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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds one genuinely useful behavioral fact — queries go through public resolvers, so cached/non-authoritative answers are possible — but says nothing about failure behavior for nonexistent domains or about TTL/answer structure.

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?

A single well-formed sentence with the action, the constraint, and the resolver context front-loaded; no filler or redundant clauses.

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 two-parameter read-only lookup with full annotation coverage, the definition is essentially sufficient. The only gap is that, with no output schema, it doesn't indicate what an answer looks like (record values, TTL) or what happens when the domain has no records of the requested type.

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%, so both parameters are already documented and the enum is fully constrained in the schema. The description restates the enum values and reinforces the one-type-per-call constraint, which is mildly useful but largely duplicates structured data.

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 and resource ('Look up DNS records') with an explicit scope: one record type from a listed enum, for a domain, via public resolvers. The 'one type' and 'public resolvers' qualifiers meaningfully separate it from specialized siblings like mx_lookup or dns_propagation_check, though it never names an alternative.

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?

Usage is implied rather than stated: the mention of public resolvers hints this is a point-in-time resolution query rather than a propagation or report tool, but there is no explicit when-to-use, when-not-to-use, or alternative named. An agent must infer the routing from sibling names.

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