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

Annotations already cover the safety profile (readOnly, idempotent, openWorld), so the description is not obligated to restate them. It adds real behavioral context beyond that: the 10-name cap, the two lookup stages (DNS + RDAP), the default extension set, and the fact that available domains return a registration link and indicative price. It does not mention rate limits or failure behavior for malformed labels.

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?

Purpose, mechanism, and defaults are front-loaded, which is good. However, enumerating all 32 supported extensions duplicates the input schema's enum verbatim and consumes roughly half the description without adding information the agent cannot already see.

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?

There is no output schema, so the description carries the return-value burden and does so partially, explaining that available names return a registration link and price. It omits how unavailable names are reported and any batch/pagination behavior, but for a two-parameter lookup tool this is close to sufficient.

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?

With 50% schema coverage, the description compensates well: it names the eight default TLDs, where the schema only says 'default: main ones', and restates the 10-name ceiling and no-dot label convention. The full 32-entry supported list is useful because the enum is not self-explanatory about defaults, though it does repeat the schema.

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 gives a specific verb and resource ('Checks domain name availability'), states the mechanism (DNS + RDAP registry lookup) and the batch limit (up to 10 names). It is clearly distinct from suggest_names, though it does not explicitly contrast itself with check_name, which is the nearest sibling.

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?

'Ideal to compare several name ideas quickly' is a soft benefit statement rather than a usage rule; it implies when the tool shines but gives no exclusions and never routes the agent to check_name or suggest_names. Adequate but leaves the sibling choice to inference.

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