apple_calendar_list_calendars

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

The description explicitly labels the tool as 'Read-only,' matching the annotations (readOnlyHint=true, destructiveHint=false, idempotentHint=true). It adds valuable context by specifying the output includes calendar names and writable status, which goes beyond what the annotations convey. No contradictions.

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 a single, well-structured sentence. It front-loads the 'Read-only' behavior, states the resource and output, and gives a usage directive. Every word earns its place with zero redundancy.

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 simplicity (no parameters, no output schema), the description fully covers its purpose, output, and context. The usage note about creating/modifying events provides the needed situational context, making the tool complete for an agent to select and invoke correctly.

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 schema fully covers any inputs (none). The description adds no parameter details, but none are needed. The baseline for 0 params is 4, and the description's mention of listing names and writable status already implies what is returned.

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 local Calendar.app calendar names') and the output detail ('whether each calendar is writable'). It also connects to sibling tools by indicating it is a precursor to creating or modifying events when the calendar name is unknown, distinguishing it from event-related tools.

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 an explicit usage condition: 'Use this before creating or modifying events when the exact calendar name is unknown.' This clearly tells the agent when to invoke this tool and implicitly when not (when the calendar name is known). It gives actionable context without naming alternatives, which is sufficient for the simple use case.

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