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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered structurally. The description's real contribution is disclosing what comes back — summary, site title/description with date checked, pricing/free tier, agent-readiness signals, traffic and revenue with source and dates, referral code, and page link — which is genuinely useful given there is no output schema, though it says nothing about behavior on unknown domains or data freshness limits.

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 scope ("One tool by domain") followed by a dense but purposeful field inventory; every clause conveys a distinct returned attribute. The single run-on sentence with heavy comma nesting slightly hurts scannability but wastes nothing.

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, enumerating the returned fields is the description's main job, and it does so comprehensively, including provenance details like check dates and revenue sources. The remaining gap is the absence of any error or not-found behavior, which matters for a lookup keyed on an arbitrary domain.

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 the single domain parameter is fully documented in the schema, including format example and provenance. The description adds no further meaning about the parameter, 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?

"One tool by domain" states a specific resource (a single tool) and the keying dimension (domain), which clearly separates it from the sibling search_tools (plural listing). The verb is implicit rather than explicit, and the rest of the sentence is a return-field inventory rather than purpose elaboration, so it falls short of the crisper verb+resource framing.

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 only implied: the definition frames this as a single-record lookup keyed by domain, and the schema's "Domain from search_tools" hints at the search-then-get workflow. It never states when to prefer this over search_tools or compare_tools, nor any prerequisite such as a domain needing to already exist.

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