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

Annotations already declare readOnlyHint/idempotentHint, so safety is covered. The description adds genuinely useful behavioral context beyond that: cursor-based pagination via next_cursor, the exact record shape, and a licensing/attribution requirement for displayed data.

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 purpose, then pagination, then fields, then license. The field enumeration is long but each entry carries a type and definition that would otherwise be unavailable (no output schema), so the density is justified.

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 usefully compensates by defining every returned field and the pagination contract, plus the licensing obligation. It is complete for a read-only stats endpoint, though it never explains the filtering semantics (equals/starts-with, zone applicability) that the schema implies.

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 all seven parameters (tld, tld_in, operator, operator_prefix, domains_gte, limit, cursor) are documented in the schema. The description's 'next_cursor' note reinforces the cursor parameter but the field list it enumerates describes outputs, not inputs, so it adds little parameter meaning beyond the schema 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 resource ('name server operators and market share') with an implicit verb of returning aggregate statistics, which is enough to distinguish it from stats_dnssec and domain_lookup. It is clear but does not explicitly contrast itself with those siblings.

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?

No when-to-use guidance, no exclusions, and no named alternatives despite many adjacent siblings (stats_dnssec, domain_lookup, domains_*). The only procedural instruction is how to paginate, not when this tool is the right choice.

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