list_calendars

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

Annotations already indicate readOnlyHint true and destructiveHint false. The description adds useful context about local-only calendars and platform scope (macOS/Linux), which goes beyond the annotations. It doesn't describe return format, but for a zero-parameter list tool that's a minor omission.

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 sentences front-load the primary action and then provide actionable downstream guidance. Every word earns its place; no redundancy or filler.

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 simple zero-parameter list tool, the description is fully complete: it states what is listed, platform specificity, and how to use the results. The pointer to add_to_calendar adds pragmatic context. No output schema exists, but the return values (calendar names) are obvious from the description.

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 baseline is 4. The description adds no parameter details (properly, as none exist), and the empty input schema is fully self-documenting.

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 all available local calendars, specifying the scope as macOS Calendar.app / Linux default. This distinguishes it from sibling tools like list_events or list_accounts, and mentions the practical use of returned names with add_to_calendar.

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?

It provides explicit guidance on when to use the tool: to obtain calendar names for targeting a specific calendar in add_to_calendar. However, it does not explicitly mention when not to use it or compare with alternative list tools, so it's slightly below a perfect score.

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