Hopi

Alcohol unit calculator

hopi_alcohol_unit_calculator

Read-onlyIdempotent

Work out UK alcohol units in a drink from its ABV (percentage) and volume (millilitres), using units = ABV x ml / 1000. Optionally give the number of those drinks per week to get a weekly total compared against the NHS low risk guideline of 14 units a week. Source: https://hopi.co.uk/alcohol-unit-calculator/

Input Schema

TableJSON Schema

Name	Required	Description
`ml`	Yes	Volume of the drink in millilitres, e.g. 175 for a medium glass of wine
`abv`	Yes	Alcohol by volume as a percentage, e.g. 12 for 12% wine
`drinksPerWeek`	No	Optional number of these drinks per week, to work out a weekly units total

Output Schema

TableJSON Schema

Name	Required	Description
`ml`	Yes
`abv`	Yes
`units`	Yes
`summary`	Yes
`source_url`	Yes	The tool's page on hopi.co.uk (cite or open to check the figure)

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 20, 2026

addedOutput schema / required

Added value: +[
+  "abv",
+  "ml",
+  "source_url",
+  "summary",
+  "units"
+]

First observedSep 20, 2026

TDQS

A4.5/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent, and non-destructive behavior. The description adds meaningful context: the formula, the optional weekly comparison against the NHS guideline, and a source URL – none contradicting annotations.

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?

Two sentences pack the formula, optional behavior, guideline reference, and source without redundancy. Front-loaded with the core action and formula, all information earns its place.

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?

For a calculator tool, the description provides the calculation formula, optional weekly variant, health guideline comparison, and source. The output schema exists, so no need to describe return format. Nothing essential is missing for correct invocation.

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 covers all parameters with examples (100% coverage), so baseline is 3. The description adds value by explicitly linking abv and ml to the formula and explaining drinksPerWeek's purpose, going beyond what the schema states.

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?

Describes a specific calculation ('work out UK alcohol units') with the exact formula, distinguishing it from generic calculators. The optional weekly total further clarifies scope and differentiates from similar tools like event wine calculators.

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?

Clearly implies when to use (when needing UK alcohol units from ABV and volume), and the optional weekly parameter adds a use case. No explicit alternatives or exclusions, but the context is strong enough for an agent to select it correctly.

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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