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

Annotations already cover safety (readOnly, idempotent, non-destructive, open-world), and the description adds genuinely non-obvious behavior: each call bills the agency's DataForSEO account, the response reports cost and monthly quota consumption, and same-day repeats are served from cache for free. It stops short of failure modes or what happens when the monthly limit is exhausted.

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?

Three tight sentences: what it returns, what it costs, and how caching affects cost. The core capability is front-loaded and no sentence is redundant.

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?

For a read-only, well-schematized tool with no output schema, the description supplies the missing pieces an agent needs: the shape of the answer (metrics plus cost/quota) and the billing implication. Only edge-case behavior (quota exhaustion, errors) is left unstated.

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 four parameters are already documented, including defaults, bounds and a location format example. The description only echoes the 'most searched first' ordering already present in the limit parameter, adding no new semantic value.

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?

Names a specific resource (keywords related to a seed keyword) and states the returned metrics and sort order, so the agent knows exactly what comes back. It does not explicitly distinguish itself from near siblings like seo__keyword_questions or seo__keyword_metrics, leaving the agent to infer the boundary.

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 implied rather than stated: the caching note ('the same question within a day is answered from Royally's copy at no cost') nudges toward re-asking, but there is no explicit 'use this when X, use sibling Y instead' guidance despite several closely overlapping SEO keyword tools.

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