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

With no annotations, the description carries the burden. It discloses the measurement basis (EIP-3009 authorization spend), the scope (on-chain, Arc USDC), and the inclusion of Circle's facilitators. It also notes the tool is 'Free', which is a behavioral/access trait. It does not mention pagination or rate limits, but the single optional limit parameter covers the main behavioral control.

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 description is a single dense sentence that front-loads the core purpose and then lists the output dimensions. Every clause adds information: measurement basis, scope, output fields, flow shape, and the Circle facilitator addition. No filler or repetition.

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 read-only analytics tool with one optional parameter and no output schema, the description is nearly complete. It tells the agent what data it returns and the measurement basis. The only missing context is what 'flow shape' means precisely (direct, circular, concentrated, self or contract are listed but not defined), and there is no explicit statement about the return format. These are minor gaps given the tool's simplicity.

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% for the single parameter, so the schema already documents 'limit'. The description does not add detail about the limit's effect beyond what the schema says (default 15, max 60). Baseline 3 is appropriate because the schema carries the parameter meaning fully.

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?

The description states a specific verb ('settles'), a resource ('x402 payments on Arc'), and a precise measurement basis ('every relayer that spent an EIP-3009 authorization on Arc USDC'). It also enumerates the exact outputs (settlements, payers, payees, volume, flow shape) and names the two facilitator categories. This clearly distinguishes it from siblings like arc_x402_stats or x402_inspect.

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 implies when to use it: when you need relayer-level settlement detail on Arc, including Circle's facilitators. It does not explicitly state when not to use it or name alternatives, but the specificity of 'measured on the chain' and the relayer focus provides clear context. A small gap: no explicit exclusion of other x402 tools.

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