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 covered. The description earns credit beyond that by disclosing what the call actually inspects and reports (key type, RSA key length, weak/revoked flagging) and that the no-selector path fans out across common selectors, which implies extra queries and latency.

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?

Three short sentences, front-loaded with the purpose and then the mode behavior and reporting details; nothing is filler. Minor redundancy with the schema's selector note keeps it just short of ideal.

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, the description usefully sketches what the result contains (key type, key length, weak/revoked flagging), which is the right compensation. However, the selector required-vs-optional ambiguity and the absence of any note on how multiple common-selector results are returned leave real gaps for a network-facing lookup tool.

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 description's selector behavior largely restates the schema's "optional, blank = try common ones" note. Worse, it calls selector optional while the schema lists it under required, leaving the agent unsure whether the argument can be omitted — a conflict the description does nothing to resolve.

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?

"Check DKIM public keys for a domain" gives a concrete verb and resource, and the DKIM resource itself separates it from sibling record checks such as dmarc_check, spf_lookup, and bimi_check. The follow-up clauses add scope (selector vs. common-selector sweep) and what is inspected (key type, RSA length, weak/revoked flags), so an agent knows exactly what this tool answers.

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?

The description explains the two modes (with a selector vs. without one), which is genuine invocation guidance. It never states when to choose this over related checks like dmarc_check or domain_health_report, nor any prerequisites or exclusions, so usage is implied rather than prescribed.

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