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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds real side-effect disclosure beyond them: it contacts only public DNS and the EHLO answer of at most 2 mail servers, sends no mail, and never registers or claims a name to test takeover. Those are exactly the questions an agent needs answered before running an open-world probe.

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 trigger and examples, then inputs, returns, and safety in a logical order with no filler. It is dense and long-winded in the return-value clause (enumerating all four checks in detail despite an output schema), which is the only real redundancy.

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?

With an output schema present, the description need not explain structure, yet it still previews the shape (per-check status, faults ordered worst-first, source and as_of) and discloses the probing limits. Nothing material for correct invocation 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 coverage is 100% and the schema itself explains normalization of web/email addresses into a domain. The description contributes only 'Pass the domain', adding no syntax or edge-case meaning beyond the structured field, so the baseline 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?

Names a specific verb and resource (DNS security hygiene checks) and enumerates exactly what is inspected: CAA, DNSSEC, STARTTLS, dangling CNAMEs. That inventory clearly separates it from check_dns_records (generic records) and check_email_auth (SPF/DKIM/DMARC) without needing to open either 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?

Opens with an explicit trigger condition plus two concrete user-question examples, so an agent can pattern-match intent reliably. It stops short of naming sibling tools or stating when not to use it (e.g., plain record lookups belong to check_dns_records), so routing against alternatives is inferred rather than stated.

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