@mnicole-dev/calcom-mcp-server

get-available-slots

Retrieve available booking slots for an event type within a specified date range. Filter by event type ID or slug to see open times for scheduling.

Instructions

Get available booking slots for an event type within a date range.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "startTime": "<startTime>",
      "endTime": "<endTime>"
    },
    "name": "get-available-slots"
  }
}

Input Schema

Name	Required	Description
`endTime`	Yes	ISO 8601 end of the search window (e.g. 2024-09-07T23:59:59Z)
`duration`	No	Override slot duration in minutes
`startTime`	Yes	ISO 8601 start of the search window (e.g. 2024-09-01T00:00:00Z)
`eventTypeId`	No	Event type ID (use either this or eventTypeSlug)
`eventTypeSlug`	No	Event type slug (use either this or eventTypeId)

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Aug 30, 2026

TDQS

B3.1/5.0

Behavior2/5

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

There are no annotations, so the description carries the full behavioral burden. It says only that the tool gets available slots; it does not disclose pagination, timezone handling, output shape, auth requirements, or what happens when the optional eventTypeId/eventTypeSlug is omitted.

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 a single, front-loaded sentence with no filler. Every word contributes to the core action and scope.

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

Completeness3/5

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

The description is adequate for a straightforward availability query, and the schema documents all parameters. However, with no output schema and no usage/alternative guidance, there are material gaps around return format and how optional event-type selectors affect the result.

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

Parameters3/5

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

Schema description coverage is 100%, so the baseline of 3 applies. The description's 'event type' and 'date range' phrases merely echo startTime, endTime, and eventTypeId/eventTypeSlug without adding extra semantic detail beyond the schema.

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

Purpose4/5

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

The description states a clear verb and resource: it gets available booking slots, scoped to an event type and a date range. It does not, however, explicitly differentiate itself from sibling tools like get-busy-times, so it stops short of a perfect 5.

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

Usage Guidelines2/5

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

No guidance is given on when to choose this tool over get-busy-times, list-bookings, or scheduling siblings. The intended use must be inferred from the tool name and the sentence itself, with no conditions, exclusions, or alternative pointers.

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