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

With no annotations, the description carries the burden. It usefully discloses that validation is checksum/format only and purely local, but it does not describe what the function returns for valid vs invalid inputs, how multiple/empty parameters are handled, or any explicit side-effect guarantees. Basic transparency, but incomplete.

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?

Two efficient, front-loaded sentences with no redundancy. The validation target, identifier list, and offline property are all conveyed in minimal space.

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 description covers all four identifier types and their validation algorithms, but because there is no output schema it omits the return shape and success/failure signaling. It also leaves unclear that, given zero required parameters, at least one identifier should be supplied, making the calling contract incomplete.

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 must compensate. It adds algorithm-level meaning: IČO mod-11, DIČ as CZ+IČO or birth number, IBAN mod-97 CZ-specific, and variable symbol. It could be stronger by explicitly mapping each algorithm to the exact schema property names and noting that at least one parameter should be provided.

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 a specific action (validate) and resource (Czech identifiers), enumerates the exact types (IČO, DIČ, IBAN, variable symbol), and marks the operation as offline. This distinguishes it from network-based siblings like check_vat, company_lookup, or search_company.

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 phrase 'Pure local, no network' implies this is the offline formatting/checksum alternative to online lookup tools, giving clear usage context. It does not explicitly name sibling alternatives or state when not to use it, so it falls just short of a 5.

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