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

Goes well past the annotations (readOnly/idempotent) by disclosing what the tool does NOT do ('Does not register, reserve or charge'), that it works unauthenticated, and how results are classified: Unavailable, For sale by another party, premium as distinct from a marketplace listing, plus a trademark note caveat that is 'not legal advice'.

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 return in the first sentence, with the operational rules following. It is several sentences long, but nearly every one carries distinct information (pricing, availability states, trademark caveat); the bare-name rule is stated twice across description and schema, a minor redundancy.

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 carries the full burden of explaining return values, and it does so explicitly (available/cost, Unavailable, For sale, premium, trademark note). Combined with the read-only and no-account statements, an agent has everything needed to call and interpret this tool.

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 single parameter is fully documented in the schema, including the .com/.nl/.app expansion that the description also repeats. The description adds no syntax, normalization, or invalid-input guidance beyond the schema, so this sits at the baseline.

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 ('Checks one domain name with the domain registry') and the exact return payload ('whether it is available and what it costs'). It further distinguishes scope with 'One name per call' and explains the bare-name multi-TLD behavior, which no sibling tool offers.

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 operating context: 'One name per call', 'Works without an account', and an explicit downstream instruction: 'When the exact name is taken, offer the human the free variant names.' It does not, however, name the alternative sibling (e.g. connect_domain for registration, check_trademark for marks), so routing is implied rather than stated.

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