Foreign-exchange rate between two currencies.
Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.
{
"id": 1,
"jsonrpc": "2.0",
"method": "tools/call",
"params": {
"arguments": {
"from": "<from>"
},
"name": "fx"
}
}| Name | Required | Description | Default |
|---|---|---|---|
| to | No | Target currency, e.g. USD | |
| from | Yes | Source currency, e.g. EUR |
Changes observed during successful MCP inspections.
Input schema / properties / fromAdded value: +{
+ "description": "Source currency, e.g. EUR",
+ "type": "string"
+}Input schema / properties / toAdded value: +{
+ "description": "Target currency, e.g. USD",
+ "type": "string"
+}Input schema / requiredAdded value: +[
+ "from"
+]Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations exist, so the description carries the full disclosure burden and largely drops it. It does not say whether the rate is live or cached, what data source is used, whether an API key/quota applies, or what the response looks like (a bare number, a pair name, a timestamp) — all of which matter for an agent interpreting the result.
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?
A single short sentence with no wasted words and the core concept front-loaded. It is efficient, though its brevity comes at the cost of the disambiguation and return-value detail noted above.
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 two-parameter lookup tool the schema is fully documented, so the minimum is met. However, with no output schema and no annotation coverage, the description should have said what comes back and how to read the rate; that gap leaves the definition just barely adequate.
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 coverage is 100% and both parameters carry examples ('USD', 'EUR'), so the schema already documents the inputs. The description adds no meaning beyond that — notably it does not clarify that there is no amount parameter, i.e. this returns a rate rather than a converted value.
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?
States a specific resource and operation: the foreign-exchange rate between two currencies. An agent can tell it returns a rate rather than doing a conversion, but the description never distinguishes it from the very similarly named siblings convert_currency and currency_list, which is the main ambiguity a caller faces.
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?
No when-to-use guidance at all. With convert_currency, currency_list, crypto, and get_crypto_prices all in the sibling set, the description gives no criteria for choosing this tool over convert_currency (which presumably multiplies by an amount), leaving selection to guesswork.
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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