exchange-rates-mcp-server

Fx Get Rates

fx_get_rates

Read-onlyIdempotent

Get all available exchange rates for one base currency in a single snapshot. Useful for bulk comparison and seeding downstream tools. Returns a map of quote currency → rate, the actual snapshot date, and whether a historical date was snapped from a weekend/holiday to the prior business day. Optionally filter to a subset of quote currencies via symbols. Listing the base currency itself in symbols is accepted and returns a rate of 1 for it.

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.
`symbols`	No	Optional list of quote currency codes to filter the response. When provided, must contain at least one currency code — omit the field entirely, not an empty array, to return all ~30 supported currencies (the base is not among them). Including base_currency here is valid — it comes back with a rate of 1.
`base_currency`	Yes	ISO 4217 base currency code (e.g. USD). Call fx_list_currencies to get valid codes.

Output Schema

TableJSON Schema

Name	Required	Description
`error`	No	Present when the call failed. Absent on success.
`rates`	No	Map of quote currency code → exchange rate (units of quote per 1 base).
`source`	No	Always "ECB via Frankfurter" — the upstream data provider.
`rate_date`	No	Actual date of the rates. May differ from requested date on weekends/holidays — ECB publishes business days only; the API silently snaps to the prior business day.
`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. Always false when date is omitted.
`base_currency`	No	The base currency code.

Schema Changelog

Changes observed during successful MCP inspections.

Changed4 schema fields changedSep 12, 2026

changedInput schema / properties / symbols / description

Previous value: -"Optional list of quote currency codes to filter the response. Omit to return all ~30 supported currencies (the base is not among them). Including base_currency here is valid — it comes back with a rate of 1."New value: +"Optional list of quote currency codes to filter the response. When provided, must contain at least one currency code — omit the field entirely, not an empty array, to return all ~30 supported currencies (the base is not among them). Including base_currency here is valid — it comes back with a rate of 1."

addedInput schema / properties / symbols / minItems
```
Added value: +1
```

changedOutput schema / anyOf

Previous value: -[
-  {
-    "not": {
-      "required": [
-        "error"
-      ]
-    },
-    "required": [
-      "base_currency",
-      "rate_date",
-      "rates",
-      "rate_type",
-      "source"
-    ]
-  },
-  {
-    "required": [
-      "error"
-    ]
-  }
-]New value: +[
+  {
+    "not": {
+      "required": [
+        "error"
+      ]
+    },
+    "required": [
+      "base_currency",
+      "rate_date",
+      "rates",
+      "date_snapped",
+      "rate_type",
+      "source"
+    ]
+  },
+  {
+    "required": [
+      "error"
+    ]
+  }
+]

addedOutput schema / properties / date_snapped

Added value: +{
+  "description": "True when the API returned a different date than requested — ECB silently snaps weekend/holiday requests to the prior business day. Always false when date is omitted.",
+  "type": "boolean"
+}

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",
+      "rate_date",
+      "rates",
+      "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 an entry in symbols is not in the ECB currency set. `date_out_of_range`: date is before 1999-01-04 or in the future. `upstream_no_data`: Every requested currency is supported but the ECB published no rates 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",
-  "rate_date",
-  "rates",
-  "rate_type",
-  "source"
-]

Changed1 schema field changedJul 31, 2026

changedInput schema / properties / symbols / description

Previous value: -"Optional list of quote currency codes to filter the response. Omit to return all ~30 supported currencies."New value: +"Optional list of quote currency codes to filter the response. Omit to return all ~30 supported currencies (the base is not among them). Including base_currency here is valid — it comes back with a rate of 1."

First observedJun 7, 2026

TDQS

A3.9/5.0

Behavior4/5

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

Annotations already cover the safety profile (readOnly, idempotent, openWorld), and the description goes further by disclosing non-obvious behavior: weekend/holiday dates are snapped to the prior business day, symbols is a filter not a union, and a base listed in symbols returns 1.0. It still omits caching, rate-limit, or staleness disclosure, so it is strong but not exhaustive.

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?

Four compact sentences, front-loaded with the core purpose, then return shape, then the optional filter, then the edge case. No filler and no repetition of the name or title.

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?

Though an output schema exists (so return values need not be explained here), the description still conveys the shape of the map, the effective snapshot date, and the business-day snapping rule, plus filter and edge-case semantics. For a 3-parameter read tool, an agent has everything needed to call it correctly.

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 description coverage is 100% – every parameter is documented in the schema, including the ISO date format, the ECB 1999-01-04 start, and the empty-array prohibition. The description only restates the symbols edge case (base currency → rate of 1), so it adds little beyond the schema; 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 with clear scope: 'Get all available exchange rates for one base currency in a single snapshot.' The 'all... bulk comparison' framing implicitly separates it from the singular fx_get_rate and from fx_get_timeseries, but no sibling is named, so the differentiation is left to inference.

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?

'Useful for bulk comparison and seeding downstream tools' gives a hint of when this is the right choice, but there is no explicit when-not guidance and no named alternative (fx_get_rate for a single pair, fx_get_timeseries for history). Usage is implied rather than stated.

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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