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Frankfurter

by io.github.lineofflight
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Convert currency

convert
Read-only

Convert an amount from one currency to another. Returns {amount, currency} rounded to the target's minor units. Upstream rounds rates per direction; for low-value sources, flip via get_rates for more precision. Pass provider to use one institution's published rate, e.g. UST for a U.S. Treasury reporting rate.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
toYesISO 4217 target currency.
dateNoDate YYYY-MM-DD for a past rate; omit for latest.
fromYesISO 4217 source currency.
amountYesAmount in the source currency. Normalize localized input first: '100,50' -> 100.5; German '1.000,50' -> 1000.5; English '1,000.50' -> 1000.5.
providerNoProvider key, e.g. ECB for European Central Bank or UST for U.S. Treasury reporting rates. Serves that institution's published rates instead of the blend; a date inside a monthly or quarterly provider's period returns the rate in force. Keys at https://frankfurter.dev/providers/.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changed
    • changedInput schema / properties / provider / description
      Previous value: -"Provider key, e.g. UST for U.S. Treasury reporting rates. Serves that institution's published rates instead of the blend; a date inside a monthly or quarterly provider's period returns the rate in force. Keys at https://frankfurter.dev/providers/."New value: +"Provider key, e.g. ECB for European Central Bank or UST for U.S. Treasury reporting rates. Serves that institution's published rates instead of the blend; a date inside a monthly or quarterly provider's period returns the rate in force. Keys at https://frankfurter.dev/providers/."
  2. Changed1 schema field changed
    • addedInput schema / properties / provider
      Added value: +{
+  "description": "Provider key, e.g. UST for U.S. Treasury reporting rates. Serves that institution's published rates instead of the blend; a date inside a monthly or quarterly provider's period returns the rate in force. Keys at https://frankfurter.dev/providers/.",
+  "maxLength": 8,
+  "minLength": 2,
+  "type": "string"
+}
  3. Changed2 schema fields changed
    • changedInput schema / properties / amount / description
      Previous value: -"Amount in the source currency."New value: +"Amount in the source currency. Normalize localized input first: '100,50' -> 100.5; German '1.000,50' -> 1000.5; English '1,000.50' -> 1000.5."
    • changedInput schema / properties / date / description
      Previous value: -"Historical date YYYY-MM-DD. Omit for latest."New value: +"Date YYYY-MM-DD for a past rate; omit for latest."
  4. First observed

TDQS

A4.7/5.0
Behavior5/5

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

Beyond the readOnlyHint annotation, the description discloses the return shape, rounding to minor units, direction-dependent rate rounding, and provider-specific rate behavior. It gives the agent important operational context without contradicting the 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?

Three sentences with no filler. The first sentence defines the core operation, and the subsequent sentences each add a distinct, useful behavioral detail. Everything is front-loaded and relevant.

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?

Even without an output schema, the description states the return shape and key rounding behavior. Provider nuances, date semantics, and the get_rates alternative are addressed either in the description or in the schema, making this complete for a read-only conversion tool.

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%, so the baseline is 3. The description adds extra meaning by explaining provider examples (UST) and the direction-dependent rounding behavior, which is not inferable from the schema alone.

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 a specific action and resource: converting an amount from one currency to another. It also distinguishes itself from the sibling get_rates tool by referencing it for an alternative precision behavior.

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?

The description explicitly tells the agent when to consider get_rates instead (low-value sources, to flip direction for more precision), and when to pass a provider. It does not spell out a comprehensive list of exclusions, but the primary use case is unambiguous and the alternative routing is concrete.

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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