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

Annotations already cover the read-only/idempotent/non-destructive profile, and the description adds materially more: the price (0.01 USDC or 5 credits), the free tier (first 5 paid-tool calls per day, no key needed), and the return shape (allow/review/deny plus a trust-provider block with decision, score, evidence, ttl). These are exactly the non-obvious traits an agent needs before invoking 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 trigger condition is front-loaded and every clause carries content (checks performed, return values, pricing). It is dense rather than padded, though the long comma-spliced sentences slow scanning slightly.

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 and no required parameters, the description does the heavy lifting well: it explains the verdict vocabulary, the evidence block, and the payment model. Small gaps remain around passing only a url vs. also a wallet, and what happens when a check cannot be completed.

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 75%, so baseline is 3. The description does add some meaning – 'with company, the register record and EU/UN/UK/US sanctions' tells the agent that supplying company unlocks extra checks – but 'country' is left entirely unexplained in both schema and description, and nothing clarifies how url vs. wallet interact.

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 verb and resource ('reads the seller's own 402 challenge', 'screens every payTo wallet against the OFAC list') and enumerates the composite checks performed. An agent can tell this differs from single-purpose siblings such as domain_check or eu_sanctions_wallet without opening any schema.

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?

Explicit trigger condition: 'Use before an agent pays an x402 endpoint it has not used before'. That is clear when-to-use guidance, but it never names an alternative (x402_pay_guard, x402_sellers, domain_check) or says when to skip this tool.

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