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

Annotations only declare readOnlyHint, so the description carries most of the load and does it well: it discloses the default extension set, that only the lowest-priced listing is returned, that for-sale domains may lack a price, that listing type (buy now/offer/auction) is unknown, and that registration fees are excluded. It stops short of saying anything about rate limits or response shape, but the caveats are the ones that would actually mislead an agent.

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 the core action and output, then caveats, then sibling routing. A couple of clauses restate what the schema already documents (the default .com/.net/.org/.ai set), but no sentence is pure filler.

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 must explain return values and does: availability states, USD asking price, marketplace, and the lowest-listing-only rule. Combined with the sibling routing and caveats, an agent has everything needed to call it and interpret the result.

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; the description still adds value by tying the tlds default to user intent ('unless the user names other extensions, so mention any of those that are for sale'), which tells the agent how to act on results rather than just how to fill the field.

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 ('check whether a domain name is for sale and what it costs') and enumerates the availability states it returns. It explicitly distinguishes itself from the two closest siblings, get_domain_value and get_domain_info, by naming them.

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?

Gives concrete trigger phrasings ('is cova.com for sale?', 'price for cinch.com') and explicit exclusions routed to alternatives: appraisal goes to get_domain_value, ownership to get_domain_info. Nothing is left to inference.

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