - name: id in: path required: true schema: type: string pattern: ^aplace_[0-9a-f]{32}$ requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/AgentPlacementMessageRequest' responses: '200': description: The message's current status and the answers its caller may read content: application/json: schema: $ref: '#/components/schemas/AgentPlacementMessage' '400': description: Typed Checkfu wire error content: application/json: schema: type: object properties: type: type: string enum: - error error: type: object properties: type: type: string enum: - invalid_request_error code: type: string enum: - validation.malformed message: type: string more: type: string enum: - >- https://docs.checkfu.com/reference/errors#validation-malformed description: >- Stable public documentation and remedy for this error type. required: - type - code - message - more additionalProperties: false request_id: type: string minLength: 1 required: - type - error - request_id additionalProperties: false '401': description: Typed Checkfu wire error content: application/json: schema: type: object properties: type: type: string enum: - error error: type: object properties: type: type: string enum: - authentication_error code: type: string enum: - auth.invalid_key message: type: string more: type: string enum: - >- https://docs.checkfu.com/reference/errors#auth-invalid-key description: >- Stable public documentation and remedy for this error type. required: - type - code - message - more additionalProperties: false request_id: type: string minLength: 1 required: - type - error - request_id additionalProperties: false '403': description: Typed Checkfu wire error content: application/json: schema: type: object properties: type: type: string enum: - error error: type: object properties: type: type: string enum: - permission_error code: type: string enum: - policy.denied message: type: string more: type: string enum: - >- https://docs.checkfu.com/reference/errors#policy-denied description: >- Stable public documentation and remedy for this error type. required: - type - code - message - more additionalProperties: false request_id: type: string minLength: 1 required: - type - error - request_id additionalProperties: false '404': description: Typed Checkfu wire error content: application/json: schema: type: object properties: type: type: string enum: - error error: type: object properties: type: type: string enum: - not_found_error code: type: string enum: - validation.not_found message: type: string more: type: string enum: - >- https://docs.checkfu.com/reference/errors#validation-not-found description: >- Stable public documentation and remedy for this error type. required: - type - code - message - more additionalProperties: false request_id: type: string minLength: 1 required: - type - error - request_id additionalProperties: false '409': description: Typed Checkfu wire error content: application/json: schema: type: object properties: type: type: string enum: - error error: type: object properties: type: type: string enum: - conflict_error code: type: string enum: - runtime.invalid_transition message: type: string more: type: string enum: - >- https://docs.checkfu.com/reference/errors#runtime-invalid-transition description: >- Stable public documentation and remedy for this error type. required: - type - code - message - more additionalProperties: false request_id: type: string minLength: 1 required: - type - error - request_id additionalProperties: false '413': description: Typed Checkfu wire error content: application/json: schema: type: object properties: type: type: string enum: - error error: type: object properties: type: type: string enum: - request_too_large code: type: string enum: - validation.payload_too_large message: type: string more: type: string enum: - >- https://docs.checkfu.com/reference/errors#validation-payload-too-large description: >- Stable public documentation and remedy for this error type. required: - type - code - message - more additionalProperties: false request_id: type: string minLength: 1 required: - type - error - request_id additionalProperties: false '422': description: Typed Checkfu wire error content: application/json: schema: type: object properties: type: type: string enum: - error error: type: object properties: type: type: string enum: - invalid_request_error code: type: string enum: - runtime.harness_incompatible message: type: string more: type: string enum: - >- https://docs.checkfu.com/reference/errors#runtime-harness-incompatible description: >- Stable public documentation and remedy for this error type. required: - type - code - message - more additionalProperties: false request_id: type: string minLength: 1 required: - type - error - request_id additionalProperties: false '500': description: Typed Checkfu wire error content: application/json: schema: type: object properties: type: type: string enum: - error error: type: object properties: type: type: string enum: - api_error code: type: string enum: - runtime.internal message: type: string more: type: string enum: - >- https://docs.checkfu.com/reference/errors#runtime-internal description: >- Stable public documentation and remedy for this error type. required: - type - code - message - more additionalProperties: false request_id: type: string minLength: 1 required: - type - error - request_id additionalProperties: false components: schemas: AgentPlacementMessageRequest: type: object properties: message_id: type: string minLength: 1 maxLength: 256 pattern: ^[A-Za-z0-9._:-]+$ text: type: string minLength: 1 maxLength: 262144 session_id: $ref: '#/components/schemas/SessionId' wait: type: boolean required: - message_id - text additionalProperties: false AgentPlacementMessage: type: object properties: type: type: string enum: - agent_placement_message agent_placement_id: $ref: '#/components/schemas/AgentPlacementId' message_id: type: string minLength: 1 maxLength: 256 pattern: ^[A-Za-z0-9._:-]+$ session_id: $ref: '#/components/schemas/SessionId' status: $ref: '#/components/schemas/AgentPlacementMessageStatus' answers: type: array items: $ref: '#/components/schemas/AgentPlacementMessageAnswer' output: anyOf: - $ref: '#/components/schemas/AgentPlacementMessageOutput' - type: 'null' updated_at: type: string required: - type - agent_placement_id - message_id - session_id - status - answers - updated_at additionalProperties: false SessionId: type: string pattern: ^sess_[0-9a-f]{32}$ AgentPlacementId: type: string pattern: ^aplace_[0-9a-f]{32}$ AgentPlacementMessageStatus: type: string enum: - submitted - working - input_required - auth_required - completed - failed - canceled - rejected AgentPlacementMessageAnswer: type: object properties: event_id: $ref: '#/components/schemas/EventId' text: type: string required: - event_id - text additionalProperties: false AgentPlacementMessageOutput: type: object properties: event_id: $ref: '#/components/schemas/EventId' value: {} required: - event_id - value additionalProperties: false EventId: type: string pattern: ^evt_[0-9a-f]{32}$ securitySchemes: bearerAuth: type: http scheme: bearer ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.