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

With no annotations, the description carries the burden of behavioral disclosure. It outlines returns (VAT status, REGON/KRS, address, account count, request_id) and the unique NRB verification feature. However, it lacks explicit statements on read-only behavior, authentication needs, rate limits, or error handling (e.g., invalid NIP). The description adds context beyond the schema but is not fully comprehensive.

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 description is concise, with three sentences that front-load the tool's purpose and key features. Every sentence adds value: purpose, key capability, use case, and returns. No redundant phrases.

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?

Given the tool's simplicity (2 parameters, no nested objects) and lack of output schema, the description covers all relevant aspects: what it does, when to use it, and key return fields. It misses explicit mention of error states or idempotency, but is largely complete for a lookup 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 the schema already documents both parameters. The description adds minimal extra meaning, such as 'official Ministry of Finance register' and 'unique' account check, but does not clarify formatting or edge cases beyond what the schema provides. Baseline 3 is appropriate.

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 clearly identifies the tool as a Polish VAT whitelist check using the official Ministry of Finance register, specifying it verifies VAT status by NIP and uniquely checks if a bank account (NRB) is registered. The verb 'check' and resource 'VAT whitelist' are specific, and the phrase 'the standard Polish invoice-fraud check before paying a supplier' distinguishes it from sibling tools targeting other countries or registries.

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 explicitly states the use case: 'the standard Polish invoice-fraud check before paying a supplier.' It also notes 'Companies only,' setting boundaries. However, it does not explicitly state when not to use this tool or mention alternatives like other country-specific checks, though the sibling context makes those implied.

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