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

With no annotations, the description carries the burden well: it discloses the $0.50 USDC-on-Base x402 fee, the exact two-step payment handshake (unpaid call returns payment_required, then PAYMENT-SIGNATURE/X-PAYMENT header), the $0.10 price gate on the seller, the re-run window, and privacy behavior for contact_email and the public flag. It leaves gaps around failure modes and what the paid call costs the seller, but the disclosure is far above baseline for a paid tool.

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?

The value proposition and the price/behavior facts are front-loaded, and the Args list is efficient and scannable. The payment paragraph is dense and slightly repetitive about header versions, but every sentence carries actionable information, so waste is minimal.

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 complex paid tool with no output schema and no annotations, the description covers pricing, the payment flow, the price gate, parameter meanings, privacy, and even the shape of the returned report. Remaining gaps are minor: failure/timeout behavior and whether the tool's own fee differs from what the seller charges during the live 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 description coverage is 0%, so the description must compensate, and it does: it documents all six parameters, including constraints the schema lacks (url must be https, method restricted to GET/POST, body falls back to the seller's own example and never invents data, contact_email stored but never published, public means indexed with private as default). Each note adds meaning beyond the bare schema types.

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?

Specific verb and resource: an independent test of an x402 seller endpoint that runs free checks plus one real paid call. It clearly conveys what it produces (a report with checks, transaction links, pass/warn/fail, findings and fix hints). It does not name the close sibling check_x402_endpoint, so the distinction between this and the free-check-only tool is only implied.

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?

The description gives clear context for use (find out if agents can actually pay you) and a concrete precondition: the paid call only happens if the seller's price is at most $0.10, plus a one-free-re-run-within-7-days policy. It does not explicitly say when NOT to use it or name check_x402_endpoint as the cheaper alternative for free-only validation.

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