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

With no annotations, the description carries the full burden, and it does disclose the read-only nature plus the return ordering and that IPs are resolved. It omits failure behavior (no MX, NXDOMAIN), caching/rate limits, and whether resolution failures are reported, so the safety profile is only partially covered.

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?

A single front-loaded sentence stating the resource, the ordering, the enrichment, and the safety profile, with zero filler. Nothing could be removed without losing information.

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?

There is no output schema, so the description usefully explains the return shape (preference-ordered hosts with resolved IPs) and states read-only. For a simple one-parameter lookup this is nearly complete; only error/edge-case behavior is unaddressed.

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% for the single 'domain' parameter, so the schema already carries the semantics. The description adds no format or syntax detail beyond what the schema states, which is the expected baseline 3.

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 (List) and resource (MX records) and further specifies ordering by preference and IP resolution of each host. An agent can distinguish it from generic siblings like dns_lookup or spf_check without opening a schema.

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?

Usage is only implied by the resource itself (mail-routing investigation); there is no explicit when-to-use or when-not statement, and the obvious alternative, dns_lookup, is never mentioned. Adequate but leaves routing between siblings to inference.

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