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

No annotations, so the description carries the full burden. It usefully discloses built-in standard rates, custom-rate override, and even the x402 price/currency/chain (USDC, eip155:8453). It says nothing about error behavior for unsupported countries, rounding rules, or precedence when both country and rate are supplied.

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?

Front-loaded with the core behavior and the pricing note is worth its place, but the third sentence duplicates the first almost verbatim, wasting ~25% of the text.

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 four-parameter, no-output-schema calculator the description covers what the tool computes, the two operating modes, the rate-override rule, and the cost of a call. Only the precedence between country and rate, and failure handling, remain unstated.

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 100%, so the baseline is 3. The description adds one useful semantic hint — that rate overrides the built-in country rate — but leaves the required-list/schema mismatch unaddressed (rate is listed as required yet described as optional).

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?

Names a specific operation pair (add VAT to net / remove VAT from gross) plus the resource scope (built-in rates for 36 countries, custom override). An agent can immediately distinguish this from the sibling geo_time_eu_vat_validate, which validates rather than computes.

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?

'Use this when an agent needs to add or remove VAT at standard rates for 36 countries' restates the first sentence rather than giving a use/avoid condition. No alternative tool or edge condition (e.g. non-standard VAT regimes, EU VAT validation) is named.

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