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

Annotations already declare readOnlyHint, openWorldHint, and destructiveHint=false, so safety is covered. The description adds genuinely new behavioral context beyond the annotations: the per-call cost of 10 credits and the fact that multiple matching hostnames may be returned. It does not say what happens when no PTR record exists (empty result vs. error), which is the remaining 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?

Three short sentences, front-loaded with the purpose and cost placed at the end where it is easy to scan. The only waste is the redundant 'Reverse DNS Lookup: Reverse DNS Lookup' restatement of the tool name.

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-value shape need not be explained. For a single-parameter, read-only lookup, the description covers the mechanism (PTR), address families, result multiplicity, and cost — everything an agent needs to decide and invoke correctly.

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 already documents 'IPv4 or IPv6' with an example. The description restates the same constraint ('resolves IPv4 and IPv6 addresses', 'Pass any IP address') without adding format or validation detail, so the schema is doing the work.

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: resolves IPv4/IPv6 addresses into hostnames via PTR records. The word 'reverse' plus the PTR mechanism clearly distinguishes it from forward-resolution siblings like DNSLookup and from IPLookup, though it never names those alternatives explicitly.

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 implied by the description ('Pass any IP address to check if reverse records exist'), which gives an agent enough to know the input, but there is no explicit when-to-use vs when-not guidance relative to DNSLookup, IPLookup, or WHOISLookup, all of which appear in the sibling list.

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