check_function_availability

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

Annotations already declare readOnlyHint, destructiveHint, idempotentHint, and openWorldHint, which cover safety and idempotency. The description adds that it reports availability for the configured account and API token, giving extra context beyond annotations about scope. It does not contradict annotations.

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 three sentences, each earning its place: purpose, usage guidance, and exclusions. Front-loaded with the core action, no redundant words.

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 no input parameters and no output schema, the description provides sufficient context for a simple diagnostic tool. It explains when to use and what it does, though it does not describe the output format (e.g., list of function names or flags), which would be helpful for completeness. However, the low complexity justifies a 4.

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?

Input schema has zero parameters, so baseline is 4 per guidelines. The description does not need to add parameter information, as there are none to describe.

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 a specific verb 'report' and resource 'function availability', clearly distinguishing from sibling tools like list_emails or download_attachment. It states exactly what the tool does: reports which Fastmail functions are available for a given account and token.

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 provides 'when to use' scenarios: setup seems incomplete, a mail tool fails unexpectedly, or a quick capability summary is needed. It also clarifies 'when not to use' by stating not for reading email content or browsing inbox, providing clear context versus sibling tools.

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