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

Annotations already declare read-only and idempotent, and the description adds substantial context beyond them: a batch cap of 10 extensions, USD currency with the ICANN fee included, the premium-pricing caveat that standard prices can understate a specific name's cost, and the tld_not_found failure mode. That is exactly the kind of surprise-prevention detail an agent needs before quoting a price.

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?

A single dense paragraph with the purpose front-loaded and the price/premium caveat placed where it matters. It is on the long side, but essentially every clause corresponds to a distinct returned field or a behavioral caveat, so little is wasted.

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?

Rich annotations and an output schema carry the structural load, and the description still supplies the operational knowledge an agent needs: batch limits, currency, premium-price escalation path, and the not-found outcome. Nothing required to call it correctly or interpret results is missing.

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 schema already explains the no-dot format, so baseline would be 3. The description earns a bump by restating the 10-per-call ceiling and illustrating expected inputs (.app, .dev, .us) in the context of what they imply about the returned data.

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 what OrbitFour charges and requires for domain extensions') and enumerates the returned data: prices, term lengths, WHOIS privacy, eligibility, https_required, and registration JSON Schemas. This is clearly distinguishable from the sibling tools, which operate on individual domains rather than the TLD-level ruleset.

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?

Provides a concrete routing rule: when premium_possible is true, the specific name must be quoted with check_domain, and unknown extensions return tld_not_found. It does not state when to prefer check_transfer or search_domains, but the split between TLD-level rules and domain-level checks is clear enough to act on.

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