Single tool with reasonable naming and description, but critical gaps in schema documentation, parameter descriptions, and error handling guidance. The tool is explicitly registered via @mcp.tool() decorator in server.py and accepts structured input with defaults. However, the output schema is undocumented, and parameter descriptions lack actionable constraints (format, valid ranges, examples of valid currency codes). Error handling returns generic error objects without recovery guidance. Tool follows verb_noun naming convention (get_exchange_rate) which is positive, but lacks the rigor expected of production-grade tools.

• Document the output schema explicitly in the tool docstring. Example: 'Returns: {"rates": {<target_currency>: <exchange_rate>}, "base": <source_currency>, "date": <ISO_date_string>}' so the LLM knows what fields to expect.
• Replace free-form parameter descriptions with formal constraints. Define currency_from and currency_to as enums of valid ISO 4217 codes, or at minimum document: 'Must be a 3-letter ISO 4217 currency code (e.g., USD, EUR, GBP). Invalid codes return error.' Add pattern constraint in schema if using JSON Schema.
• Specify the accepted date format for currency_date parameter. Document: 'Either the string "latest" for the most recent rate, or an ISO 8601 date string (YYYY-MM-DD) for historical rates. Default: "latest".'
• Enhance error messages with recovery guidance. Replace 'Invalid API response format' with 'Unable to parse API response. Upstream service may be experiencing issues. Retry the request in a few moments.' Replace 'API request failed: {e}' with specific guidance: if 404 → 'Currency code not found; verify ISO 4217 codes.'; if timeout → 'Service request timed out; retry.'; if auth → 'Service authentication failed; check API configuration.'
• Expand tool description to 100 - 200 characters. Example: 'Fetch the current or historical exchange rate between two currencies. Returns exchange rates for the target currency relative to the source. Use this to answer questions about currency conversion rates, historical exchange data, or currency value comparisons.'
• Add validation inside the tool to catch invalid currency codes early and return a clear error with examples of valid codes: 'Invalid currency code: "XYZ". Valid codes include: USD, EUR, GBP, JPY, CAD, AUD. See https://en.wikipedia.org/wiki/ISO_4217 for a complete list.'

Inferred effective spec: <=2025-11-25.

• Relies on Logging (deprecated) - log to stderr or use OpenTelemetry