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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the bar is lower. The description adds genuine behavioral context: comma-separated nameservers resolve to an AND/intersection rather than an OR, and that capability is gated to higher plans. No rate limits or result-size behavior are mentioned.

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?

Three short sentences, front-loaded with the core purpose before the intersection nuance and the sibling pointer. Efficient and free of filler, though the trailing 'Related: whois, dns.' is a thin addition rather than a routing instruction.

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 read-only lookup tool with rich annotations, a 100%-covered 11-parameter schema, and an output schema, the description supplies everything an agent needs to select and invoke it correctly. Return format and pagination are handled by the output schema and parameter docs respectively.

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%, so the baseline is 3. The description's explanation of intersection semantics largely restates what the 'ns' parameter description already says verbatim, and it says nothing about page, sort, or the length/character filters, so it does not meaningfully exceed 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?

States a specific verb and resource: 'find gTLD domains hosted on a specific nameserver', which is precisely the inverse of a forward DNS lookup and clearly distinct from sibling tools like dns and whois. The added scoping ('filtered by TLD and keyword') and the 'Related: whois, dns' pointer make the tool's identity immediately legible.

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 a concrete usage context (find domains on a nameserver) plus the multi-nameserver intersection pattern and the plan-tier caveat, which tells the agent when the feature is even available. It lacks explicit 'when not to use' guidance or a direct alternative to route to for forward lookups, keeping it out of the top band.

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