ares_check_vat_payer

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It goes beyond a simple 'checks status' by explaining the return convention ('if active'), the ARES delay (up to 24h), and pointing to an authoritative alternative. However, it does not state what happens when the entity is not a VAT payer (e.g., returns null/false) or any error conditions, leaving minor 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 compact, using two sentences to convey the core functionality, return value, and a critical caveat. It is front-loaded with the action and resource, with no redundant phrasing.

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?

For a simple 2-parameter tool with no output schema, the description covers the purpose, return value, a caveat, and an authoritative alternative. It is almost complete, but lacks explicit handling for non-registered entities and error scenarios. Given the low complexity, this is strong but not perfect.

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 description coverage is 100%, so the schema already explains both `ico` (Czech IČO) and `expectedDic` (optional DIČ for cross-check). The tool description adds no additional meaning to these parameters beyond the schema, so it meets the baseline without exceeding it.

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 uses a specific verb ('Check') and a clear resource ('whether a Czech entity is registered as a VAT payer based on ARES'), distinguishing it from sibling tools that focus on company lookup, validation, or due diligence. It also specifies the return value ('Returns the IČ DPH (= DIČ) if active'), making the purpose unambiguous.

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 implies when to use the tool (to check VAT payer status via ARES) and provides a clear alternative: the authoritative source is MFČR (adisspr.mfcr.cz) because ARES may be delayed up to 24h. This effectively tells users not to rely on this tool for real-time legally authoritative status, though it does not explicitly state 'use this when...'.

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