Crypto Fiat: Fetches exchange rates from open.er-api.com for a base currency and returns the target rate and update time 🆓 5 free trial calls per signed wallet
This tool declares no required parameters. Add optional parameters from the input schema as needed.
{
"id": 1,
"jsonrpc": "2.0",
"method": "tools/call",
"params": {
"arguments": {},
"name": "x402-crypto-fiat"
}
}| Name | Required | Description | Default |
|---|---|---|---|
| to | No | ||
| base | No | ||
| symbol | No |
Changes observed during successful MCP inspections.
Input schema / properties / base / descriptionRemoved value: -"Base to process"Input schema / properties / symbol / descriptionRemoved value: -"Symbol to process"Input schema / properties / to / descriptionRemoved value: -"To to process"Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden and does disclose genuinely useful behavioral facts: the upstream data source and the rate-limit/cost model ('5 free trial calls per signed wallet'), which hints at wallet-signed auth. It stops short of explaining error behavior, caching, or rate freshness, and the auth mechanism is only alluded to.
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 front-loaded sentence that names the operation first and the pricing caveat last, with no filler. The emoji and free-trial clause are slightly promotional but do carry information an agent may need.
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 three-parameter tool with no annotations, no output schema, and 0% schema coverage, the definition is thin: the symbol parameter, currency-code format, defaults, and failure modes are all absent. An agent would have to guess at invocation details.
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% and none of the three parameters is annotated, so the description must compensate. It maps loosely onto 'base currency' and 'target rate', but the 'symbol' parameter is never explained and no currency-code format or default behavior is given, leaving half the contract unclear.
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 verb (fetches), resource (exchange rates), the upstream source (open.er-api.com), and the return shape (target rate and update time). It does not, however, distinguish itself from the many near-identical siblings such as x402-currency-rate, x402-forex, or x402-fx-snapshot, so an agent cannot tell from the text why it should pick this one.
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?
The description gives no when-to-use guidance and names no alternative, despite the catalog containing x402-currency-rate, x402-currency-convert, x402-forex, and x402-fx-snapshot. Usage is only implied by the crypto/fiat framing of the name, leaving routing entirely to inference.
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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