Citable — keyword volume & difficulty

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

Beyond readOnlyHint/openWorldHint, the description discloses per-call billing, batch-level pricing, answers in request order, null metrics for unknown keywords, licensed clickstream-derived data provenance, and a no-charge fallback if the metrics feed is unavailable. These are behavioral facts an agent could not infer from the schema or annotations, and none contradict the read-only annotation.

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 dense sentences with zero wasted words: cost, deliverable, response behavior, sibling routing, and billing fallback. The most operationally salient fact (price) is front-loaded before the feature list, and each clause adds distinct information.

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 3-parameter read-only tool with no output schema, the description covers the deliverable, input bounds, cost, response ordering, null failure mode, data provenance, and the sibling workflow. Nothing an agent needs to invoke it correctly or interpret its results 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 description coverage is 100%, so the baseline applies: the schema already documents the comma-list format and 1–20 keyword constraint. The description reinforces the batch size and adds the null-response behavior for unknown keywords, but it does not add new parameter-level semantics beyond what the schema already states.

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?

The description names a specific deliverable — 'Search volume, CPC, competition, keyword difficulty and search intent for 1–20 keywords' — with a precise resource (keyword metrics) and a bounded input size. The pairing line with citable_keyword_suggest explicitly differentiates this pricing tool from its closest sibling, so an agent can tell them apart without opening the 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?

'Pair with citable_keyword_suggest: expand a seed there, price the shortlist here' is an explicit workflow rule naming the alternative and the condition that selects each tool. It also surfaces the cost model ('$0.03 USDC per call') as a practical usage consideration, and the 'not charged if the metrics feed is unavailable' line clarifies the billing edge case.

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