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

Annotations already declare readOnly/idempotent/closed-world, so the safety profile is covered. The description adds real behavioral context beyond that: VAT can be either included in or added on top of the amount, and currency coverage is limited to RUB/USD/EUR/CNY. It does not mention limits or edge cases (e.g. negative or zero amounts), so not a 5.

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 concrete output example, then the VAT behavior, then currencies — a sensible order with no filler. The final English sentence duplicates the opening Russian one, which is mild redundancy rather than waste.

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?

There is no output schema, yet the description supplies two literal example strings including the generated VAT clause, so the agent knows exactly what comes back. For a 5-parameter, single-purpose formatting tool this is sufficient to call it correctly.

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, and the description genuinely adds meaning: it explains vat_included as 'в том числе или сверху' and pairs the VAT-rate concept with a produced output line. That clarifies the interplay between vat_rate and vat_included better than the schema alone, though it still does not document the kopecks enum values.

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?

Names a specific transformation (amount → words) plus the concrete artifact it produces for invoices/acts/contracts, with a worked example. Nothing in the sibling set (decline_name, validate_requisites, working_days) overlaps, so an agent can route correctly without ambiguity.

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?

States the context of use explicitly ('для счетов, актов и договоров') and notes the VAT-line scenario, which is clear guidance on when this tool applies. It stops short of naming when NOT to use it or pointing to an alternative, since none of the siblings compete here.

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