Check a domain

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

Annotations already declare readOnlyHint, openWorldHint and idempotentHint, so the safety profile is covered. The description adds genuinely useful context by naming the data sources (registry via RDAP or WHOIS) and listing the checks, but says nothing about rate limits, failure modes for unregistered domains, or partial-result behavior — relevant given openWorldHint means external network dependence.

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 sentences, zero waste. The core purpose and scope come first, and the optional-flag guidance follows in a single subordinate clause.

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?

An output schema exists, so return values need no explanation, and annotations carry the safety profile. The description plus schema cover inputs adequately; only external-call behavior (rate limits, registry fallback failures) is unaddressed, which is a minor gap for this tool class.

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 description coverage is 100%, so all three parameters are already documented; the baseline of 3 applies. The description expands insights slightly (MX/SPF/DMARC specifics) beyond the schema's generic "email setup", but says nothing about include_raw_whois or its size implications.

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 ("Checks one domain name") and enumerates the checks performed: registration status via RDAP/WHOIS, expiry, registrar, DNS and reachability. The word "one" implicitly separates it from the bulk sibling check_domains.

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 a clear condition for the optional flag ("Set insights=true for nameservers, email setup ... and an HTTPS/TLS check"), which is real usage guidance. However, it never names the alternatives — check_domains, check_name_across_tlds, suggest_domains — so the agent must infer the single-vs-bulk split from the wording alone.

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