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

Beyond the supplied readOnly/idempotent/non-destructive annotations, the description discloses the data sources (OFAC SDN, issuer freezes, EIP-55, burn addresses, poison index), the fail-closed rule that 'an unread source is never ALLOW', the EIP-712 signing of results, and the rate limit (20 free/day then $0.005 via x402). It also explains what a key unlocks (payee book, caps, review queue, audit log). This is exactly the behavioral context annotations cannot carry.

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?

Purpose, sources, verdicts, and pricing are front-loaded in a single dense paragraph with little filler. The closing promotional aside (plans from $9/month with a URL) is the one sentence that leans marketing rather than operational guidance, and the paragraph form makes the x402/requirement workflow harder to scan than a short bulleted split.

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 carries the burden of explaining results and does so by naming the four verdicts and the per-check source attribution plus signature. It does not describe the response envelope or field layout, so an agent knows what the answer means but not its exact shape. For a read-only, open-world check tool this is close to complete but not fully.

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 the baseline is 3; the description still adds cross-parameter meaning the schema lacks, notably that passing 'requirement' causes payTo, asset and amount to be read from the 402 body and that chain must still be supplied. It also ties 'payment' to the exhaustion of free checks, which the schema's 'once the free checks are used up' phrasing supports but the description contextualizes.

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 ('check a stablecoin payment before you send it'), enumerates the supported chains and the exact source set consulted, and names the possible outcomes (ALLOW/REVIEW/DENY/COULD_NOT_READ). An agent can distinguish this from generic siblings such as arc_payment_check or sanctions_check because the checks it bundles are spelled out.

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 trigger condition is explicit ('before you send it') and there is a second documented usage mode ('Pass requirement to check an x402 402 response as it arrived'). Pricing and key-gated behavior tell the agent when the paid path applies. It does not name a sibling alternative or say when NOT to use it, 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.