Hopi

Heart rate zone calculator

hopi_heart_rate_zones

Read-onlyIdempotent

Estimate maximum heart rate and five training zones (bpm) from age. Max HR = 220 - age. Method 'max' uses percentages of max HR (50-60, 60-70, 70-80, 80-90, 90-100%). Method 'karvonen' uses heart rate reserve and needs restingHeartRate: zone = (maxHR - resting) x intensity + resting. Source: https://hopi.co.uk/heart-rate-zones/

Input Schema

TableJSON Schema

Name	Required	Description	Default
`age`	Yes	Age in years
`method`	No	'max' (percentage of max HR) or 'karvonen' (heart rate reserve). Default 'max'	max
`restingHeartRate`	No	Resting heart rate in bpm, required for the Karvonen method

Output Schema

TableJSON Schema

Name	Required	Description
`age`	Yes
`zones`	Yes
`method`	Yes
`summary`	Yes
`source_url`	Yes	The tool's page on hopi.co.uk (cite or open to check the figure)
`maxHeartRate`	Yes
`restingHeartRate`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedSep 20, 2026

addedOutput schema / properties / restingHeartRate / type
```
Added value: +[
+  "number",
+  "null"
+]
```

addedOutput schema / required

Added value: +[
+  "age",
+  "maxHeartRate",
+  "method",
+  "restingHeartRate",
+  "source_url",
+  "summary",
+  "zones"
+]

First observedSep 20, 2026

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 and idempotent, and the description adds the exact formulas and intensity ranges used. This makes the calculation behavior fully predictable beyond the structured metadata, with no contradiction.

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?

Three sentences deliver the purpose, the max-HR formula, both methods, and a source link without wasted words. The main purpose is front-loaded before implementation 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?

Combined with a fully described schema, a clarifying output schema, and read-only/idempotent annotations, the description covers everything needed to invoke the tool correctly. Nothing essential is missing.

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?

The schema already documents all three parameters, so the baseline is 3. The description adds value by linking 'restingHeartRate' to the Karvonen formula and by explaining what 'method' and its intensity percentages mean operationally.

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?

The description states a specific verb and resource: 'Estimate maximum heart rate and five training zones (bpm) from age.' It also differentiates the two computation methods, making the tool's scope unmistakable even within a large sibling list of 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?

The description gives clear context for choosing between 'max' and 'karvonen', explicitly noting that Karvonen requires restingHeartRate. It does not name sibling alternatives, but none of the nearby calculators appear to be direct heart-rate-zone competitors.

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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