Identify all countries using a specific currency code like USD or EUR. Quickly map currencies to their countries for research or data analysis.
Find all countries that use a specific currency.
Args:
currency: Currency code (e.g., "USD", "EUR", "GBP")
Returns:
List of countries using the currency
| Name | Required | Description | Default |
|---|---|---|---|
| currency | Yes |
| Name | Required | Description | Default |
|---|---|---|---|
| result | Yes |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden, and it only partially discharges it: 'Find all countries' implies a safe read, and the returns line confirms a list comes back. It says nothing about pagination, result size limits, behavior for unknown currency codes, or whether the lookup is case-sensitive.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The purpose sentence is front-loaded and the Args/Returns docstring blocks are compact and easy to scan. The 'Returns' block is somewhat redundant given an output schema exists, but overall nothing is bloated.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a single-required-parameter read tool with an output schema, the description covers the core contract adequately. Usage routing versus sibling lookups is the one genuinely missing piece, but return values need not be re-explained.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 0%, so the description must compensate, and it does by naming the parameter and giving concrete valid values ('USD', 'EUR', 'GBP'). It stops short of stating the expected format (ISO 4217) or case behavior, but the examples add real meaning beyond the bare string schema.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description states a specific verb ('Find') and resource ('countries') with an explicit filter key ('that use a specific currency'). This clearly separates it from sibling lookups like get_countries_by_region and get_countries, which the agent can distinguish without opening either schema.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
There is no guidance on when to prefer this tool over alternatives such as search_countries or get_countries, and no prerequisites or exclusions are stated. The currency filter is implied by the name but never framed as a selection criterion versus siblings.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.