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

Beyond the annotations (readOnlyHint=false, idempotentHint=true, destructiveHint=false), the description discloses the concrete dedup rule: a calendar with the same name is returned instead of a second one — real behavioral context that makes the idempotentHint actionable. It stops short of covering permission requirements or error behavior, so it is not exhaustive.

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?

Two tight sentences: the create action and parameter summary come first, then the notable dedup behavior. No filler and no repetition of the title.

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 not be explained, and the description still covers the destination (sidebar location), all parameters, and the idempotent-return rule. Nothing essential for correct invocation 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 description coverage is 33% (only freeBusyOnly is documented in the schema), so the description must compensate — and it does, naming all three inputs and spelling out the #RRGGBB colour format and the visibility effect. It omits the name length constraint (1–60), which stays only in 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 and resource ("Add a personal calendar for the user") and scopes it to "My Calendars in the calendar sidebar", which separates it from calendar.update, calendar.read and calendar.prep_brief in the sibling list. An agent knows exactly what object is created and where it appears.

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?

The purpose implies the when (user wants a new calendar), but there is no explicit guidance on alternatives such as calendar.update for existing calendars, nor any prerequisites (permissions, quotas). Usage is inferable rather than stated.

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