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

The annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint=false, so the safety profile is fully covered and carries little burden. The description adds the rate whitelist and VND scope as useful context, but it does not say what the tool returns and does not address rounding for integer VND amounts during extraction. That leaves a real gap for a calculation 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 definition is two compact clauses, front-loaded with the core operation and then the currency and locale qualifier. It wastes little, though the bilingual duplication repeats the same content without adding new meaning.

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 simple three-parameter calculator with rich annotations and 100% schema coverage, it is mostly adequate. But with no output schema, the description should say what is returned (net, VAT amount, gross) and how fractional extract results are rounded, and it omits both.

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%, so all three parameters are already documented, with enums for vat_rate and direction. The description restates the direction semantics and the currency and adds no format or edge-case detail beyond the schema, which puts it at 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?

The description names a specific verb pair and resource: add VAT to a net price or extract VAT from a gross price. It adds the domain (Vietnam, VND) and the allowed rates 0/5/8/10, which separates it cleanly from siblings such as build_quote and calculate_selling_price.

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?

Usage is implied by the two directions: use 'add' when you have a net price, and 'extract' when you have a gross price. However, the description never routes the agent among the sibling tools, and it does not explain when to use this instead of build_quote or calculate_selling_price.

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