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InkVoice — XRechnung & E-Invoicing

by net.inkvoice
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Calculate German VAT

calculate_vat
Read-only

Converts between net, tax and gross for a given VAT rate, in either direction.

Give an amount and say whether it is net or gross, and you get all three figures back rounded to the cent. Germany's rates are 19 % (standard) and 7 % (reduced), but any rate from 0 to 100 is accepted, so this also works for an Austrian or French invoice.

Rounding is half-away-from-zero, the convention invoices and tax authorities use, and the three returned figures always reconcile: net plus tax equals gross exactly, with no cent left over from rounding each separately.

What this does NOT do: it does not decide which rate applies to a supply, handle more than one rate at a time, or know anything about reverse charge, intra-community supply or the Kleinunternehmer rules. It is arithmetic, not tax advice.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
rateYesVAT rate as a percentage, not a fraction: 19 means 19 %, not 1900 %.
basisYesWhether `amount` is the net figure (add tax to it) or the gross figure (take tax out of it).
amountYesThe amount to convert, in the invoice currency. Must not be negative.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observed

TDQS

A4.7/5.0
Behavior5/5

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

Annotations already mark the tool read-only; the description adds meaningful behavioral detail beyond that: half-away-from-zero rounding, exact reconciliation of net + tax = gross, and acceptance of rates 0–100. It also honestly discloses that it is arithmetic, not tax advice.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The purpose is front-loaded in the first sentence, followed by usage, behavioral guarantees, and limitations. The paragraphs are dense but every sentence contributes; there is no fluff or repetition of schema details.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Even without an output schema, the description tells the agent that all three figures are returned, rounded to the cent, and reconcile. It also covers edge acceptance and exclusions, making it complete for a simple arithmetic conversion tool.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

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 extra meaning by explaining the valid rate range (0–100) and how `basis` controls whether tax is added or removed, going slightly beyond the schema descriptions.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Opens with a specific verb and resource: 'Converts between net, tax and gross... in either direction.' It clearly scopes the tool to arithmetic VAT conversion and distinguishes itself from siblings by stating what it does NOT do (rate selection, tax advice).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Clear context is given for when to use the tool, and the 'What this does NOT do' section provides explicit exclusions such as reverse charge and rate determination. It stops short of naming sibling tools as recommended alternatives, so it misses the top score.

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

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