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

Beyond the annotations (readOnlyHint=false, destructiveHint=false), the description discloses the real side effect: credits become spendable and a credit.purchase entry is appended with credits_added. It also warns that this is TEST only, which matters for an agent deciding whether to invoke it in a real workflow.

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: the action and endpoint come first, followed by the consequence and the TEST-only constraint. There is no wasted wording or repetition that would slow down an agent.

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, no-output-schema mutation tool, the description provides the essential context: what it does, when credits become spendable, and the TEST-only boundary. It does not describe the response shape or failure modes, but those are not required to invoke the tool correctly.

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 schema already covers the sole parameter at 100% and explains it as a PaymentIntent id (pi_…) from checkout_credits. The description adds no additional parameter-level semantics, so the baseline 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?

The description states a clear action ('Confirm a TEST PaymentIntent'), names the endpoint, and explains the credit-lifecycle effect (credits become granted/spendable). It is immediately distinguishable from siblings like checkout_credits, which creates the PaymentIntent rather than confirming it.

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 TEST-only restriction is explicit, and the parameter schema ties the PaymentIntent id to checkout_credits, giving an agent the right sequencing. It does not name alternative tools or spell out when-not-to-use cases beyond the TEST restriction, so it falls just short of a 5.

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