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

No annotations are provided, so the description carries the full behavioral burden. It discloses that results are read-only lookups returning hostnames with priorities, but says nothing about failure modes (domain with no MX records), latency, caching, or whether this requires any auth or quota.

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?

Two short sentences, front-loaded with the operation and immediately followed by purpose; nothing is redundant. The parenthetical clarifying the record payload is efficient rather than wasteful.

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 single-parameter, annotation-free lookup with no output schema, the description covers what the tool does, what it returns, and why you'd use it. The remaining gap is the empty-result or error case, which is a minor omission rather than a blocking one.

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 already documented as a domain name 'no scheme'. The description adds no syntax or format detail beyond the schema, so the baseline of 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 precise verb (List) plus a specific resource (MX records for a domain) and even outlines the returned fields (mail server hostnames + priorities). That makes it clearly separable from generic siblings such as check_dns or check_dkim, even though those are not named.

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?

'Useful for verifying email delivery setup and detecting MX outages' supplies a usage context, but there is no explicit when-not guidance and no routing to alternatives like check_dns for full record sets or check_dkim for mail authentication. The agent must infer which tool to pick.

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