Hopi

CAGR calculator

hopi_cagr_calculator

Read-onlyIdempotent

Work out the compound annual growth rate (CAGR) that takes a starting value to an ending value over a number of years. Returns the annual rate, the total growth and the growth multiple. Source: https://hopi.co.uk/cagr-calculator/

Input Schema

TableJSON Schema

Name	Required	Description
`end`	Yes	Ending value
`start`	Yes	Starting value (must be greater than zero)
`years`	Yes	Number of years over the period (may be a fraction)

Output Schema

TableJSON Schema

Name	Required	Description
`end`	No
`start`	No
`years`	No
`summary`	Yes
`source_url`	Yes	The tool's page on hopi.co.uk (cite or open to check the figure)
`cagrPercent`	No
`growthMultiple`	No
`shortPeriodWarning`	No
`totalGrowthPercent`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 20, 2026
- addedOutput schema / required
```
Added value: +[
+  "source_url",
+  "summary"
+]
```
First observedSep 20, 2026

TDQS

A4.1/5.0

Behavior4/5

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

Annotations already mark the tool as read-only, idempotent, and non-destructive, so side-effect disclosure is not needed. The description adds useful context about the three outputs and includes the authoritative source URL, though it does not mention edge-case handling such as zero ending values or numeric formatting.

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 short sentences with no filler: the first states the core operation, the second lists outputs, and the third provides the source. The most decision-relevant information is front-loaded.

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 simple calculator tool, the description plus full schema descriptions, output schema, and safe annotations cover everything an agent needs to invoke it correctly. No critical information about inputs, outputs, or safety is missing.

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

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema documents all three parameters. The description reinforces the relationship between start, end, and years, but adds no new parameter-level meaning such as units, examples, or formula details beyond what the schema already provides.

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 names the specific operation ('Work out the compound annual growth rate') and the resource relationship ('starting value to an ending value over a number of years'), and enumerates the returned values (annual rate, total growth, growth multiple). This makes it readily distinguishable from related calculators like compound_interest_calculator or percentage_change_calculator.

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

Usage Guidelines3/5

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

The usage context is implied by the CAGR definition, but there is no explicit when-to-use/when-not-to-use guidance or reference to sibling alternatives. An agent must infer that this is the right tool for CAGR rather than the closely related compound interest or inflation calculators.

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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