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

Annotations only declare readOnlyHint and openWorldHint; the description goes well beyond them by stating there are no purchase side effects ('never registers or buys'), giving per-mode credit costs, and specifying credits are 'charged only when a call succeeds' — exactly the billing behavior an agent needs before firing a paid call.

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?

Front-loaded with purpose, then modes, then the boundary, then the mode/field map, then cost — a sensible ordering for a six-mode tool. It is dense and long, but for an 11-parameter multi-mode tool nearly every clause carries decision-relevant information; only the enumerated return list is mildly redundant with the schema.

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?

No output schema exists, so the description carries the return burden and does so per mode ('name ideas with prices, extensions that fit with reasons, one name across extensions, availability...'). Combined with cost, side-effect, and mode/param guidance, an agent has everything needed to call this correctly.

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 the baseline is 3, but the description adds genuine cross-parameter semantics the schema cannot express: 'mode decides which fields apply: company_name and description for the suggest modes, query for search-extensions, domains for check-availability, tlds for pricing.' It stops short of covering offset, exact_extension, or the precedence rules already in 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?

Opens with a specific verb+resource ('Find domain names and the extensions that fit a business') and then enumerates what each of the six modes returns, so an agent can map intent to mode without opening the schema. It also explicitly demarcates itself from the sibling site-intel ('for facts about a domain that is already live').

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?

States the when ('to name a business or check domains before buying one'), the when-not ('it never registers or buys a domain'), and the alternative for the adjacent need (site-intel for live-domain facts). The mode-to-field mapping further tells the agent which mode to select for which job.

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