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

Annotations already declare readOnlyHint, openWorldHint, and non-destructive, so safety is covered. The description adds cost context ('Free') and specifies the chain (Base) and x402 endpoint information, which is meaningful behavioral context for a paid-services catalog beyond what the annotations provide.

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?

A single sentence with the free-of-charge fact front-loaded, then the returned fields. Every clause earns its place with no filler.

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 input params and no output schema, the description carries the burden of explaining return contents, and it does so explicitly (prices, endpoints, payment instructions). It could note the format/pagination of the listing, but for a simple discovery call it is effectively complete.

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?

The tool takes zero parameters, so the baseline is 4. There is nothing for the description to clarify, and it correctly omits parameter discussion rather than padding.

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 (Lists) and resource (paid tools/services) and enumerates exactly what is returned: USDC prices on Base, upstream x402 HTTP endpoints, and payment instructions. No sibling tool is a comparable catalog lister, so it is trivially distinguishable.

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 leading 'Free.' is a genuine decision cue telling an agent this call has no cost and is safe for discovery before spending. However, it gives no explicit when-to-use/when-not or routing to an alternative (e.g. quote_check before paying), leaving usage implied rather than stated.

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