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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful semantics beyond that: the three verdict outcomes, the reasoning that a PTR alone proves nothing, and the operational note that only the IP's controller can fix it. It omits rate limits or lookup-timeout behavior, which is the only gap.

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?

Front-loads the trigger sentence, then adds supporting semantics. Every clause carries real information (verdict meanings, the PTR-vs-FCrDNS distinction, who owns the fix), though the four-sentence block is denser than strictly necessary for a one-parameter read tool.

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, so return structure is covered elsewhere, and the description fills in the interpretive layer an agent needs — what each verdict means and how to communicate the result. For a single-parameter, read-only tool this is fully complete.

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 schema already documents that the IP must be public and that private/loopback/CGNAT are refused. The description's "Pass a public IPv4 or IPv6 address" largely restates that, so baseline 3 applies — adequate but not additive over the schema.

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 — reads the IP's PTR record, then resolves the hostname back to confirm it matches. It also names the exact domain concept (FCrDNS), which no sibling tool in the list addresses, so an agent can route here without ambiguity.

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?

Opens with a clear trigger ("Use this when the user asks about reverse DNS, PTR records, or FCrDNS for a mail server IP") and warns against a common misuse (never report a bare PTR as verified). It does not name a specific sibling alternative or an explicit when-not-to-use case, so it stops just short of a 5.

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