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

Annotations already declare readOnly, idempotent, non-destructive and open-world behavior. The description adds genuinely useful context beyond them: the tool builds a destination rather than fetching it, and NameBright and AWS Route 53 require an explicit copy/paste fallback rather than a direct redirect.

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?

Three tight sentences, no filler, with the core action front-loaded and the scope limits immediately following. Every sentence adds distinct information (action, exclusions, special-case fallback).

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?

With no output schema, the description still conveys that the result is a link/destination, though it never states the actual return shape (URL string vs. object) or what the copy/paste fallback yields. Coverage of the tool's behavior is solid for a low-complexity, 3-param read-only tool.

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 description coverage is 100%, so the schema already documents tld, name and registrar in detail, including the registrar-ID dependency on the registrars endpoint. The description only loosely gestures at 'name and extension', so the baseline 3 applies since the schema carries the load.

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?

States a specific verb and resource: 'Construct a verified registrar search destination for a proposed name and extension.' The description then explicitly disambiguates from adjacent capabilities ('Does not navigate, check availability, or purchase'), which separates it from check_availability and purchase-oriented siblings.

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?

Explicit negative guidance tells the agent when NOT to use it (not for availability checks or navigation), which steers it toward check_availability instead. However, it never names the alternative tool or clarifies its relationship to get_registrars, whose IDs the registrar parameter depends on.

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