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

Annotations already declare read-only, idempotent, open-world, non-destructive, and the description reinforces with 'read-only' and 'Up to 10 names per call.' It adds genuine behavioral context beyond annotations: that a malformed name or unsold extension returns an error field rather than failing, and that a null 'available' means the registry could not be asked rather than the name being taken.

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?

The purpose is well front-loaded, but the bulk of the description is a field-by-field explanation of return values (first_term, pricing_source, purchasable, purchase_blocker, pricing_sources) for a tool that has an output schema. That material is largely redundant against structured data and dilutes the routing guidance the agent actually needs.

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?

Given a two-parameter, read-only lookup with a full output schema, the description covers the essentials: scope, batch limit, the exact-vs-search distinction, and error behavior for malformed names. The only omission is any mention of the transfer and TLD-requirements siblings.

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 schema already documents both parameters including the max-10 limit. The description only restates the 10-name cap and adds no syntax or format detail for 'years' beyond what the schema provides. Baseline 3 applies when the schema does the heavy lifting.

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 — 'Look up exact domain names: whether each can be registered now, and its per-year registration, renewal and transfer price' — and explicitly contrasts with the sibling search_domains ('confirm a search_domains suggestion'). An agent can route between the two without opening either schema.

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 clear usage context: 'Use it for names you already have and to confirm a search_domains suggestion,' naming the alternative and the condition that selects it. It does not address the other siblings (check_transfer, get_tld_requirements) or state when-not, so it falls short of a 5.

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