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

With no annotations, the description carries the full behavioral burden. It discloses two useful traits — the result is "live" (real-time, not cached) and a phone verification prerequisite gates the call — but says nothing about external side effects, rate limits, or what an unavailable yacht returns.

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, zero padding, with the core action front-loaded and the prerequisite following. Every clause carries actionable information.

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 three-parameter read tool with full schema coverage this is nearly adequate, but with no annotations and no output schema the agent still cannot tell what an availability response contains (boolean? pricing? alternatives?). One clause on the return shape would close the gap.

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?

Schema coverage is 100%, so id, from, and until are already fully documented including the YYYY-MM-DD format. The description only adds the framing that id refers to a single yacht over a date range, which is marginal beyond the schema.

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?

Uses a specific verb+resource ("check live availability of one yacht") bounded by a date range, which clearly separates it from list-style siblings like search_yachts. It does not explicitly name which sibling to use first, so it falls short of full sibling differentiation.

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?

"Requires a verified phone number" is a real prerequisite that implicitly routes the agent through verify_phone/confirm_phone before calling this. There is no explicit when-not guidance or named alternative for the case where the user has not verified a phone.

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