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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=false), and the description adds substantive computation semantics: total cost components (first-year registration + renewals + WHOIS privacy), the 1-5 year horizon, and pre-tax USD normalization. It says nothing about result ordering, pagination, or how many registrars are returned by default, but the added cost model is real value.

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 sentences, both carrying load: the first defines scope, cost model, and unit; the second front-loads the negative constraint that prevents a wrong invocation. No 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 should carry return-shape burden; it implies a ranked registrar list via 'compare' and the limit parameter but never states what a result entry contains. Otherwise complete for a read-only, three-parameter lookup with full schema coverage.

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% — each parameter already documents its format, range, and default (tld without dot, limit ≤30 default 10, years 1-5 default 5). The description reinforces the single-extension scope and the meaning of the year horizon, but adds no parameter-level syntax or constraints beyond the schema, so the baseline of 3 applies.

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 (compare domain registrars) scoped to one extension and a defined cost basis. This is clearly distinguishable from the generic sibling compare_providers and from get_provider/find_vps without opening any 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 an explicit exclusion — 'This does not check whether a name is available' — which prevents a common misuse, and implies the context (pricing research for a chosen TLD). It stops short of naming an alternative tool for availability checks or for multi-extension comparisons.

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