Verify whether a bank account is assigned to an active Polish VAT taxpayer by NIP or REGON on a given date, using the official VAT White List API.
Check account association with an active taxpayer on YYYY-MM-DD.
id_type: nip or regon. accountAssigned is the API's TAK/NIE answer; API
failures raise errors and must never be interpreted as a negative match.
| Name | Required | Description | Default |
|---|---|---|---|
| date | Yes | ||
| id_type | Yes | ||
| identifier | Yes | ||
| bank_account | Yes |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, this description does real work: it discloses that the result field is 'accountAssigned' reflecting the API's TAK/NIE answer, and warns that API failures raise errors and must never be read as a negative match — an important interpretation trap. It still omits auth requirements and whether the check is read-only or side-effect free.
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 short sentences, front-loaded with the purpose and followed by the two highest-risk clarifications. The unsubstituted 'YYYY-MM-DD' placeholder is slightly confusing, but overall it is tight.
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?
No output schema, and the description only explains one return signal (accountAssigned); it doesn't describe the overall response shape or how a false/absent result is represented. Combined with zero parameter documentation, an agent can guess the call but not confidently interpret all outcomes.
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 carries the full burden. It only documents id_type values ('nip or regon') and gives a date format hint via the literal 'YYYY-MM-DD'; identifier and bank_account are completely unexplained (format, TAK vs NIE, normalization of the account number).
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?
States a specific verb and resource: check whether a bank account is associated with an active taxpayer. The 'check' verb distinguishes it from the sibling search_* tools, which look records up rather than answer an association question. It does not explicitly name search_by_bank_account as the alternative, so differentiation is implicit.
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?
Usage is only implied by the verb 'check' and the phrase 'active taxpayer'. With siblings search_by_nip / search_by_regon / search_by_bank_account that overlap substantially, the description never says when to prefer this tool over them or what preconditions (an active taxpayer existing) mean in practice.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.