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

There are no annotations and the description discloses no behavior at all. It does not mention that the tool performs a network DNS query, what records are returned, whether it can fail, or any side effects.

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 text is short but this is under-specification, not effective conciseness. The redundant phrase 'Mx Lookup: Mx Lookup' adds no information and wastes the only opportunity to clarify the tool's behavior.

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 annotations, no output schema, and only a tautological description, an agent has insufficient information to reliably select or invoke this tool. The ambiguous 'input' parameter alone makes correct invocation uncertain.

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 the baseline is 3 even without description-level parameter details. The schema descriptions are generic ('Input to process', 'Domain to process'), and the description itself adds no clarification about which parameter is required or how they relate to an MX lookup.

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 is "Mx Lookup: Mx Lookup," which merely restates the tool name and title. It does not state a specific action, resource, or what an MX lookup actually does, so an agent cannot distinguish it from the many DNS-related 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?

No guidance is provided about when to use this tool versus alternatives like x402-dns-lookup, x402-ns-lookup, or x402-cname-lookup. The description gives no context, exclusions, or selection criteria.

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