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

With no annotations, the description carries the full burden and does disclose meaningful domain behavior: partial payments are allowed, subscription activation is gated on full payment, and overpayment rolls into credit. It still omits auth/permission requirements, idempotency, and failure behavior for a mutation that triggers a downstream activation.

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?

Front-loaded with the action and its consequences before the parameter tags, with no filler sentences. The closing @return note is vague ('a json object, in the "values" object') but useful given there is no output schema.

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 mutation tool with zero annotations and no output schema, the description covers the workflow and parameters adequately but leaves gaps around permissions, reversibility/duplicate-payment handling, and error cases that an agent calling a payment logger would want.

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 0%, so the description must compensate, and its @param tags document all three parameters: invoice_id as the customer's database key, amount_paid as a decimal, and customer_payment_reference as optional. It adds little about currency/units for amount_paid or expected reference format, so it is strong but not complete.

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+resource ('Logs payment of an invoice') and clarifies the object is an invoice rather than a subscription, which separates it from siblings like customer_log_subscription and customer_payment_history. It stops short of explicitly naming which sibling to use instead, so it earns a 4 rather than a 5.

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 embeds usage context by explaining the micro-payment workflow and that the subscription only activates on full payment, which implies when this tool applies. However, it never states when NOT to use it or which alternative (e.g. pay_subscription_with_wallet, pay_subscription_with_credits) handles other payment paths, leaving routing to inference.

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