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

Annotations already declare readOnlyHint=true, so safety is covered; the description goes further by disclosing that the call is STATELESS and persists nothing, that a calculation id is returned for later recording, and what the response contains (per-jurisdiction rates, total_tax_amount, totals). It does not mention auth requirements, rate limits, or error behavior for international/unsupported jurisdictions.

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?

Four sentences, front-loaded with the core action and the statelessness constraint before the input requirements and unit convention. No filler, and the sibling pointer is appended where it is most useful rather than up front.

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 4-parameter nested-object tool with no output schema, the description covers the action, statelessness semantics, required inputs, unit convention, and a summary of the return payload. Nothing an agent needs in order to call it correctly is missing.

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% and nested objects are fully documented, so the schema carries the parameter burden. The description restates the alternative requirement (reference_product_id OR product_category) and the smallest-unit currency rule, both of which already appear verbatim in the schema, adding little beyond the baseline.

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+resource ('Calculate sales tax / VAT for an order') and immediately qualifies the scope as a stateless quote, which distinguishes it from the sibling write tools. It also names where persistence would happen instead (numeral_create_transaction), so an agent can route without reading any schema.

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?

Explicitly says when to use it (quoting tax) and when to use something else (recording the transaction, via numeral_create_transaction with the returned calculation id). It also states the minimum inputs needed to invoke it, so both the when and the how are covered.

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