list_calendars

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

With no annotations, the description must disclose behavior. It states the operation is a listing operation with the attributes returned, which is transparent. It does not claim any side effects, and 'list' implies a read-only operation. However, it doesn't mention whether authentication is required or if pagination applies, but for a simple zero-parameter list this is sufficient.

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 sentence with no redundant words. It front-loads 'List all calendars' and appends the key attributes, making it efficient and well-structured.

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?

The tool is simple with no parameters and no output schema. The description explains what the tool does and what information is returned (names, colors, visibility status), which is adequate for an agent to select and invoke it. It doesn't specify the exact response format, but that's not critical for a list operation.

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 the schema has no properties, so the description doesn't need to explain parameters. The mention of names, colors, and visibility status gives a hint about the response shape, which is useful. Baseline for zero parameters is 4.

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 uses the specific verb 'List' with resource 'calendars' and specifies the account scope ('Fastmail account'), along with the returned attributes (names, colors, visibility status). This clearly differentiates it from sibling tools like get_calendar_events, which operate on events rather than calendar metadata.

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 makes the use case clear: it's for retrieving calendar metadata. However, it doesn't explicitly name alternatives or exclusions (e.g., 'use get_calendar_events for events'), so the guidance is implied rather than explicit. Since the tool name and description are unambiguous, the context is clear even without explicit alternatives.

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