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

Annotations already state that this is a read-only, idempotent, non-destructive operation. The description adds real value beyond them: the response comes from a public resolver (Cloudflare, with Google as fallback) and reflects that resolver's cache, so a fresh zone edit is visible only after TTL, and NXDOMAIN means the name does not exist. The one gap is that it does not describe the response shape, but the freshness and error semantics are above the annotation baseline.

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 compact sentences, front-loaded with the most useful content (record types plus SPF and DMARC). There is no filler; the only minor weakness is that the opening is a bare list rather than a clear statement of the action.

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 tool with rich annotations, this covers record types, the SPF and DMARC check, resolver and cache behavior, and the NXDOMAIN case. Since there is no output schema, the one thing missing is a note on how results are returned such as grouping by record type or values only.

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%: the only parameter is documented, with an example (mail.example.ru). The description adds that the input is exactly one name, a domain or subdomain, which reinforces the single-name scope but adds little 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?

The description names the exact record types returned (A, AAAA, CNAME, MX, NS, TXT, SOA, CAA), so the tool's purpose is clear. It also adds the SPF/DMARC presence check, but never distinguishes this tool from check_domain or whois_domain, leaving the agent to infer the split.

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?

The description gives no guidance on when to use this tool rather than check_domain or whois_domain, and it states no preconditions or exclusions. The closest it comes is describing the behavior around NXDOMAIN and TTL, which is informational rather than routing guidance.

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