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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the agent knows this is a safe read operation. The description adds useful context beyond annotations by explaining the types of calendars (primary, shared, subscribed, secondary) and the importance of calendar IDs for other operations. However, it does not disclose behavioral traits like pagination details or rate limits, which are partially covered by the input schema but could be elaborated.

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?

The description is front-loaded with the core purpose in the first sentence, followed by usage guidance and additional context. Each sentence earns its place by providing value, such as explaining calendar types and ID requirements, without unnecessary repetition or fluff. It is appropriately sized for the tool's complexity.

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?

Given the tool's low complexity (list operation), rich annotations (read-only, non-destructive), and the presence of an output schema, the description is complete enough. It covers the purpose, usage context, and key behavioral insights (e.g., calendar types and ID importance), without needing to explain return values or detailed parameters, which are handled by structured data.

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 100%, with clear descriptions for both parameters (pageToken and maxResults). The description does not add any parameter-specific semantics beyond what the schema provides, such as explaining how pagination works in practice or default behaviors. Since the schema does the heavy lifting, a baseline score of 3 is appropriate.

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?

The description clearly states the specific action ('List all calendars') and resource ('calendars the user has access to'), distinguishing it from sibling tools like create_event or get_calendar_events. It explicitly mentions the purpose is to 'discover available calendars before performing calendar operations,' which is distinct from operations that manipulate events or check availability.

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 description provides explicit guidance on when to use this tool ('to discover available calendars before performing calendar operations') and implies when not to use it (e.g., for event-related operations handled by siblings). It also notes that 'The calendar ID is required for all other calendar operations,' reinforcing its role as a prerequisite step.

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