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

Discloses behavior beyond the annotations: partial-success semantics ('returns partial results with a per-domain error instead of failing the whole batch'), rate-limit cost ('debits the rate limiter once per domain'), and caching ('results cache 24h per domain'). These are exactly the traits readOnlyHint/idempotentHint cannot convey. Slightly short of 5 only because failure modes for invalid or private domains beyond the per-domain error shape aren't described.

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?

Four tight sentences, front-loaded with capability then constraints, cache, and use case — almost no waste. Minor redundancy: the cap of 10 is stated in the description and enforced by the schema, and the score range partially duplicates the stated output.

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 and no annotations covering batching, rate cost, or caching, the description supplies all of them plus the return fields (score, grade, llms.txt presence). An agent has everything needed to call it correctly and predict its cost.

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 coverage is 100% (the domains array is fully documented with 1-10 items, min length 3), so the schema carries the heavy lifting. The description adds the meaningful 'public' qualifier and restates the 10 cap, but provides no syntax guidance for the domain-vs-full-URL choice beyond what the schema already says. 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 verb and resource with scope ('Scan up to 10 public domains in one call') and enumerates the exact outputs per domain (visibility score 0-100 with A-F grade, llms.txt existence). It explicitly carves itself out from scan_domain ('No directory coverage'), so an agent can distinguish it from the sibling without opening either schema.

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 positive use case ('outreach research across a prospect list') and routes the alternative explicitly ('No directory coverage (see scan_domain)'). When/when-not guidance is present with the sibling named, leaving nothing to inference.

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