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 states the tool is 'Deterministic; no input. Pure; price 0.0 (free),' which informs the agent about predictability, side-effect-free execution, and cost. It also discloses the return content (country/region, rate, type), which is valuable for a tool without an output schema. However, it does not mention potential list size or ordering, but these are minor for a simple list tool.

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 one concise sentence that front-loads the purpose and includes essential behavioral traits in a compact, scannable format. Every piece of information—'List all built-in VAT and sales-tax rate tables,' the field list, and 'Deterministic; no input. Pure; price 0.0'—is useful and non-redundant.

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?

Given the tool's simplicity (zero parameters, no output schema, no annotations), the description is highly complete. It specifies the data fields returned and the deterministic/free nature. The sibling tax tools are all computational, so the listing purpose is clear. There is no missing information that would prevent correct invocation or interpretation.

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?

The tool has zero parameters, so the baseline is 4. The description reinforces this with 'no input,' and the schema is empty. Since there are no parameters to explain, the description adds no further semantic detail, but none is needed.

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: 'List all built-in VAT and sales-tax rate tables (country/region, rate, type).' The verb 'List' plus the specific resource and fields provide a clear purpose. It distinguishes itself from sibling tools like fx_tax_convert, fx_tax_sales_tax, fx_tax_vat_calc, and fx_tax_vat_validate, which are calculation/validation tools rather than a listing tool.

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 usage context by stating 'no input' and 'deterministic,' indicating it is a straightforward lookup tool for built-in rate tables. It does not explicitly name alternatives or exclusions, but the zero-parameter nature and clear listing function make when-to-use self-evident. A minor gap is not explicitly contrasting with sibling computational tax tools.

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