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

Annotations only indicate a non-read-only, non-destructive operation. The description adds meaningful behavior: it appends a credit.purchase record and makes credits spendable, and it restricts use to test cards/environment. This is valuable context beyond the structured annotations.

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 sentences, front-loaded with the action and test card, followed by the side effect and TEST-only constraint. No filler or redundancy.

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 single-parameter mutation tool with no output schema, the description covers purpose, side effect, and environment restriction. It doesn't mention failure behavior or auth, but those are less critical for a simple test confirmation tool, and sibling workflow is implied by the param description.

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%, and the parameter is clearly documented as a PaymentIntent id from checkout_credits. The tool description does not add additional parameter-level detail, so 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 specific action: confirming a TEST PaymentIntent with Stripe test card pm_card_visa, and identifies the POST /credits/confirm endpoint. It also explains the resulting side effect (credits become spendable, credit.purchase appended), which distinguishes it from lookup tools like credit_balance or quote_credits.

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 gives clear context: this is the point where credits are granted, and it explicitly constrains use to TEST only. It does not name sibling tools like checkout_credits directly, but the parameter schema references 'from checkout_credits,' so the workflow is implied. A more explicit alternative comparison would push this to 5.

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