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

Far exceeds the annotations: discloses credit cost (one ranked-keywords lookup per domain, up to 4 upstream requests), 12h per-domain caching, the top-1000-keywords slice with per-domain coverage fields, and the critical missing-vs-unknown semantics plus the truncated-slice caveat. It also explains the unavailable flag and why empty rows then does not mean no rankings. The readOnlyHint=false is consistent with the credit-charging behavior, so no contradiction.

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?

Purpose is front-loaded and the dense informational sentences each carry distinct value (cost, caching, slice/coverage, missing vs unknown, unavailable, row cap). It is long, but nearly every clause earns its place; the length is driven by necessary semantics rather than padding.

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, the description carries the full return-value burden and does so: it names coverage sub-fields, the 200-row cap vs totalRows, and the unavailable/empty-rows case. Nothing an agent needs to call it or read its result correctly is missing.

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%, so the baseline is 3, but the description adds genuine interpretation beyond the schema: the missing/unknown distinction ('never present unknown as a gap'), the fact that omitting classifications never hides unknown, and that competitorDomains billing is per-domain. These add semantic meaning the enum list alone does not convey.

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 ('compares the project's own domain against up to 3 competitor domains') and a precise output classification set (missing/behind/tied/ahead/unknown). It further distinguishes itself from the sibling by describing itself as 'the inverse of find_serp_competitors, which asks who competes for a keyword set,' so an agent can disambiguate 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?

Explicitly names the alternative (find_serp_competitors) and the condition that selects this tool over it. It also gives a concrete reuse rule — re-run with a different sort or classification filter rather than issuing a new comparison, because lookups are cached 12h — and states the failure precondition (no project domain → validation error).

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