Compute VAT to add tax to a net amount or extract tax from a gross amount using a supplied rate and inclusive/exclusive mode.
VAT helper. Rate (percent) must be supplied. mode 'exclusive' = amount excludes tax, 'inclusive' = amount includes tax.
| Name | Required | Description | Default |
|---|---|---|---|
| mode | Yes | ||
| amount | Yes | ||
| ratePercent | Yes |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full behavioral burden, and it leaves key traits undisclosed: what the tool returns (tax amount, net, gross, or all three), rounding behavior, and whether ratePercent is a fraction or percent (partially implied by the name). It does state the rate-supply requirement, which is a small but real disclosure.
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?
Three short sentences, front-loaded with the operation and its required input, then the mode semantics. The opening 'VAT helper' is mildly redundant with the tool name, but nothing else is wasted.
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 three-required-parameter calculator with no annotations and no output schema, the description covers inputs adequately but says nothing about the return value, which an agent cannot infer from structured fields. Rounding/precision behavior is also unstated, leaving a meaningful gap for a numeric tool.
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 0%, so the description must compensate. It defines what 'exclusive' and 'inclusive' mean in relation to the amount, adding genuine semantic meaning beyond the bare enum values, and clarifies that ratePercent is a percent. Only 'amount' is left undefined, but its meaning is self-evident.
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 name plus 'VAT helper' and the mode definitions make it clear this computes VAT on an amount, and it distinguishes the two calculation directions. It does not explicitly differentiate from siblings, but no sibling tool is VAT-related, so ambiguity is low.
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?
There is no when-to-use guidance, no statement of when this is preferable to computing manually, and no mention of related tools (e.g., currency conversion or number formatting siblings). The only guidance-like content is the prerequisite that ratePercent must be supplied, which is already enforced by the schema's required list.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.