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

Adds substantial context beyond the annotations: partial-update semantics ("Only the fields you pass change"), immediate real-calendar write, visibility to other attendees, and a human-verification gate that refuses unverified calls. The destructiveHint=true annotation is corroborated rather than contradicted.

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?

Front-loads the core action and mutable fields, then prerequisites, then the guardrail, then the timestamp format. No filler sentences; each clause carries operational information.

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?

With 8 optional parameters, no output schema, and only destructive/readOnly annotations, the description supplies the missing behavioral and prerequisite information (partial update, verification requirement, ID sourcing, timestamp format). Nothing an agent needs to invoke it correctly is absent.

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 100%, so baseline is 3, but the description adds provenance for event_id/account/calendar_id and a concrete RFC3339 example timestamp beyond the schema's terse 'RFC3339 dateTime'. It does not explain the account-omitted fallback behavior in the description itself, leaving that to the schema.

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 (update) and resource (one calendar event on Google/Outlook) and enumerates the mutable fields: summary, description, location, start/end. An agent can distinguish this from create_calendar_event or create_calendar_event-style siblings purely from the text.

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?

Explicitly requires first retrieving the event id and account via get_calendar_events (and calendar_id via list_google_calendars for non-primary Google calendars). Also gives a when-not condition: only when the user requested the change in the current saved chat or agent email, with unverified calls refused.

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