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

With no annotations, the description carries the full burden and does so well: it discloses that RZP is a HISTORICAL register whose records can stop updating in 2016, that a positive result is not proof of current plátcost, and that the response includes registerState plus a caution field when the two sources disagree. These are behavioral traits an agent could not infer from the schema.

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?

Three tight sentences, front-loaded with what the tool returns, followed by the historical-register caveat and the batching limit. No filler, and the most decision-relevant warning is placed where an agent will see it.

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?

The tool has no output schema, and the description compensates by naming the result fields (registerState, caution) and explaining their meaning. Combined with the source caveat and batching limit, an agent has everything needed to call it and interpret the answer.

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?

There is a single parameter with 100% schema description coverage, and the description's only addition is 'Batch up to 20 IČOs', which restates the maxItems constraint already in the schema. It does clarify that IČOs or DIČs are accepted in CZ+10 format, but that too is in the schema. 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?

It states a specific verb and resource — plátce-DPH (VAT payer) status — and names the exact data sources (ARES RZP record cross-checked against the ARES DPH flag), so an agent can tell it apart from address_check or company_lookup. It never names a sibling tool explicitly, though, so the differentiation is inferred from source specificity rather than stated.

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 gives an explicit scope ('Batch up to 20 IČOs') and a clear when-not with an alternative: a positive from the historical RZP register is not proof of current status, and for a legally binding check the agent should go to the MOF DPH register (ADISREG). That is exactly the when/when-not/alternative routing an agent needs.

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