Hopi

Currency converter

hopi_currency_converter

Read-onlyIdempotent

Convert an amount of money from one currency to another using Hopi's live mid-market exchange rates (updated hourly, 150+ currencies). Use ISO 4217 codes such as GBP, EUR, USD, JPY. Source: https://hopi.co.uk/currency-converter/

Input Schema

TableJSON Schema

Name	Required	Description
`to`	Yes	Currency to convert to, ISO 4217 code e.g. EUR
`from`	Yes	Currency to convert from, ISO 4217 code e.g. GBP
`amount`	Yes	The amount to convert

Output Schema

TableJSON Schema

Name	Required	Description
`to`	No
`from`	No
`rate`	No
`amount`	No
`result`	No
`summary`	Yes
`asOfUnix`	No
`complete`	No
`warnings`	No
`source_url`	Yes	The tool's page on hopi.co.uk (cite or open to check the figure)
`rateAgeHours`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed5 schema fields changedSep 20, 2026
- addedOutput schema / properties / asOfUnix / type
```
Added value: +[
+  "number",
+  "null"
+]
```
- addedOutput schema / properties / complete
```
Added value: +{
+  "type": "boolean"
+}
```
- addedOutput schema / properties / rateAgeHours
```
Added value: +{}
```
- addedOutput schema / properties / warnings
```
Added value: +{
+  "type": "array"
+}
```
- addedOutput schema / required
```
Added value: +[
+  "source_url",
+  "summary"
+]
```
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 readOnlyHint=true and idempotentHint=true, so the description need not repeat that. It adds valuable context about rate freshness (updated hourly) and coverage (150+ currencies), plus a source URL, giving the agent insight into data reliability. No contradiction with 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, zero filler. The first sentence front-loads the core purpose and key data properties; the second gives code examples and a source link. Every word earns its place, and the structure is immediately scannable.

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?

The tool is simple: three parameters, all documented in the schema, with an output schema present. Annotations cover safety. The description adds the only missing piece—rate source and update frequency—so an agent has everything needed to invoke it correctly. No gaps.

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% with descriptions for all three parameters. The description adds ISO 4217 code examples (GBP, EUR, USD, JPY) which reinforce the pattern and clarify expected input format, going slightly beyond the schema. This added guidance helps an agent construct valid calls.

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 tool converts money between currencies using live mid-market rates, with a specific verb ('Convert') and resource ('currency'). It distinguishes itself from sibling converters (e.g., area, angle) by explicitly mentioning currency and ISO 4217 codes, leaving no ambiguity about its purpose.

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?

While the description doesn't explicitly state 'use this for currency conversion only', the naming and content make it obvious. It gives clear context (live rates, 150+ currencies) but does not mention alternative tools or exclusions. For a single-purpose converter among many unrelated converters, this is sufficient.

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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