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

Annotations already declare readOnly, openWorld and idempotent, so the safety profile is covered. The description adds genuinely non-schema context: per-call cost ($0.01, free trial first), the required-input invariant, and the risk vocabulary and flag names. It stops short of stating latency or what happens on partial input matches, but that is a minor omission against the annotation coverage.

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 core purpose is front-loaded in the first sentence, followed by return values, input rules, the sibling redirect, and pricing in descending priority. No sentence is redundant.

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 3-param, zero-required read-only screening tool with an output schema present, the description supplies everything needed: purpose, trigger, alternative routing, input combination rules, expected output vocabulary, and cost. Return-format detail is correctly delegated to the output schema.

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 goes beyond it by stating the cross-parameter constraint ('Provide at least one of domain, address, or name; inputs may be combined') and the accepted domain format ('hostname or URL'), neither of which is derivable from the schema alone.

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 ('screens a payee wallet address and name against the OFAC SDN sanctions list') plus the concrete secondary check (domain registration age and DNS). It is immediately distinguishable from preflight_payment and the other siblings, which are named explicitly.

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 an explicit trigger ('Call this before a USDC payment when you only have a payee name, wallet or domain') and names the alternative with the condition that selects it ('For an x402 challenge or cart and an allow/hold/block spending-rule decision, use preflight_payment instead'). Nothing about tool selection is left to inference.

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