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

Annotations already declare readOnly, idempotent, open-world, non-destructive, so the safety profile is covered. The description adds genuinely non-derivable behavior: it reads public DNS only, cannot enumerate subdomains or unsupported record types, and enriches output with a named mail provider and source/as_of date. It stops short of noting rate limits or freshness guarantees.

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?

Front-loaded with the usage trigger, then parameters, then return shape, then limitations — a clean information hierarchy in four sentences with 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?

For a two-parameter lookup with an output schema present, the description covers trigger, argument set, enrichment behavior, and scope limits. Nothing an agent needs to select or invoke it correctly is missing.

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 both parameters are already documented in the schema, including the 'default: all' behavior for types. The description restates the supported enum values and the six-type cap but adds no syntax, normalization, or edge-case detail beyond the schema.

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+resource (look up DNS records) and enumerates the exact informational payloads: records, mail provider, and issuing certificate authorities. It is clearly distinguishable from sibling check_email_auth, which concerns authentication records rather than general DNS lookup.

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?

Opens with an explicit trigger condition and two concrete user-phrasing examples ("which mail provider does acme.io use?", "show the MX and CAA records for github.com"). It also states the negative boundary — cannot list subdomains or other record types — so the agent knows when to look elsewhere.

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