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

Annotations only give readOnly=false/destructive=true/openWorld=true; the description adds non-obvious side effects the annotations cannot express — that changing an event with guests emails them unconditionally, and that passing attendees silently uninvites omitted guests. This is exactly the behavioral detail that prevents a destructive mistake.

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

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

Four sentences, each front-loaded and earning its place: purpose, patch instruction, email side effect, recurring-series limitation, and the attendees replacement warning. No filler or redundancy.

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

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

For a destructive mutation with no output schema, the description covers the highest-risk behaviors (guest notification, attendee replacement, recurring-series limitation). It omits timeZone handling relative to start/end and any response expectation, but is otherwise sufficient to call the tool safely.

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

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

Schema coverage is only 22%, so the description must carry the load, and it does for the important ambiguous cases: it clarifies the field set (title, start/end, description, location, attendees) and spells out the replace-not-merge semantics of attendees. It leaves timeZone and eventId unexplained, so it doesn't fully close the coverage gap.

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

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

States a specific verb (change/update) and resource (Outlook calendar event) and enumerates the mutable fields (title, times, description, location, guest list). This clearly distinguishes it from create_/delete_/move_/get_outlook_calendar_event siblings without needing to open any schema.

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

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

"Supply only the fields to change" establishes patch semantics, and "Editing a whole recurring series is not supported" is an explicit when-not constraint. It stops short of naming an alternative tool (e.g. move_outlook_calendar_event for relocating), so routing guidance is implied rather than complete.

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