> ## Documentation Index
> Fetch the complete documentation index at: https://docs.youragentcal.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Attach a calendar as a layer

> Compose a project calendar from context calendars. Requires owner on this calendar plus read access to the layer. Re-posting the same pair returns the existing link; a new key renames it. Max 20 layers; no nesting (400 layer_depth); key collisions return 409 key_taken.



## OpenAPI

````yaml https://youragentcal.com/openapi.json post /v1/calendars/{calendarId}/layers
openapi: 3.1.0
info:
  title: AgentCal API
  version: 0.5.0
  description: >-
    The AgentCal HTTP API: calendars for AI agents. Agents mint their own
    identity and credentials, create calendars, write events, share access with
    humans and other agents, and compose calendars as layers. Plain JSON over
    HTTPS; no SDK required.


    Agent-readable quickstart: https://youragentcal.com/start.md
  contact:
    url: https://youragentcal.com
servers:
  - url: https://youragentcal.com
security:
  - agentToken: []
tags:
  - name: Identity
    description: >-
      Minting and credentials. An agent mints once, keeps the token, and can
      manage extra keys.
  - name: Calendars
    description: >-
      Create calendars and manage their settings (name, slug, timezone,
      visibility, purpose, lenses).
  - name: Events
    description: One-off, recurring, and someday events on a calendar.
  - name: Grants
    description: 'Per-calendar access for other agents: owner, writer, or reader.'
  - name: Access requests
    description: Ask for access to someone else's calendar; owners approve or deny.
  - name: Share views
    description: Filtered, capability-URL projections of a calendar at /v/{slug}.
  - name: Layers
    description: Attach other calendars as layers to compose a project calendar.
paths:
  /v1/calendars/{calendarId}/layers:
    post:
      tags:
        - Layers
      summary: Attach a calendar as a layer
      description: >-
        Compose a project calendar from context calendars. Requires owner on
        this calendar plus read access to the layer. Re-posting the same pair
        returns the existing link; a new key renames it. Max 20 layers; no
        nesting (400 layer_depth); key collisions return 409 key_taken.
      operationId: attachLayer
      parameters:
        - $ref: '#/components/parameters/CalendarId'
        - $ref: '#/components/parameters/IdempotencyKey'
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              required:
                - calendar_id
                - key
              properties:
                calendar_id:
                  type: string
                  description: cal_… id of the calendar to attach.
                key:
                  type: string
                  pattern: ^[a-z0-9](?:[a-z0-9-]{0,38}[a-z0-9])?$
                  description: >-
                    Stable handle for filters, e.g. "marketing". "main" is
                    reserved for the calendar's own events.
      responses:
        '200':
          description: The layer link.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Layer'
        '400':
          $ref: '#/components/responses/BadRequest'
        '401':
          $ref: '#/components/responses/Unauthorized'
        '403':
          $ref: '#/components/responses/Forbidden'
        '409':
          description: Layer key already in use on this calendar.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
components:
  parameters:
    CalendarId:
      name: calendarId
      in: path
      required: true
      schema:
        type: string
      description: cal_… public id.
    IdempotencyKey:
      name: Idempotency-Key
      in: header
      required: true
      schema:
        type: string
        maxLength: 200
      description: >-
        Any unique string you generate (e.g. a UUID). Required on every mutating
        POST. Retrying with the same key and body safely replays the original
        response.
  schemas:
    Layer:
      type: object
      properties:
        id:
          type: string
          examples:
            - lyr_…
        key:
          type: string
        calendar_id:
          type: string
        calendar_name:
          type: string
        calendar_slug:
          type: string
        created_at:
          type: string
          format: date-time
    Error:
      type: object
      properties:
        error:
          type: object
          properties:
            code:
              type: string
              examples:
                - invalid_request
                - unauthorized
                - insufficient_scope
                - not_found
                - slug_taken
                - last_owner
                - key_taken
            message:
              type: string
            details:
              type: object
              description: Optional extras, e.g. available slug suggestions on slug_taken.
              additionalProperties: true
  responses:
    BadRequest:
      description: >-
        Invalid request (invalid_json, invalid_request, invalid_event,
        missing_idempotency_key, last_owner, layer_depth…).
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    Unauthorized:
      description: Missing or invalid bearer token.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    Forbidden:
      description: >-
        The credential lacks a required scope, or the agent lacks a sufficient
        grant.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
  securitySchemes:
    agentToken:
      type: http
      scheme: bearer
      description: >-
        Agent token from POST /v1/mint (format ac_agent_…). Scopes: agent:read,
        calendar:read, calendar:write, grants:manage.

````