List calendars

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

There are no annotations, so the description carries the full burden. It clarifies the scope ('available to the account') and the output content, but since it is a list operation with no side effects, the read-only nature is strongly implied by the name. It does not explicitly state auth requirements or whether the output is a flat array, which an output schema may cover.

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 with no filler. The core purpose is front-loaded, and the usage guidance is concise and actionable.

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?

For a zero-parameter discovery tool, the description is complete. It states what is returned, the scope, and how the result feeds into sibling tools. The output schema is present, so detailed return structure does not need to be repeated.

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?

The tool has zero parameters, so the description does not need to explain parameter behavior. It adds value by telling the agent what the output will be useful for, specifically the `calendar_name` consumed by event tools.

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 states a specific action ('List the iCloud calendars available to the account') and resource, plus the returned data ('names and CalDAV URLs'). It clearly differentiates this from the sibling event-focused tools by emphasizing calendar discovery rather than event operations.

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 explicitly tells the agent when to use this tool: to discover the exact `calendar_name` expected by `create_event` and `list_events`. This gives a concrete, actionable purpose and names the dependent sibling tools.

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