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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open-world), and the description goes well beyond them: it discloses that the index under-reports so counts are a floor, the exact price ($0.02/call over x402 on Base), the prepaid x-credit-token header option, the 1 free call/day tier, and that no wallet or API key is required. This is exactly the extra behavioral context an agent needs before paying.

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?

Front-loads the core purpose and data-quality caveat before the pricing block. It is dense but every sentence carries material information (caveat, payment models, auth); minor marketing flavor like 'real usage not a guess' and the disclaimer slightly dilute 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 an output schema present, return values need not be spelled out, and the description still supplies the demand-metric definition, the under-reporting caveat, and full payment/auth context. Nothing an agent needs to select and correctly invoke this paid tool 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%, with payTo and query both documented in the schema. The description restates that query is required and that payTo scopes to one seller, adding little beyond what the schema already provides – the baseline 3 for a fully covered schema.

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: reads the CDP discovery index for a capability keyword and reports a competitive picture (match count, distinct sellers, price range, networks, 30-day demand). The scope is clear enough to distinguish it from index/analysis siblings, though it never names an alternative such as x402_seller_check to sharpen 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?

Gives clear context for use – 'For a builder choosing what to ship or an agent picking a provider' – and notes that passing payTo scopes to one seller. It lacks explicit when-not-to-use or named alternative routing, so it stops just short of a 5.

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