Check Reverse DNS

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), but the description adds substantive interpretive context: the three verdict outcomes, the caveat that a bare PTR proves nothing because the IP operator controls its own reverse zone, and who actually owns the fix. This is exactly the kind of domain context structured fields cannot carry.

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-loaded with the trigger condition and organized so the mechanism, the verdict vocabulary, the caveat, and the ownership note each appear once. It is dense rather than padded, though the verdict enumeration and the 'never report a bare PTR as verified' warning could be tightened slightly.

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 carries the return-value burden and does so by defining confirmed, ptr_missing, and mismatch. Combined with the usage trigger and input constraint, an agent has everything needed to call and interpret this tool without ambiguity.

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 single parameter is fully documented there, including the refusal of private/loopback/CGNAT ranges. The description's 'Pass a public IPv4 or IPv6 address' restates the schema rather than extending it, 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?

States a specific verb and resource ('Check one sending IP's forward-confirmed reverse DNS (FCrDNS)') and spells out the mechanism (read PTR, resolve back, compare). It is clearly distinguishable from siblings like check_record or get_domain_records, and the opening sentence names the exact query types it serves.

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 opening sentence gives explicit trigger conditions ('when the user asks about reverse DNS, PTR records, or FCrDNS for a mail server IP') and the closing line constrains input to public addresses. It stops short of naming alternative sibling tools (e.g. check_record) for related-but-different questions, so it is clear but not fully routing.

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