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

Annotations already flag a mutating, idempotent, open-world operation; the description adds real value by explaining what the mutation is (credits are added once, matching idempotentHint) and what the on-chain lookup does. It also enumerates the possible outcomes (pending, credited, expired), though it says nothing about failure or error behavior when a payment is never found.

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?

Four short sentences, front-loaded with the purpose, followed by mechanism, return values, and polling advice. Every sentence adds information and nothing 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 one-parameter tool with no output schema, the description covers the prerequisite (a buy_credits_usdc reference), the side effect, the return statuses, and the polling pattern an agent needs to drive the flow to completion.

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% and the single parameter is already documented as 'The reference from buy_credits_usdc.' The description's 'by its reference' restates rather than extends that, so the baseline of 3 applies.

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 (check a buy_credits_usdc quote by reference) plus the side effect (finds the payment on-chain and adds the credits once), and names the sibling that produces the reference, so it is distinguishable from buy_credits_usdc and the other siblings.

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 concrete invocation guidance — poll every few seconds after paying — which tells the agent both when to call and the cadence. It stops short of stating an explicit when-not condition (e.g., do not poll before sending the transfer), so it is clear but not exhaustive.

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