exchange-rates-mcp-server

Fx Convert Currency

fx_convert_currency

Read-onlyIdempotent

Convert an amount between any two currencies at the latest or a historical rate. Returns the converted amount, the rate used, the actual rate date, and whether the date was snapped from a weekend/holiday to the prior business day. Cross-rates are triangulated through EUR automatically.

Input Schema

Name	Required	Description
`date`	No	ISO 8601 date (YYYY-MM-DD) for a historical rate. Omit for the latest available rate. Frankfurter v1 data starts 1999-01-04. Future dates are not supported.
`amount`	Yes	Amount in the base currency to convert. Must be greater than zero.
`base_currency`	Yes	ISO 4217 source currency code (e.g. USD). Call fx_list_currencies to get valid codes.
`quote_currency`	Yes	ISO 4217 target currency code (e.g. EUR). The amount will be expressed in this currency. Call fx_list_currencies to get valid codes.

Output Schema

Name	Required	Description
`rate`	No	Exchange rate used: units of quote currency per 1 unit of base currency.
`error`	No	Present when the call failed. Absent on success.
`source`	No	Always "Frankfurter v1" — the upstream data provider.
`rate_date`	No	Actual date of the rate used for conversion.
`rate_type`	No	Always "Daily rate (Frankfurter v1)" — these are reference rates, not tradeable bid/ask.
`base_amount`	No	The input amount in the base currency.
`date_snapped`	No	True when the API returned a different date than requested — Frankfurter v1 snaps weekend/holiday requests to the prior business day.
`quote_amount`	No	The converted amount in the quote currency, rounded to 6 decimal places.
`base_currency`	No	Source currency code.
`quote_currency`	No	Target currency code.

Schema Changelog

Changes observed during successful MCP inspections.

Changed6 schema fields changedOct 24, 2026

changedInput schema / properties / date / description

Previous value: -"ISO 8601 date (YYYY-MM-DD) for a historical rate. Omit for the latest available rate. ECB data starts 1999-01-04. Future dates are not supported."New value: +"ISO 8601 date (YYYY-MM-DD) for a historical rate. Omit for the latest available rate. Frankfurter v1 data starts 1999-01-04. Future dates are not supported."

addedInput schema / properties / date / pattern

Added value: +"^(?:\\d{4}-\\d{2}-\\d{2}|latest)$"

changedOutput schema / properties / date_snapped / description

Previous value: -"True when the API returned a different date than requested — ECB silently snaps weekend/holiday requests to the prior business day."New value: +"True when the API returned a different date than requested — Frankfurter v1 snaps weekend/holiday requests to the prior business day."

changedOutput schema / properties / error / properties / data / properties / reason / description

Previous value: -"Machine-readable failure mode. Declared by this tool: `invalid_date_format`: date is not a real calendar date written as YYYY-MM-DD. `unsupported_currency`: base_currency or quote_currency is not in the ECB currency set. `date_out_of_range`: date is before 1999-01-04 or in the future. `upstream_no_data`: Both currencies are supported but the ECB published no rate for this date. Other values are possible when a failure originates below the handler."New value: +"Machine-readable failure mode. Declared by this tool: `invalid_date_format`: date is not a real calendar date written as YYYY-MM-DD. `unsupported_currency`: base_currency or quote_currency is not available in the current discovery or served historical data. `date_out_of_range`: date is before 1999-01-04 or in the future. `upstream_no_data`: Both currencies are supported but the Frankfurter v1 published no rate for this date. Other values are possible when a failure originates below the handler."

changedOutput schema / properties / rate_type / description

Previous value: -"Always \"ECB reference (mid-market)\" — these are reference rates, not tradeable bid/ask."New value: +"Always \"Daily rate (Frankfurter v1)\" — these are reference rates, not tradeable bid/ask."

changedOutput schema / properties / source / description

Previous value: -"Always \"ECB via Frankfurter\" — the upstream data provider."New value: +"Always \"Frankfurter v1\" — the upstream data provider."

Changed1 schema field changedSep 12, 2026

changedInput schema / properties / quote_currency / description

Previous value: -"ISO 4217 target currency code (e.g. EUR). The amount will be expressed in this currency."New value: +"ISO 4217 target currency code (e.g. EUR). The amount will be expressed in this currency. Call fx_list_currencies to get valid codes."

