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

Annotations cover the safety profile (readOnly, idempotent, openWorld), and the description adds behavior beyond them: which external sources are queried (OFAC SDN, DNS/domain-age lookups), the possible risk outputs (low|medium|high|unknown), example flags, and a per-call price with a free trial. That is genuinely useful context an agent cannot get from the annotations alone.

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 purpose, then routing rule, then input constraint, then price. Every sentence carries distinct information; nothing is padding.

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?

Because an output schema exists, the description need not enumerate return fields, and it still briefly previews the risk levels and flags. Combined with the routing rule, input constraint, and pricing, an agent has everything needed to call it 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?

Schema coverage is 100%, so the per-field meanings are already documented. The description nonetheless adds a cross-field constraint not expressible in the schema ('provide at least one of domain, address, or name; inputs may be combined'), which is real added meaning, though the domain format note mostly duplicates the schema example.

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+resource (screen a payee wallet address/name/domain) and names exactly what it checks against (OFAC SDN list, domain registration age, DNS). It is clearly distinguishable from the sibling preflight_payment, which is explicitly called out as the different tool.

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 explicit when-to-use ('standalone payee screening before paying') and when-not ('for an x402 challenge or cart and an allow/hold/block spending-rule decision, use preflight_payment instead'), naming the alternative and the condition that selects it.

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