> ## Documentation Index > Fetch the complete documentation index at: https://docs.lerian.studio/llms.txt > Use this file to discover all available pages before exploring further. # Start a monitor > Runs command under the session's repository and streams what it says into the conversation as it happens — batched on the pauses between bursts, so one test failure is one piece of news rather than forty lines. The monitor is announced in the transcript, listed until it is stopped, and killed with the host. A name already in use in this session is refused rather than replaced. ## OpenAPI ````yaml /en/openapi/v3-current/narya.yaml post /v1/sessions/{sessionId}/monitors openapi: 3.1.0 info: title: Narya Host API version: 1.0.0 description: >- The contract between the Narya host and every client. One long-lived host runs on your machine and serves this API over a Unix socket in your Narya home. Narya creates the socket owner-only, and file permissions are the whole authorization. There is no password, no token and no TLS. The terminal client and the one-shot command that Lerian ships drive this API, and a client you write drives the same one. Results never arrive on the response of the request that caused them. Submitting a message returns 202 with a turn id. Everything the turn produces streams over GET /v1/events as server-sent events with a typed envelope, and a stream resumes from a Last-Event-ID header. One error envelope: code, title, message, and fields on 422. Codes are NRY- followed by four digits. A paged list answers items, limit and a nextCursor when more remains. Cursors are opaque. servers: [] security: [] tags: - name: host description: The host process itself — version, uptime, mode, store. - name: sessions description: Durable conversation containers. Archive, never destroy. - name: messages description: Submitting work into a session and interrupting it. - name: events description: The server-sent event stream every client consumes. - name: lanes description: Parallel tracks inside a session — main, subagent, side. - name: agents description: Named recipes — instructions, tools, model, policy. Read-only in v1. - name: ladder description: >- What a person can type: the skills and command files in force for one repository, and expanding one into text. Five origins merged, nearest winning a name, the repository's own rungs gated on trust. - name: permissions description: Pending permission asks, decisions, and the decision audit. - name: intercom description: Sessions on one machine finding and messaging each other. - name: packages description: The one thing a user installs — resources, Go code, or both. - name: workflows description: Deterministic multi-agent orchestration runs. - name: providers description: Model suppliers, their auth state, and the model catalogue. - name: monitors description: >- Long-running watchers a session keeps beside its conversation — a test runner in watch mode, a build, a log being followed. Started by the model or by the person, always listed, always killable. - name: records description: The queryable local record of everything that happened. - name: schedules description: >- Work the host's own clock starts with nobody present — a repository, a prompt, a rule and what one fire may spend. Cancel, never destroy. paths: /v1/sessions/{sessionId}/monitors: parameters: - $ref: '#/components/parameters/SessionIdParam' post: tags: - monitors summary: Start a monitor description: >- Runs command under the session's repository and streams what it says into the conversation as it happens — batched on the pauses between bursts, so one test failure is one piece of news rather than forty lines. The monitor is announced in the transcript, listed until it is stopped, and killed with the host. A name already in use in this session is refused rather than replaced. operationId: startMonitor requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/MonitorStart' responses: '201': description: The monitor, now running. content: application/json: schema: $ref: '#/components/schemas/Monitor' '400': $ref: '#/components/responses/BadRequest' '404': $ref: '#/components/responses/NotFound' '409': $ref: '#/components/responses/Conflict' '422': $ref: '#/components/responses/UnprocessableEntity' '500': $ref: '#/components/responses/InternalServerError' components: parameters: SessionIdParam: name: sessionId in: path required: true description: The session's id. schema: type: string format: uuid schemas: MonitorStart: type: object description: >- A request to run a watcher. Monitors started this way are recorded as the person's; the model starts its own through its tool. required: - name - command properties: name: type: string description: >- The watcher's name. Bounded to what a URL path segment carries unchanged, because this same name is the address the request that stops the watcher is sent to. minLength: 1 maxLength: 64 pattern: ^[A-Za-z0-9][A-Za-z0-9._-]*$ command: type: string minLength: 1 maxLength: 4096 filter: type: string maxLength: 512 examples: - name: tests command: go test ./... -run Ledger filter: ^(FAIL|ok) Monitor: type: object description: One long-running watcher a session is keeping beside its conversation. required: - name - command - startedBy - startedAt properties: name: type: string description: Unique within its session; this is what stops it. command: type: string description: What runs, under the session's repository. filter: type: string description: >- A regular expression keeping only the output lines that match it. Absent means every line. startedBy: type: string enum: - model - user description: >- Which hand reached the switch. Both may, and the registry treats them identically; this says which one it was, so the model knows before it stops something it did not start. startedAt: type: string format: date-time examples: - name: tests command: go test ./... -run Ledger startedBy: model startedAt: '2026-08-23T12:01:03.000Z' Error: type: object description: >- The single error envelope every operation returns. Codes are NRY- followed by four digits and are catalogued in the top-level x-error-catalog extension. fields appears only on 422 validation errors, mapping each offending property to its problem. required: - code - title - message properties: code: type: string pattern: ^NRY-[0-9]{4}$ description: Machine-readable error code from the NRY catalogue. title: type: string maxLength: 256 description: Short human-readable summary of the error class. message: type: string maxLength: 4096 description: Specific, actionable description of what went wrong. fields: type: object description: Per-field validation problems. Present on 422 only. additionalProperties: type: string examples: - code: NRY-0002 title: Session not found message: >- No session with id 6b9f6d2e-1c3a-4f5b-9d7e-2a8c4e6f0b1d exists on this host. responses: BadRequest: description: Malformed request — invalid parameter, cursor, or JSON body. content: application/json: schema: $ref: '#/components/schemas/Error' NotFound: description: The addressed resource does not exist on this host. content: application/json: schema: $ref: '#/components/schemas/Error' Conflict: description: >- The resource's current state rejects the request — archived session, busy lane, slot conflict, failed build, already-final state. content: application/json: schema: $ref: '#/components/schemas/Error' UnprocessableEntity: description: >- The request was well-formed but failed validation. The error's fields map names each offending property. content: application/json: schema: $ref: '#/components/schemas/Error' InternalServerError: description: The host failed — including a store that refuses writes (NRY-0012). content: application/json: schema: $ref: '#/components/schemas/Error' ````