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

Annotations already declare readOnlyHint, openWorldHint, and destructiveHint=false, so the safety profile is covered. The description adds two genuine behavioral facts beyond that: a hard cap of 12 aliases and that loops are detected and reported. It does not mention error behavior (NXDOMAIN, SERVFAIL) or truncation reporting, keeping it from a 5.

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?

One sentence, front-loaded with the action and resource, then the two operational constraints. No filler or redundancy.

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 lookup tool with strong annotations, the description is nearly sufficient: it covers what is resolved, the depth limit, and loop handling. It leaves the parameter's accepted hostname format and the shape of the returned chain implicit, which is a minor but real gap.

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 0% for the single required parameter, so the schema only gives a name and length bounds. The description says 'hostname,' which slightly clarifies that a bare host should be supplied rather than a URL, but leaves format details (trailing dot, IDN, subdomain handling) unspecified.

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?

Specific verb (follow) and resource (CNAME chain for a hostname), with concrete scope details: max 12 aliases and loop reporting. It does not name or distinguish itself from any sibling (e.g., check_dns_propagation or check_domain_delegation), so it stops short of a 5.

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 only implied by the verb 'follow the CNAME chain' — an agent can infer it is for diagnosing alias resolution. There is no explicit when-to-use, when-not-to-use, or alternative tool named among the many DNS siblings.

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