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

Annotations only declare readOnlyHint=true, and the description goes well beyond that: it discloses the resolution mechanism (DNS-over-HTTPS via a public resolver), input flexibility (bare hostname or full URL), the breadth of what is fetched, and a per-call price of $0.003 USDC under x402. Cost and payment model are genuinely useful behavioral context an agent cannot get from annotations. It does not cover failure behavior for non-existent domains or latency, which keeps it short of a 5.

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?

The lead clause 'Full DNS profile of a domain in one call' is front-loaded and the rest is a compact enumeration, with the pricing note last as a secondary detail. It is dense but every clause carries information; a bulleted record list would scan slightly better than the long comma chain.

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 no output schema, the description has to describe return values itself, and it does so thoroughly, including derived fields like SPF policy, all-mechanism, reporting address and inferred providers. Input handling, resolver choice and cost are all covered. Only edge-case behavior (NXDOMAIN, timeouts) is absent, a minor gap for a read-only lookup tool.

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?

There is a single parameter with 100% schema description coverage, so the schema already explains that a domain or hostname is expected and that a URL is reduced to its host. The description's 'accepts bare hostnames or full URLs' restates that same fact without adding format rules, validation constraints, or examples. Baseline 3 is appropriate when the schema carries the semantics.

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 a specific resource (a domain's DNS profile) and enumerates exactly what is returned: A/AAAA/CNAME/MX/NS/TXT/SOA/CAA records, parsed SPF and DMARC, DNSSEC flag, and inferred hosting/email/web providers. That is far more specific than the bare name 'dns'. It never explicitly contrasts itself with the sibling 'domain' tool, so an agent must infer the boundary between the two.

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 implied by 'Full DNS profile ... in one call', which signals it should be used when a complete record set is needed rather than a single lookup. There is no explicit when-to-use/when-not statement and no named alternative among the siblings. An agent can guess the context but is given no routing rule.

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