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

Annotations already declare destructiveHint=true and idempotentHint=true, so the safety profile is covered. The description adds meaningful context beyond that: which attributes are mutable, that the target must be the user's own personal calendar, and that connected/shared calendars are untouched. It stops short of saying whether at least one change field is required or what happens on a permission or name-collision failure.

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?

A single well-structured sentence front-loads the mutation and its fields, then the identifier, then the exclusion. No filler, and the most consequential constraint (which calendars are not affected) is not buried.

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 an output schema present, return values need no explanation, and the description covers all four parameters plus target scoping for a small mutation tool. Minor gaps remain around the requirement to supply at least one change field and around failure modes, but nothing essential to invoking it correctly is missing.

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 25%, but the description compensates well: it disambiguates the easily-confused 'calendar' (target, by id or name) from 'name' (the new name being set), and glosses 'freeBusyOnly' as free/busy-only visibility and 'color' as #RRGGBB. That resolves the main ambiguity an agent would hit when the bare schema is all it has.

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 specific verbs (rename, change colour, change visibility) against a specific resource (the user's own personal calendar) and explicitly excludes connected Google and shared calendars, which distinguishes it from siblings like calendar.create, calendar.read, and access.update. An agent can identify the operation and its scope without opening the 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?

Gives a clear when-not condition ('Connected (Google) and shared calendars are not changed here'), which prevents a large class of mis-calls. It does not name the alternative tool an agent should use for those calendars, so the routing guidance is clear but not fully closed.

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