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

Annotations already cover the read-only/idempotent safety profile, but the description adds substantive behavior: data is verified against on-chain settlement rather than self-reported call counts, it is free and aggregate-only, payer counts include sampler/grader wallets so they are an upper bound on customers, and it refuses to serve a stale snapshot. These are real operational traits not derivable from annotations.

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 question it answers, then scope, then the free-vs-paid distinction. It is dense and slightly long, but nearly every clause (on-chain verification, sampler-wallet caveat, staleness refusal) carries decision-relevant information rather than filler.

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 no explanation. The description covers scope, data provenance, access tier, known measurement caveat, and failure behavior — everything an agent needs to call a zero-argument read 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?

The tool takes no parameters, so there is nothing for the description to disambiguate; the 0-param baseline applies. No missing parameter meaning exists to compensate for.

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 concrete resource (market-level x402 demand) and scope (settled on-chain USDC on Base, last 24h) with specific metrics: paid seller addresses, total USD settled, distribution by payment count. It also marks the boundary against the per-seller breakdown route, so the agent can tell what this tool does and does not return.

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?

Opens with the exact question it answers ('is anyone actually paying for x402 APIs today') and contrasts it with listings, then names the alternative route (paid GET /v1/x402/demand) and the condition that selects it. When-to-use and when-to-use-something-else are both explicit.

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