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

Annotations only cover readOnly and openWorld; the description adds the failure contract (null price fields plus price_unavailable_reason when the currency is unavailable), the no-conversion rule, and a data-boundary guarantee that upstream cost prices are never exposed. That is real behavioral disclosure beyond structured fields, though rate limiting or freshness caching is not addressed.

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?

Four tight sentences, front-loaded with what the tool does, then return values, then currency behavior, then the privacy boundary. No filler and no repetition of schema fields.

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?

For a two-parameter read-only pricing lookup with an output schema, the description covers the essentials an agent needs: what is returned, currency defaults and limits, null-failure semantics, and the premium flag's purpose. Nothing critical 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 0%, so the description carries the load: it identifies the domain as a single-domain lookup and explains currency semantics, including the valid explicit values USD and EUR, which the schema does not enumerate. It compensates well for the schema gap without documenting format for the domain argument itself.

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?

The description opens with a specific verb and resource ("Get a fresh price quote for one domain") and enumerates exactly what is returned (registration, renewal, transfer prices, is_premium). This clearly separates it from siblings like check_domain_availability, register_domain, and renew_domain.

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?

The currency guidance (omit for default, USD/EUR explicit) gives usable calling context, but there is no explicit statement of when to call this versus siblings such as check_domain_availability or register_domain. The relationship to the purchase flow is left implied.

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