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homeassistant-ai

Home Assistant MCP Server

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Create or Update Calendar Event

ha_config_set_calendar_event
Destructive

Create a new calendar event, either one-time or recurring, by specifying summary, start, end, and optional recurrence rule.

Instructions

Create a new event in a calendar.

Creates a one-off event via the calendar.create_event service, or a recurring series via the WebSocket calendar/event/create command when rrule is provided (the REST service schema does not accept recurrence rules).

When NOT to use:

  • To retrieve calendar events, use ha_config_get_calendar_events.

  • To delete an event, use ha_config_remove_calendar_event.

Example Usage:

# Create a simple event
result = ha_config_set_calendar_event(
    "calendar.family",
    summary="Doctor appointment",
    start="2024-01-15T14:00:00",
    end="2024-01-15T15:00:00"
)

# Create a recurring event (every Monday, 10 occurrences)
result = ha_config_set_calendar_event(
    "calendar.work",
    summary="Team meeting",
    start="2024-01-15T10:00:00",
    end="2024-01-15T11:00:00",
    rrule="FREQ=WEEKLY;BYDAY=MO;COUNT=10"
)

# Create an all-day event (date-only, no time component). The end
# date is EXCLUSIVE, so this spans 2026-07-04 through 2026-07-10.
result = ha_config_set_calendar_event(
    "calendar.family",
    summary="Vacation",
    start="2026-07-04",
    end="2026-07-11"
)

Note: Passing date-only values (YYYY-MM-DD) for both start and end creates an all-day event; passing full ISO datetimes creates a timed event. The two forms cannot be mixed — a date-only start with a datetime end (or vice versa) is rejected. Because the all-day end date is exclusive, a single-day all-day event must set end to start + 1 day.

Not every calendar integration supports event creation; recurring events additionally require the integration to support recurrence (the built-in Local Calendar does).

Returns:

  • Success status and event details

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
endYesEvent end date or datetime in ISO format. For all-day events (date-only) the end date is exclusive; a single-day all-day event needs end = start + 1 day.
rruleNoOptional RFC 5545 recurrence rule, without 'RRULE:' prefix (e.g., 'FREQ=WEEKLY;BYDAY=MO' or 'FREQ=MONTHLY;BYDAY=3SA'). Creates a recurring event series.
startYesEvent start date or datetime in ISO format
summaryYesEvent title/summary
locationNoOptional event location
entity_idYesCalendar entity ID (e.g., 'calendar.family')
descriptionNoOptional event description

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already mark destructiveHint=true, but the description adds crucial context: exclusive end date for all-day events, requirement for recurrence support, and failure modes for mixed date formats. No contradiction with annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is well-organized into clear sections (purpose, when not to, examples, notes, returns). Every sentence adds value without unnecessary fluff.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given 7 parameters, 4 required, and an output schema, the description covers all critical aspects: differences between event types, integration limitations, return values, and common pitfalls (date mixing, exclusive end). A complete guide for correct invocation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so baseline is 3, but the description adds meaning through examples (all-day vs timed events, rrule format) and notes on exclusive end dates, which clarifies parameter interaction beyond the schema descriptions.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool creates calendar events, distinguishes between one-off and recurring, and explicitly contrasts with sibling tools for retrieval (ha_config_get_calendar_events) and deletion (ha_config_remove_calendar_event).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides a dedicated 'When NOT to use' section naming specific alternatives, along with multiple examples and detailed notes on date format mixing and integration support. This is explicit guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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