calendar_list_calendars

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

Annotations already declare readOnlyHint=true, so the description doesn't need to restate safety. It adds useful behavioral context: the tool returns all visible calendars (not just owned ones) and that the id field is what matters for downstream operations. This goes beyond the structured annotations without contradicting them.

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 short sentences with no filler. The first sentence front-loads the core purpose, and the second explains when it is needed. Every word earns its place.

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, read-only list tool, the description covers what is returned (all visible calendars and their ids) and why it matters (prerequisite for non-primary work). It doesn't detail every return field, but the id is the critical piece for the stated use case, so the information is adequate.

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 and schema coverage is 100%, so there is nothing for the description to add about parameters. The baseline for 0 params is 4, and the description appropriately focuses on the return value instead.

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 tool lists every calendar visible to the account and returns its id. This is a specific resource (calendars) with a clear action, and it distinguishes itself from sibling tools like calendar_list_events by focusing on calendar metadata rather than events.

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 second sentence provides explicit usage guidance: 'Needed before working on anything other than primary.' This tells an agent when to call this tool before other calendar operations, such as calendar_create_event or calendar_update_event, which would require a valid calendar id.

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