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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds value beyond that: rate-limiting, the seconds-scale latency, that the data is live, and the enumerated verdict domain (да | нет | не_установлено). It doesn't describe pagination or the error surface beyond the schema's invalid_unp note.

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 lookup and its scope are front-loaded, and the sentences are dense but purposeful; the optional `name` hint and the rate-limit caveat are separate, short statements. The long enumerated list of returned fields is slightly sprawling and partially redundant with the output schema, but it is compactly packed.

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?

An output schema exists, so return values needn't be spelled out, yet the description enumerates them anyway, which is harmless redundancy rather than a gap. For a two-parameter, read-only lookup with full schema coverage and annotations, an agent has enough to call it correctly; the missing piece is only explicit sibling routing.

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 the baseline is 3; the description nonetheless adds meaning by explaining the purpose of the optional `name` parameter (producing a name-match verdict against the registry answer) and confirming the `unp`-driven lookup flow. That is a modest but real increment over the schema's own wording.

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?

It states a specific verb+resource: a live lookup of the Belarusian State Register of Payers by УНП, returning existence/status, address, registration date, tax office, and more. That is unambiguous and far from a tautology. It stops short of naming which sibling tool is the alternative (lookup_company, search_companies), so it doesn't fully differentiate among siblings.

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?

It implies usage context (verify a counterparty from your documents via `unp`, optionally pass `name` for a name-match verdict) and adds operational guidance ('takes seconds; rate-limited'). However it never states when NOT to use this tool or which sibling to prefer for cached/bulk/alternative lookups, so guidance remains implicit.

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