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

Annotations already flag destructiveHint=true and openWorldHint=true; the description goes well beyond them by disclosing that guest-bearing events trigger notification emails and that passing attendees wholesale REPLACES the guest list, uninviting and emailing cancellations to omitted people. That is exactly the side-effect detail an agent needs before calling a destructive mutation.

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?

Five short sentences, front-loaded with the action and mutable fields, then escalating to the two risk-bearing caveats. Nothing is redundant with the schema and no sentence is filler.

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?

No output schema exists, so return behaviour is not described, but the destructive-path warnings and the recurring-series limitation cover the highest-risk unknowns. The unexplained calendarId/timeZone parameters are the only notable shortfall for an otherwise well-covered mutation tool.

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 20% (mailbox and attendees are the only documented properties), so the description must compensate. It maps title, start/end, description, location and attendees to the request, but leaves calendarId and timeZone unexplained and gives no format guidance (e.g. date-time encoding), leaving real gaps for a 10-parameter tool.

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 (Google Calendar event) and enumerates the mutable surface: title, times, description, location, guest list. It does not name the neighbouring alternatives (update_outlook_calendar_event, move_google_calendar_event) to sharpen the boundary, so it stops short of a 5.

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" gives clear partial-update semantics, and "Editing a whole recurring series is not supported" is an explicit when-not constraint. It never names a sibling tool as the alternative for cases it excludes (e.g. moving an event), so it is context-rich but not fully routing.

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