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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is fully covered. The description adds only that this is part of a domain audit; it does not discuss rate limits, caching (the force_refresh semantics live in the schema), or what a failure result means, so it contributes modest value beyond the structured fields.

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 tight sentences with the operation front-loaded and the audit-relationship context second. No filler, no restatement of the title.

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 values need not be described, and annotations cover the safety profile; the description is adequate for a single-domain read check. It stops short of noting what 'forward-confirmed' requires (forward A lookup matching the PTR name) or how results relate to the scan_domain findings, which would make it fully self-sufficient.

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% with all three parameters documented, including the format enum and the force_refresh cache-bypass rationale. The description adds no parameter-level information, so the baseline 3 applies.

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?

Uses a specific verb ('Verify') with a precise technical resource ('forward-confirmed reverse DNS (PTR/FCrDNS)') and scopes it to mail servers. An agent can distinguish this from check_mx or check_spf, though the description does not explicitly contrast against the many other DNS-record checking siblings.

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?

'Part of the scan_domain audit' implies this is a sub-check of the broader audit and signals the alternative (run scan_domain for the full sweep), but there is no explicit when-to-use/when-not guidance and no mention of prerequisites such as needing a resolvable MX/PTR record first.

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