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

Explains the side effect that justifies readOnlyHint=false: it scans once only if no report exists, otherwise it is a pure read. Adds caching/staleness semantics via scanned_at, which the annotations cannot convey, and describes what the returned report contains.

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-loads the usage rule, but the single paragraph is repetitive: 'cheap first look'/'cheap read'/'right default for a first look' restate the same point, and the scan_domain preference is stated twice. It could be tightened without losing content.

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?

Given an output schema exists, the description still usefully notes the report contents and scanned_at for staleness. With one simple parameter, annotations, and the explicit scan_domain comparison, an agent has everything needed 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?

The schema already fully documents the single domain parameter (bare name, subdomain, unicode to punycode), so the description need not add syntax. It says nothing extra about the parameter, making the baseline 3 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 verb and resource (return the stored report for a domain) and explicitly contrasts it with scan_domain. An agent can immediately tell it is the cached-read sibling of scan_domain.

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 an explicit decision rule: use this when a recent report is enough, use scan_domain when state must be re-read now, with a concrete example (after a DNS change). Names the alternative and the condition that selects it.

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