check_vat_status

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

No annotations are provided, so the description carries the burden. It discloses the return format (yes/no/exempt answer plus company name) and describes the check as 'definitive', but it doesn't mention error handling for invalid NIPs, whether any side effects occur, or data source reliability. The description provides some transparency but leaves gaps.

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 and front-loaded, immediately answering 'what does this do?'. The return behavior, use case, and argument format are each explained in a short, purposeful way without any wasted words.

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?

Despite the tool's simplicity, the description covers purpose, return values, a concrete use case, and parameter format. An output schema exists, and the description already clarifies the return structure, making it complete for agent decision-making.

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 0%, so the description fully compensates for the single parameter 'nip' by specifying the format ('10-digit Polish NIP') and allowed formatting ('Spaces and dashes are fine'). This adds practical value beyond the schema's bare string type.

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 states the tool's function with a specific verb ('check') and resource ('NIP registered as an active VAT payer in Poland'). It distinguishes itself from siblings like lookup_company and get_all_rates by focusing specifically on VAT status verification.

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?

Provides clear context for when to use the tool ('useful for fast agent decisions such as 'can I trust this invoice?''). While it doesn't explicitly name alternatives or exclusions, the use case is specific enough to guide selection among the sibling tools.

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