Changed6 schema fields changedAug 25, 2026

changedInput schema / $schema

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

addedInput schema / additionalProperties
```
Added value: +false
```

changedOutput schema / $schema

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

addedOutput schema / anyOf

Added value: +[
+  {
+    "not": {
+      "required": [
+        "error"
+      ]
+    },
+    "required": [
+      "base_currency",
+      "quote_currency",
+      "base_amount",
+      "quote_amount",
+      "rate",
+      "rate_date",
+      "date_snapped",
+      "rate_type",
+      "source"
+    ]
+  },
+  {
+    "required": [
+      "error"
+    ]
+  }
+]

addedOutput schema / properties / error

Added value: +{
+  "additionalProperties": {},
+  "description": "Present when the call failed. Absent on success.",
+  "properties": {
+    "code": {
+      "description": "JSON-RPC error code for this failure.",
+      "maximum": 9007199254740991,
+      "minimum": -9007199254740991,
+      "type": "integer"
+    },
+    "data": {
+      "additionalProperties": {},
+      "properties": {
+        "reason": {
+          "description": "Machine-readable failure mode. Declared by this tool: `invalid_date_format`: date is not a real calendar date written as YYYY-MM-DD. `unsupported_currency`: base_currency or quote_currency is not in the ECB currency set. `date_out_of_range`: date is before 1999-01-04 or in the future. `upstream_no_data`: Both currencies are supported but the ECB published no rate for this date. Other values are possible when a failure originates below the handler.",
+          "examples": [
+            "invalid_date_format",
+            "unsupported_currency",
+            "date_out_of_range",
+            "upstream_no_data"
+          ],
+          "type": "string"
+        },
+        "recovery": {
+          "additionalProperties": {},
+          "description": "Actionable next step for the caller.",
+          "properties": {
+            "hint": {
+              "type": "string"
+            }
+          },
+          "required": [
+            "hint"
+          ],
+          "type": "object"
+        },
+        "retryable": {
+          "description": "Whether retrying may succeed.",
+          "type": "boolean"
+        }
+      },
+      "type": "object"
+    },
+    "message": {
+      "description": "Human-readable description of what went wrong.",
+      "type": "string"
+    }
+  },
+  "required": [
+    "code",
+    "message"
+  ],
+  "type": "object"
+}

removedOutput schema / required

Removed value: -[
-  "base_currency",
-  "quote_currency",
-  "base_amount",
-  "quote_amount",
-  "rate",
-  "rate_date",
-  "date_snapped",
-  "rate_type",
-  "source"
-]

Changed2 schema fields changedJul 31, 2026

changedInput schema / properties / amount / description

Previous value: -"Amount in the base currency to convert. Must be a positive number."New value: +"Amount in the base currency to convert. Must be greater than zero."

addedInput schema / properties / amount / exclusiveMinimum
```
Added value: +0
```

First observedJun 7, 2026

TDQS

A3.8/5.0

Behavior4/5

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

Annotations already cover readOnly/idempotent/openWorld, yet the description still adds real behavior: weekend/holiday date snapping to the prior business day and automatic EUR triangulation for cross-rates. These are traits an agent could not infer from the schema, though it stops short of stating error behavior or precision/rounding rules.

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 zero filler: purpose first, then return values, then the triangulation caveat. Front-loaded and every sentence earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema and full annotations, the description only needs to convey non-obvious semantics, and it does via date snapping and EUR triangulation. Minor gap: no mention of behavior for unsupported dates or rate precision, though the schema covers the former.

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% and the schema already documents date format, the 'latest' sentinel, amount constraints, and ISO 4217 codes with a pointer to fx_list_currencies. The description adds no new parameter-level meaning beyond reiterating latest vs. historical, so baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource: 'Convert an amount between any two currencies.' It implicitly separates itself from fx_get_rate/fx_get_rates by converting an amount rather than returning a bare rate, but it never names those siblings outright, so the differentiation is inferential rather than explicit.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

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

'At the latest or a historical rate' implies when the date parameter applies, but the description gives no explicit when-to-use vs. fx_get_rate or fx_get_timeseries, and no exclusions. Usage is implied rather than guided.

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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