apply_credit

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

Annotations already mark readOnlyHint=false, so a write operation is expected. The description adds valuable context beyond that: 'ДЕНЬГИ: списывает средства со счёта' (MONEY: debits funds from the account), which warns the agent that real financial impact occurs. This does not contradict the annotations; it enriches them.

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 short sentences, front-loaded with the purpose and followed by a financial warning. The structure is efficient, though the second sentence adds some redundancy with 'с кредитного баланса' repeated as 'со счёта', making it slightly less crisp than an ideal one-sentence definition.

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 simple 3-parameter tool with no output schema, the description covers the essential context: what the tool does, the full/partial scope, and the financial side effect. It does not state prerequisites like needing sufficient credit balance, but this is arguably obvious from 'credit balance' and the schema's confirm flag.

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 all three parameters (amount, confirm, invoice_id) are already documented in the schema. The description adds no additional meaning about the parameters themselves, which is acceptable given the schema's completeness; the baseline of 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 precise action and resource: 'Оплатить инвойс полностью или частично с кредитного баланса' (pay an invoice fully or partially from the credit balance). This clearly distinguishes it from sibling tools like mass_pay, generate_due_invoice, or get_credit_history, and the parenthetical '(whmcs/apply_credit)' reinforces the underlying operation.

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: the tool is for paying an invoice from credit, either in full or partially. It does not explicitly mention alternatives or exclusions (e.g., 'use mass_pay for multiple invoices'), so it stops short of a 5, but the 'fully or partially' scope provides enough situational guidance.

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