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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and non-destructive, so safety is covered; the description adds real value on top with 'from public records only', 'each line shows its evidence', and 'no sign-in'. Coverage is good, though it says nothing about latency, lookup failures, or partial results for unregistered domains.

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 core answer, then the evidence/scope caveat, then usage cases. The long enumerated clause is dense but each item is functional rather than filler; slightly heavy for a one-parameter lookup.

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?

No output schema exists, and the description compensates by itemizing the returned facets and noting that each line carries its evidence. An agent knows both inputs and expected output shape well enough to call it correctly.

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?

Single parameter with 100% schema description coverage, so the schema already carries the semantics; the description adds no format or edge-case guidance (e.g. subdomains, IDN, bare vs. www) beyond what the schema states. Baseline 3 is appropriate.

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 resource ('which companies a domain depends on') and enumerates the exact dimensions resolved: registrar/RDAP, DNS host, website host, MX, SPF/DKIM/bounce, DMARC. That granularity clearly separates it from siblings like check_domain or check_renewals, which cover only one of those facets.

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?

Gives concrete triggers: handoffs ('which accounts do I open when it breaks?'), before moving hosts, and setup audits. It does not, however, position itself against the closest siblings (check_domain, compare_email_hosting), so the agent must infer when a narrower tool is preferable.

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