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fettle-mcp

by fettlesh
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TypeScript

Preview a maintenance schedule

preview_maintenance_window
Read-onlyIdempotent

Preview the next three occurrences of a maintenance schedule without saving, to validate a recurring schedule before creating or updating a maintenance window.

Instructions

Compute the next three occurrences, each with start and end, that a schedule would produce, without saving anything. Use it to check a recurring schedule before create_maintenance_window or update_maintenance_window; for a saved window's occurrences use get_maintenance_window. Requires a key with the write scope. An invalid schedule is a 422 with the reason. Returns an array. Example: {"dtstart": "2026-10-18T03:00:00", "duration_minutes": 60, "rrule": "FREQ=WEEKLY;BYDAY=SU", "timezone": "Europe/Berlin"}

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
rruleNoRepeats the window: one iCal RRULE without the RRULE: prefix, at most 1024 characters, for example FREQ=WEEKLY;BYDAY=SU;BYHOUR=3. Hourly, minutely and secondly frequencies are refused. Omit it for a one-time window.
dtstartYesThe first start, an ISO 8601 date-time in the wall-clock time of timezone, for example 2026-10-14T22:00:00. A UTC offset or Z is a 422.
timezoneNoIANA zone name such as Europe/Berlin, at most 64 characters. The schedule repeats in it, so a weekly 03:00 stays 03:00 across daylight-saving changes. Defaults to the organization's timezone.
duration_minutesYesHow long each occurrence lasts, 1 to 40320 minutes.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed4 schema fields changedv0.6.1
    • addedInput schema / properties / dtstart / description
      Added value: +"The first start, an ISO 8601 date-time in the wall-clock time of timezone, for example 2026-10-14T22:00:00. A UTC offset or Z is a 422."
    • addedInput schema / properties / duration_minutes / description
      Added value: +"How long each occurrence lasts, 1 to 40320 minutes."
    • addedInput schema / properties / rrule / description
      Added value: +"Repeats the window: one iCal RRULE without the RRULE: prefix, at most 1024 characters, for example FREQ=WEEKLY;BYDAY=SU;BYHOUR=3. Hourly, minutely and secondly frequencies are refused. Omit it for a one-time window."
    • addedInput schema / properties / timezone / description
      Added value: +"IANA zone name such as Europe/Berlin, at most 64 characters. The schedule repeats in it, so a weekly 03:00 stays 03:00 across daylight-saving changes. Defaults to the organization's timezone."
  2. First observedv0.5.4

TDQS

A4.5/5.0
Behavior5/5

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

Annotations already cover read-only/idempotent/non-destructive, and the description adds context annotations cannot express: it requires a write-scoped key despite being a read, invalid schedules fail as a 422 carrying the reason, and the result is an array of three occurrences with start and end. Auth, error, and return-shape behavior are all disclosed.

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

Conciseness4/5

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

Front-loads the core behavior, then usage, auth, errors, and return shape in tight sentences. The example earns its place by showing a valid combined payload, though the entry is on the dense side.

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

Completeness4/5

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

With no output schema, the description carries the return-value burden and does state an array of start/end occurrences, plus error semantics. It is nearly complete, though it could note whether exactly three are always returned or fewer for one-time windows.

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%, and the schema already documents dtstart wall-clock semantics, the RRULE format and refused frequencies, the IANA timezone default, and the duration bounds. The description only echoes this via a sample payload, so baseline 3 is correct.

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?

States a specific verb and resource: computes the next three occurrences a schedule would produce, without saving. It also names the siblings it is not (create_maintenance_window, update_maintenance_window, get_maintenance_window), so an agent can distinguish it from every adjacent tool.

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?

Explicitly routes: use this to validate a recurring schedule before create/update, and use get_maintenance_window instead for a saved window's occurrences. Both the when-to-use and the alternative-selection condition are stated outright.

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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