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nanwer
by nanwer

convert_currency

Convert a numeric amount between two ISO 4217 currencies using European Central Bank daily reference rates. Useful for trip cost consolidation or price comparisons.

Instructions

Convert a numeric amount between two ISO 4217 currencies using the European Central Bank's daily reference rates.

USE THIS TOOL WHEN:

  • The user asks for a conversion ("how much is ¥30,000 in euros?", "what's $200 in pounds?")

  • You're presenting mixed-currency trip totals (flights in EUR + hotel in USD + activity in GBP) and want to give one consolidated number

  • The user wants to compare prices across vendors quoting in different currencies

Inputs:

  • amount (float, > 0) — the numeric value to convert.

  • from_currency (3-letter ISO 4217 code, uppercase) — e.g. "EUR", "USD", "JPY".

  • to_currency (3-letter ISO 4217 code, uppercase) — e.g. "EUR", "USD", "GBP".

Returns:

  • converted_amount — the result, rounded to 2 decimal places in your response (the raw float is precise).

  • rate — the effective rate (1 from_currency = rate to_currency).

  • rate_date — the ISO date of ECB's published rates. ECB updates daily around 16:00 CET. Weekend / holiday queries return the previous business day's rates — disclose this if the gap is more than 3 days.

  • source — always "ECB".

Powered by the European Central Bank's daily reference rates feed (free, no API key). 29+ currencies covered (USD, EUR, JPY, GBP, CAD, AUD, CHF, SEK, NOK, DKK, INR, MXN, BRL, SGD, KRW, CNY, THB, HKD, NZD, CZK, HUF, IDR, ILS, ISK, MYR, PHP, PLN, RON, TRY, ZAR). If the user names a currency we don't recognize, we return invalid_input.

RESULT PRESENTATION: inline prose, not an artifact. Example: "¥30,000 = €182.45 (rate as of 13 May 2026 via ECB)." For a multi-line trip-cost summary, include the rate_date once at the bottom rather than per-line.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
amountYes
to_currencyYes
from_currencyYes

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Behavior5/5

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

With no annotations, the description fully carries the burden. It discloses important behaviors: weekend/holiday rate staleness, daily ECB updates at 16:00 CET, 29+ currencies, error handling (invalid_input), and return field details. This exceeds basic expectations.

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?

Description is well-structured with clear sections (USE THIS TOOL WHEN, Inputs, Returns, Powered by, RESULT PRESENTATION). However, it is somewhat verbose; a few redundant phrases could be trimmed without losing clarity.

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?

Given the tool has 3 params and no annotations, the description covers all essential aspects: inputs, outputs, behavior, source, limitations (weekend rates), and presentation guidelines. The presence of an output schema reduces the need for return value details, but the description still adds useful context.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters5/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Input schema has 0% description coverage, so the description must compensate. It provides full semantics: amount is numeric >0, from_currency and to_currency are 3-letter ISO uppercase with examples. Also states error condition for unrecognized currencies.

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 it converts a numeric amount between two ISO 4217 currencies using ECB rates. The verb 'convert' is specific and resource is well-defined. No sibling tool performs conversion, so distinction is clear.

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 lists three usage scenarios ('USE THIS TOOL WHEN') including direct conversion requests and mixed-currency totals. It does not provide negative guidance (when not to use) or alternatives, but given sibling tools are unrelated, this is sufficient.

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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