Hopi

UK inflation calculator

hopi_inflation_calculator

Read-onlyIdempotent

Adjust a money amount for UK inflation. Mode 'cpi' uses the ONS monthly CPI index (2015 = 100) between two months from January 1988 to August 2026 and returns the adjusted value, total change and average annual rate. Mode 'custom' compounds a chosen annual rate over a number of years. Amounts in GBP. Source: https://hopi.co.uk/inflation-calculator/

Input Schema

TableJSON Schema

Name	Required	Description
`mode`	Yes	'cpi' uses the ONS CPI index between two months; 'custom' uses your own rate
`years`	No	Custom mode: number of years (0 to 200)
`amount`	Yes	The money amount to adjust
`toYear`	No	CPI mode: ending year (default is the latest year)
`toMonth`	No	CPI mode: ending month (1 to 12, default is the latest month)
`fromYear`	No	CPI mode: starting year (1988 to 2026)
`fromMonth`	No	CPI mode: starting month (1 to 12)
`ratePercent`	No	Custom mode: annual inflation rate as a percentage (-50 to 100)

Output Schema

TableJSON Schema

Name	Required	Description
`mode`	Yes
`years`	No
`amount`	Yes
`summary`	Yes
`source_url`	Yes	The tool's page on hopi.co.uk (cite or open to check the figure)
`ratePercent`	No
`adjustedValue`	Yes
`totalChangePercent`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 20, 2026

addedOutput schema / required

Added value: +[
+  "adjustedValue",
+  "amount",
+  "mode",
+  "source_url",
+  "summary",
+  "totalChangePercent"
+]

First observedSep 20, 2026

TDQS

A4.4/5.0

Behavior5/5

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

Annotations already establish read-only, idempotent, and non-destructive behavior. The description adds meaningful behavioral detail beyond those hints: the CPI mode returns 'the adjusted value, total change and average annual rate', specifies the data source (ONS monthly CPI index), the base year (2015 = 100), the supported date range, and that amounts are in GBP. This gives the agent a clear picture of what the tool does and what it returns.

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 description is compact and well-structured: a single opening sentence states the core purpose, followed by mode-specific explanations and a source link. No words are wasted, and the most important information is front-loaded.

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

Completeness4/5

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

The description covers both modes, return values, currency, source, and the supported date window. The conditional required fields for each mode are left to the schema, which handles them clearly. One minor gap is that the description says the CPI index is available 'to August 2026', while the schema allows toMonth up to 12 and toYear up to 2026, creating a slight ambiguity; overall the tool remains well-specified.

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 already documents all 8 parameters thoroughly. The description adds useful context about the ONS index and output values, but it does not add substantial per-parameter meaning beyond what the schema provides. A baseline of 3 is appropriate here.

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 clearly states the primary action: 'Adjust a money amount for UK inflation.' It then specifies two distinct modes ('cpi' and 'custom'), what each does, the return values, the currency, and the source. This is a specific verb+resource definition that differentiates it from sibling calculators like compound interest or currency conversion.

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 when to use the tool: it is for UK inflation adjustments, with CPI mode using ONS data and custom mode for a chosen annual rate. It does not explicitly name alternative tools or provide when-not-to-use guidance, but the context is unambiguous 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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