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

No annotations are provided, so the description carries the full behavioral burden. It does add one genuinely useful non-schema fact — 'Cost: 1 credit per call' — which tells the agent this is a metered operation worth using deliberately. It does not disclose whether the lookup is read-only, how failures (NXDOMAIN, timeouts) are surfaced, or any rate limits, leaving meaningful gaps for an unannotated tool.

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 short sentences with zero filler. The functional scope is front-loaded and the cost constraint follows immediately. 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?

With no output schema and no annotations, the description should ideally describe the shape of the result, error behavior, and safe usage. It partially compensates by listing the record types returned, but omits any return-format or failure-mode detail for a tool whose structured metadata offers nothing.

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?

There is a single parameter, 'domain', and the schema description coverage is 0%, so the description must compensate. Saying 'a domain's ... records' implies the parameter is a domain name, but it adds no format guidance (e.g., whether a bare domain, subdomain, or URL is accepted) despite the schema imposing a pattern, minLength, and maxLength.

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 gives a specific verb ('look up') and resource ('a domain's ... records') and enumerates exactly which record types are returned (A, AAAA, MX, TXT, NS, CNAME), so an agent knows precisely what the tool does. It does not, however, distinguish itself from adjacent siblings such as domain_info, subdomain_enum, or reverse_dns, which also operate on domains.

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 choose this tool over domain_info, subdomain_enum, or reverse_dns, and no stated prerequisites or exclusions. The only usage-adjacent information is the cost line, which is not a selection criterion. The agent must infer applicability entirely from the tool name.

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