email_check_ptr

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It transparently details the internal resolution chain (MX -> IP -> PTR -> forward A), verifies IP matching, and states exactly what is flagged (missing PTR, FCrDNS mismatches). It does not mention edge cases like absent MX records or multiple MX hosts, resulting in a minor 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?

The description is two sentences long, front-loaded with the core purpose, then supported by the detailed resolution method and the practical consequence. Every sentence provides value and there is no redundancy or filler.

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?

Given the tool's simplicity (one parameter, no output schema), the description is highly complete. It explains the purpose, the step-by-step methodology, the verification logic, and the failure scenario, leaving little ambiguity about what the tool does and why an agent would invoke it.

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 coverage is 100%, so baseline is 3. The description adds meaning by clarifying that the 'domain' parameter is used to resolve its MX hosts first, not just the domain itself. This is a useful semantic addition beyond the schema's generic 'domain to check' phrasing.

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 a specific verb ('Check'), the resource ('PTR and FCrDNS for a domain's MX hosts'), and the exact verification logic (MX -> IP -> PTR -> forward A). This distinguishes it from sibling tools like email_check_spf or dns_reverse by focusing specifically on MX host reverse DNS validation.

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 the use case by noting that missing PTR records and FCrDNS mismatches 'can cause mail delivery failures', giving clear context for when this tool is relevant. However, it does not explicitly name alternatives or provide exclusion criteria, so it stops short of a full 5.

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