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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is fully covered by structured data. The description's added value is the result shape (totals, per-TLD counts) and the co-registration intent, but it says nothing about matching semantics (exact vs. substring on the nameserver) or result limits.

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?

Two sentences, zero redundancy: the first states the output, the second states the intent. Front-loaded with what the agent gets back, which is the most decision-relevant information.

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?

An output schema exists, so return values need not be re-explained, and annotations cover the safety profile. For a single-parameter read tool the description is nearly sufficient; the only real gap is match semantics for the nameserver argument.

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?

One parameter at 0% schema description coverage, so the description must carry the load. The field name "nameserver" plus the phrase "that use a given nameserver" confirms the semantic meaning, but no format is given (hostname, trailing dot, case sensitivity, wildcard support), so an agent could still supply a malformed value.

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?

Specific verb (list) + resource (scanned domains) + filter (using a given nameserver) + stated return shape (totals and counts per TLD). An agent can tell what it does immediately. It does not, however, differentiate itself from the near-identical sibling search_by_registrar, which is the closest sibling in the search_by_* family.

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?

"Useful for finding domains registered together" gives a genuine use case and implies when an agent would reach for this tool. But it names no alternative and gives no when-not guidance (e.g., prefer search_by_registrar for registrant-org pivots), so the sibling selection is left to inference.

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