exchange-rates-mcp-server

Fx Get Rate

fx_get_rate

Read-onlyIdempotent

Get the exchange rate for a currency pair on a given date (default: latest). Returns the rate, the actual rate date (which may differ from the requested date on weekends/holidays — ECB publishes business days only), and source provenance. Cross-rates are triangulated through EUR automatically. A same-currency pair returns a rate of 1, dated to the same publication day any other pair would report for that date. Use fx_convert_currency when you want the converted amount; use this tool when you only need the rate number.

Input Schema

TableJSON Schema

Name	Required	Description
`date`	No	ISO 8601 date (YYYY-MM-DD). Omit for the latest available rate. ECB data starts 1999-01-04. Future dates are not supported.
`base_currency`	Yes	ISO 4217 base currency code (e.g. USD). Call fx_list_currencies to get valid codes.
`quote_currency`	Yes	ISO 4217 quote currency code (e.g. EUR). The rate is expressed as "how many quote units per 1 base unit". Call fx_list_currencies to get valid codes.

Output Schema

TableJSON Schema

Name	Required	Description
`rate`	No	Exchange rate: units of quote currency per 1 unit of base currency.
`error`	No	Present when the call failed. Absent on success.
`source`	No	Always "ECB via Frankfurter" — the upstream data provider.
`rate_date`	No	Actual date of the rate returned.
`rate_type`	No	Always "ECB reference (mid-market)" — these are reference rates, not tradeable bid/ask.
`date_snapped`	No	True when the API returned a different date than requested — ECB silently snaps weekend/holiday requests to the prior business day.
`base_currency`	No	The base currency code.
`quote_currency`	No	The quote currency code.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 12, 2026

changedInput schema / properties / quote_currency / description

Previous value: -"ISO 4217 quote currency code (e.g. EUR). The rate is expressed as \"how many quote units per 1 base unit\"."New value: +"ISO 4217 quote currency code (e.g. EUR). The rate is expressed as \"how many quote units per 1 base unit\". 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",
+      "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",
-  "rate",
-  "rate_date",
-  "date_snapped",
-  "rate_type",
-  "source"
-]

First observedJun 7, 2026

TDQS

A4.6/5.0

Behavior5/5

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

Annotations already cover safety (readOnly, idempotent, openWorld), and the description adds substantial behavioral context beyond them: the returned rate date may differ from the requested date because ECB publishes business days only, cross-rates are triangulated through EUR, same-currency pairs return 1 dated to the normal publication day, and provenance is included. These are non-obvious behaviors an agent could not infer from annotations.

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-loads purpose and return shape before edge cases, and every sentence carries information. It is slightly dense, running four clauses long with the same-currency edge case, which is useful but secondary to tool selection.

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?

An output schema exists so return values need no elaboration, yet the description still covers the holiday/weekend date fallback, triangulation, the same-currency edge case, and sibling routing. Nothing an agent needs to call this correctly and interpret the result is missing.

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 description coverage is 100%, so the baseline is 3, but the description adds semantics the schema does not: the default for an omitted date is the latest available rate, and rates for pairs without a direct quote are triangulated via EUR rather than failing. It does not restate the ISO 4217 directionality, which the schema already covers.

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+resource (get the exchange rate for a currency pair on a given date) with an explicit default, and distinguishes itself from fx_convert_currency by output type (rate number vs converted amount). An agent can differentiate it from the conversion sibling 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?

Explicitly routes the agent: 'Use fx_convert_currency when you want the converted amount; use this tool when you only need the rate number,' and points to fx_list_currencies for valid codes via the schema. It does not, however, resolve the closest-looking sibling, fx_get_rates, so the single-vs-multiple choice is left 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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