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

Annotations already cover readOnly/idempotent/non-destructive/openWorld, so the bar is lower, and the description still adds real behavior: live Coinbase pricing rather than a rate card, a $0.03 per-call x402 charge on Base, a prepaid x-credit-token header for unlimited calls, and no free tier or API key. That billing/auth disclosure is exactly the kind of context annotations cannot express.

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-loads the purpose reasonably well, but the '$100 in the US… card takes 2.44' illustration, 'Not financial advice', and repeated payment boilerplate dilute the signal. The billing facts and required inputs earn their place; the marketing framing does not.

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 an output schema present and rich annotations, the description correctly focuses on what those can't convey: pricing computation model, cost/auth mechanics, and the address-driven checkout mode. Near-complete for the agent's decision, lacking only routing guidance against siblings.

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 restates the required inputs and explains that address produces a payable checkout link, but that meaning is already in the schema, adding little beyond it.

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: prices the same fiat purchase across every payment method a country allows and ranks them by net received. Very specific about output and scope. It does not name or differentiate against the obvious sibling onramp_coverage, so the agent must infer which to pick.

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 operative guidance ('Required inputs: country, amount', 'Pass address= for a payable checkout link') but never states when to use this versus onramp_coverage or the various *_gate / pre_trade tools. Usage is implied rather than delineated.

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