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

Annotations already declare a non-read-only, non-destructive, closed-world write. The description adds real beyond-schema behavior: the return value (payment_url), the human-in-the-loop payment flow, and an explicit prohibitive constraint ('Agents must NEVER collect card details'). It stops short of stating auth requirements or whether the invoice expires.

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 core action and return value, and every clause (workflow, method list, card-detail prohibition) carries actionable information. The method enumeration is long but earns its length by disambiguating five enum values.

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?

No output schema exists, and the description supplies the key return value (payment_url) and the surrounding workflow an agent needs to act correctly, while annotations cover the safety profile. Nothing essential is missing for this two-parameter tool.

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 coverage is 100%, so baseline is 3, but the description genuinely enriches the method enum beyond the schema's bare 'Payment method' by explaining each value's audience and defaults. amount_usd adds no new info beyond the schema's min/max, so it is not a full 5.

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 ('Creates an invoice') plus the concrete artifact ('returns payment_url'), which clearly separates it from siblings like buy_proxy, create_account, and get_payment_status. An agent knows exactly what side effect to expect.

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?

Explicitly explains the workflow (hand URL to the human, who pays in the browser) and gives method-selection guidance: sbp default for RU, card_international best for non-RU, crypto_cryptomus as an alternative gateway. It does not name competing sibling tools, but the when-to-use guidance for payment methods is unusually strong.

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