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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=true, and destructiveHint=false, so the safety profile is fully covered. The description's only added behavioral detail is that the API is free and public, which implies no auth is required but says nothing about rate limits or behavior on nonexistent domains.

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 tight sentences with zero filler, leading with the operation and its scope. Nothing is wasted or buried.

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 and annotations carry the safety profile, so the description need not explain return values or side effects. It is adequate for a simple read-only lookup, though it leaves the sibling-selection question unanswered.

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%, and the 'type' parameter even has an enum, so the schema fully documents both inputs. The description's type list in parentheses merely echoes the enum values rather than adding format or semantic detail, so 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?

States a specific verb ('look up') and resource ('DNS records') and enumerates the record types covered, so the scope is unambiguous. However, it does not distinguish itself from siblings like tools_cname_lookup, tools_txt_record_lookup, or tools_spf_record_checker, which overlap in scope.

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?

There is no guidance on when to use this tool versus the numerous specialized siblings; the description only notes it is a 'Free public API.' An agent must guess whether this general lookup or a targeted sibling (e.g. tools_txt_record_lookup) is preferred.

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