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

With no annotations provided, the description carries the burden of disclosing behavior. It explicitly states 'Read-only' and 'price 0.0 (free)', which are important safety and cost traits. It also specifies the method (DNS-over-HTTPS). However, it does not describe the response format or potential failures (e.g., no PTR record), which would be useful but is not critical for such a simple read-only operation.

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?

The description is exceptionally concise, with two short sentences that deliver all necessary information: purpose, method, safety, and cost. No filler or redundant phrases. Every word earns its place.

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?

For a simple single-parameter tool, the description covers the core aspects: what it does, how it does it, and that it is safe and free. It does not describe the return structure, but the term 'hostname(s)' implies the output. Given no output schema and the low complexity, the description is nearly complete, leaving only minor gaps around response details.

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?

The input schema fully documents the only parameter 'ip' with description 'IPv4 or IPv6 address', so schema coverage is 100%. The description adds little beyond that, merely saying 'for an IP' which is redundant. It does not add syntax or format details beyond the schema, so the baseline score of 3 is appropriate.

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?

The description clearly states the tool's function: 'Resolve the reverse-DNS (PTR) hostname(s) for an IP'. The verb 'resolve' and the specific resource 'reverse-DNS (PTR) hostname(s)' make the purpose unambiguous. It also distinguishes itself from sibling tools like ip_reputation_asn_lookup or domain_intel_dns_lookup by explicitly focusing on PTR records.

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 implies usage for reverse DNS lookups but does not explicitly state when to use this tool over alternatives. It mentions 'via free DNS-over-HTTPS' and 'Read-only; price 0.0 (free)', providing some context, but no direct comparison to sibling tools or exclusions. The usage is implied, not explicit.

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