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

With no annotations, the description carries the full burden and does well: it declares the read-only nature, states it reads the passive-DNS database and never touches the target, and notes the keyless data source. It still omits operational traits such as rate limits, pagination, or result caps, so it is strong but not exhaustive.

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 dense sentences, front-loaded with the core purpose and scope before the differentiator and safety note. Every clause carries information; nothing is redundant with the schema or title.

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 one-parameter, no-output-schema tool, the description covers source, directionality of results, per-record fields (first/last-seen, observation count), and read-only safety. It is nearly complete, missing only result-volume/pagination behavior.

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 coverage is 100% with a single documented 'query' parameter, so the baseline is 3. The description adds real semantic value by explaining that a domain yields historical answers while an IP yields the names that pointed at it, clarifying how the one input changes the result shape.

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+resource: historical DNS resolutions for a domain or IP, with the exact data source (Mnemonic keyless Passive DNS) named. It clearly distinguishes itself from live-lookup siblings like dns_lookup and reverse_dns by describing bidirectional historical mapping (answers for a name, names for an IP).

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?

'Surfaces old/rotated infrastructure a live lookup can't' gives clear usage context and implicitly routes the agent away from live-DNS siblings. It stops short of explicitly naming the alternative tools or stating exclusions, so it is clear context but not full when/when-not guidance.

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