check_mx

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

Annotations already declare readOnly, idempotent and openWorld, so the safety profile is covered. The description adds genuinely new behavioral context — that results identify the hosting provider and that this is a component of the scan_domain audit — which an agent cannot get from the annotations or schema.

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 tight sentences: purpose, enrichment detail, then usage trigger. Front-loaded and no 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?

Output schema exists so return values need no explanation; annotations cover safety; all three parameters are documented in the schema. The description supplies the remaining context an agent needs — what the data means and where it fits in the broader audit.

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%, so domain, format and force_refresh are all documented at the schema level. The description adds no guidance on when to pick compact vs full output or when a refresh is warranted, so it stays at the baseline.

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 ("Look up MX records for a domain") and immediately elaborates what that reveals: inbound mail servers and hosting provider (Google Workspace, Microsoft 365, Proofpoint). That provider-inference framing separates it from generic DNS siblings like check_ns or check_txt_hygiene.

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?

Gives an explicit triggering question ("Use when asked which email provider hosts inbound mail") plus a secondary use case (inspect MX configuration). It does not exclude the adjacent check_mx_reputation sibling, so an agent facing a mail-hygiene question has to infer which to call first.

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