Check domain availability

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

Annotations already cover read-only, idempotent, open-world and non-destructive behavior, so the bar is lower; the description adds real value by naming the RDAP provider and, importantly, disclosing that a 404 result is explicitly non-authoritative and not a purchase guarantee. That caveat is exactly the kind of behavioral context annotations cannot express, though rate limits or provider failure behavior are not addressed.

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 tightly written sentences, front-loaded with the action and scope, followed by the result-interpretation rule. No filler or repetition of the title.

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 carries the burden of explaining return semantics, and it does so precisely: found record means registered, 404 suggests availability. The non-authoritative caveat closes the main interpretive gap for an agent reporting results to a user.

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% and the single 'domain' parameter is fully documented with an example in the schema, so the schema does the heavy lifting. The description reinforces the 'fully qualified domain' expectation but adds no format, normalization, or edge-case detail beyond it.

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 gives a specific verb and resource (check a domain's availability) and scopes it to 'one fully qualified domain,' which implicitly contrasts with the plural/variant siblings like search_tld_variants and list_tlds. It stops short of naming an alternative or exclusion, so sibling differentiation is inferred rather than stated.

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?

It conveys that this is for a single FQDN and explains how to read the result (record = registered, 404 = likely available), which implies the use case. However, there is no explicit when-to-use vs. when-not guidance and no routing to siblings such as compare_registrars or search_tld_variants for related needs.

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