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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety and locality need no restating. The description adds real value by disclosing the current scale threshold (no duty up to R1,210,000) and the VAT-vendor exclusion, but stays silent on key behavioral assumptions such as rate-table vintage, natural-person vs company rates, or the returned amount's rounding.

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?

A single sentence front-loads the verb and object, with the threshold and VAT caveat following immediately. No filler, no redundancy with the title.

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?

With no output schema, the description never says what the return value looks like (a Rand amount? a breakdown?) or what assumptions drive the sliding scale. Adequate to invoke, but an agent lacks enough to interpret or defend the result.

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 only 50%, so the description must compensate: it clarifies that the price is Rand excluding VAT and explains the otherwise undocumented meaning of seller_is_vat_vendor (VAT applies instead of duty). It does not explicitly address the default false behavior, but the semantics of both parameters are effectively covered.

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: calculates South African transfer duty payable to SARS on a property purchase. It is clearly distinguishable in subject matter from the numeric siblings (bond_repayment, municipal_rates, purchase_costs), though it never names them or clarifies overlap with purchase_costs.

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?

Implies when the calculation applies and hints that VAT replaces duty when the seller is a VAT vendor, which is a useful branch. It does not say when to prefer this tool over purchase_costs (which may bundle transfer duty) or when the calculation should not be used at all.

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