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

The description discloses the mutation behavior ('add per-use tool credits') beyond what readOnlyHint=false and idempotentHint=false convey, and it notes the payment verification step. It does not cover failure/retry behavior, but the key side effect is clearly stated.

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?

Two tight sentences, no fluff. The core behavior is front-loaded, and the prerequisite ordering follows immediately. Nothing extraneous is included.

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 a full input schema, an output schema, annotations, and a clear sequencing statement, the description gives an agent everything needed to call the tool correctly. Return-value details are covered elsewhere, so the description does not need to restate them.

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 adds no new parameter-specific meaning beyond what the schema already provides, but it does not need to since each parameter has an existing description.

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 uses a specific verb-resource pair: 'Verify an x402 payment and add per-use tool credits to the agent.' This clearly distinguishes the tool from related siblings like commerce.credits_requirements and x402.verify, which handle prerequisite steps rather than the final credit purchase.

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 explicitly states the call order: 'Call after commerce.credits_requirements and a completed USDC payment.' This tells the agent exactly when to invoke the tool and makes the prerequisite chain unambiguous.

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