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

Annotations already cover the safety profile (readOnly, idempotent, openWorld, non-destructive), so the bar is lower. The description adds genuinely new behavioral context beyond them: the data comes from a third-party source (HackerTarget) and the result is a list of other domains on the same DNS server. It omits freshness/rate-limit caveats that typically apply to third-party reconnaissance 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?

Two sentences, front-loaded with the query intent an agent is most likely to match, followed by mechanism and use cases. No filler or repetition of the title, and every clause earns its place.

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 single-parameter read-only pivot tool with no output schema, the description covers the input form and characterizes the return (other domains served by the same nameserver). It stops short of noting result limits, possible empty results, or truncation, which an agent would benefit from knowing.

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 with 100% schema description coverage, so the schema already documents both accepted forms (nameserver hostname or a domain whose nameservers to pivot on). The description adds no further parameter guidance such as accepted formats or normalization behavior, so the baseline 3 applies.

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 states a specific operation — finding other domains served by the same nameserver — with verb, resource, and the pivot direction (from nameserver/hostname back to domains). It leads with user-phrasing synonyms ('What else uses this nameserver', 'domains sharing DNS with [X]') and names the underlying technique (shared-nameserver search), which cleanly separates it from siblings like dns_lookup, reverse_dns, or whois.

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?

It names two concrete scenarios for use: mapping an operator's infrastructure footprint, and assessing blast radius if a nameserver goes down. That is clear when-to-use context, but it never states when NOT to use it or points to a sibling (e.g. dns_host_search or dns_lookup) for simple record lookups.

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