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

Annotations only cover readOnly/openWorld/idempotent; the description goes much further by disclosing the payment lifecycle: first call returns a 402 challenge with howToPay.payloadTemplate, the payload is sent as a PAYMENT-SIGNATURE header, nothing is charged for the 402 or for >=400 failures, and the npm package pays automatically. It also discloses that data is refreshed hourly and how revenue is estimated.

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-loaded with the core purpose before the payment mechanics, and every clause carries information. It is dense — several long compound sentences pack metrics, filters, and payment flow together — but there is little filler to cut.

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?

An output schema exists, so return values need not be re-explained. Between the description and schema, an agent knows what the tool returns, how to filter/sort, and the exact two-step payment flow required to complete a call.

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 interpretive meaning beyond the schema: calls-per-payer near 1.0 signals a one-off sweep versus repeat buyers, and minPayers defaults to 3 because fewer payers are usually a seller's own testers. That is real semantic value the schema descriptions do not carry.

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?

Opens with a precise verb+resource: a leaderboard of every seller (host) in Coinbase's public x402 discovery index, with named metrics (paid calls, paying wallets, estimated revenue, median price, networks). This is clearly distinct from siblings like search_x402 and call_x402, which address discovery and invocation rather than aggregate ranking.

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 concrete use cases ("price a product, find who sells what, or pick a provider by evidence") and filter conditions (keyword, network, minPayers). It does not explicitly name an alternative tool to use instead for a different need, so it stops 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.