Agent Tools

fx_convert

Currency converter for invoices, quotes and budgets: convert an amount from one currency into up to 10 others using European Central Bank rates (latest or a past date). Returns rounded amounts, rate, inverse rate and the 7 day change in percent for each target. Price $0.002 USDC per call via x402. Example output: {"source":"European Central Bank via Frankfurter","amount":1250,"from":"USD","rate_date":"2026-10-27","conversions":[{"currency":"EUR","rate":0.89686,"inverse_rate":1.115,"converted":1121.08,"change_7d_pct":0.925}],"change_7d_reference_date":"2026-10-20"}

Tool call template

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": {
      "amount": "<amount>",
      "from": "<from>",
      "to": "<to>"
    },
    "name": "fx_convert"
  }
}

Input Schema

Name	Required	Description
`to`	Yes	Comma list of up to 10 target currency codes
`date`	No	Optional YYYY-MM-DD for a historical rate
`from`	Yes	Source currency code, e.g. USD
`amount`	Yes	Amount to convert, e.g. 1250.50

Schema Changelog

Changes observed during successful MCP inspections.

AddedOct 27, 2026

TDQS

A4.2/5.0

Behavior4/5

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

With no annotations, the description carries the full load and does it well: it discloses the data source (European Central Bank via Frankfurter), that results are rounded, the output fields, and a per-call charge of $0.002 USDC via x402. That pricing disclosure is exactly the kind of behavioral fact an agent needs before invoking, though rate limits or failure modes for unsupported currency codes are not mentioned.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with purpose and key capabilities, then returns, then pricing. The embedded JSON example is long but earns its place because there is no output schema to convey the response shape.

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?

No output schema exists, yet the example output shows the full response - source, rate date, per-target rate, inverse rate, converted amount and 7-day change plus its reference date. Combined with data source and pricing, nothing an agent needs to call this correctly is missing.

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 coverage is 100%, so amount, from, to and date are already documented in the schema, including the 'up to 10 target currency codes' constraint. The description restates the same facts (up to 10 others, latest or a past date) without adding syntax or edge-case meaning, so baseline 3 is right.

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?

States a specific verb (convert) and resource (currency amounts) plus the exact scope: one source currency into up to 10 targets at ECB rates. That 'convert an amount' framing cleanly separates it from the sibling fx_rates, which only serves rates, 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.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives clear context for use (invoices, quotes, budgets) and notes both latest and historical-date modes, which tells an agent when the tool fits. It never names a competing tool such as fx_rates or offers a when-not condition, so the routing guidance is implied rather than explicit.

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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