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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety and external-network profile is covered structurally. The description adds that the source is public RDAP data and lists the fields returned, but says nothing about rate limits, behavior for unregistered or malformed domains, or latency.

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?

Two tight sentences with the action and returned data front-loaded, followed by a single sentence of usage context. Nothing is redundant or padded.

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 one-parameter read-only lookup with no output schema, the description does the job: it names the data source and summarizes the return fields, reducing the need for an output schema. It stops short of covering failure modes (domain not found, RDAP lookup errors) which would complete it.

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 required parameter with 100% schema description coverage and an inline example (example.com). The description adds no format constraints (TLD handling, IDN, subdomain acceptance) beyond what the schema already supplies, 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?

States a specific verb and resource ("Look up a domain's public registration data (RDAP)") and enumerates what it returns: registration status, registrar, key dates. It does not explicitly distinguish itself from close siblings like check_subdomain or get_custom_domain, which keeps it below a 5.

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?

"Useful before suggesting a custom domain" implies a usage scenario, but there is no explicit when-not guidance and no named alternative among the several domain-related siblings (check_subdomain, get_custom_domain, set_custom_domain). The agent must infer which domain tool fits.

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