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

With no annotations, the description carries the full burden of behavioral disclosure. It explains important business effects: partial payments are allowed, full payment activates the subscription, and overpayments become credit for the next subscription. This goes beyond simply saying 'logs payment' and provides meaningful side-effect context, though it does not mention failure modes or idempotency.

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?

The description is organized with a clear functional statement, two sentences of business context, a @param list, and a @return note. Every sentence contributes meaning, and there is no fluff. It is slightly verbose due to the business context, but that context is valuable and earns its place.

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?

The description covers the tool's purpose, key business rules, all parameters with semantics, and return format (a JSON object in the 'values' object). Given the tool's moderate complexity and the presence of an output schema, this is fairly complete. It could be improved by noting any prerequisites, such as invoice existence or payment validation, but overall it provides a solid understanding.

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 has 0% coverage, but the description compensates with @param tags that explain the meaning of each parameter: invoice_id as customer's database ID, amount_paid as decimal, and customer_payment_reference as optional. This adds value beyond the raw schema. However, it does not mention the schema's default of 'Paid' for customer_payment_reference, a minor gap.

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 clearly identifies the tool's core action with a specific verb and resource: "Logs payment of an invoice." It distinguishes itself from sibling payment tools by explaining that invoices can be paid in micro-payments and that subscription activation only occurs when paid in full, which is unique to this logging function.

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 implies when to use the tool (for logging invoice payments, especially partial micro-payments) but does not explicitly state when to use it over alternatives like paywall__pay_subscription_with_wallet or paywall__payment_3d_secure_link. No exclusions or alternatives are mentioned, so guidance is implied rather than explicit.

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