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

Goes well beyond the annotations by disclosing the paid-call economics: 0.025 USDC per call, the chain (eip155:8453), x402 v2, the _meta["x402/payment"] attachment mechanism, and the exact failure mode (returns "payment required", charges nothing). It also names the shape of the return payload, which matters greatly for a tool with no output schema. Nothing here contradicts readOnlyHint=false/openWorldHint=true — the paid external call is consistent with a non-read-only flag.

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 sentences, each doing distinct work: what it returns, when to use it vs. siblings, the return shape, and the payment contract. The capability and the alternatives are front-loaded, and the lengthier payment sentence is justified because an agent cannot invoke the tool successfully without it.

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 compensates by naming the return fields (seed_keywords, total_available, ideas). All three parameters are covered by the schema, and the non-obvious operational blocker — payment attachment and the behavior when it is missing — is fully spelled out, so an agent has everything needed to call it correctly.

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 keywords, language_code, and location_code are already documented with formats, defaults, and even location-code examples. The description adds only the 'one seed phrase' framing plus the 25-result cap, which is at the baseline for a fully-described schema rather than a real semantic addition.

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+resource+scope: up to 25 keyword suggestions from one seed phrase, with the returned metrics named (search volume, CPC, competition) and the upstream source identified. It explicitly names the sibling tools it is not (keyword_metrics, keyword_difficulty), so an agent can distinguish it without opening any 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 the positive selection criterion ("find new phrases around one seed") and then routes to the two alternatives with the condition that selects each: keyword_metrics for exact volumes of keywords already held, keyword_difficulty for ranking difficulty. This is explicit when/when-not/alternative guidance.

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