Currency Exchange · head-to-head
Frankfurter vs National Bank of Poland
Frankfurter aggregates and republishes daily reference rates from roughly 84 central banks, not solely the ECB, covering 200+ currencies with history back to 1948, and supports current, dated, and time-series conversion queries, including filtering to a specific source institution. It's free with no API key and no request quotas beyond abuse-prevention rate limiting, returns JSON by default plus CSV and streaming NDJSON, and now also ships an official self-hosting Docker image and an MCP server for AI-agent integration. The project's site and docs moved from frankfurter.app to frankfurter.dev, with the old domain now redirecting.
The National Bank of Poland's Web API exposes the official mid-market currency reference rates it publishes daily across three rate tables, plus historical gold-price fixings dating back to January 2013 — all queryable by date, currency code, or table series via plain HTTP GET. Responses come back in JSON or XML depending on a format parameter, though historical range queries are capped at 93 days per request. The bank retired plain HTTP in August 2025 in favor of HTTPS-only access.
| Frankfurter | National Bank of Poland | |
|---|---|---|
| Authentication | None | None |
| Pricing | free | free |
| Formats | JSON, CSV, NDJSON | JSON, XML |
| CORS | yes | yes |
| HTTPS | Yes | Yes |
Frankfurter supports 3 response formats, while National Bank of Poland offers fewer — pick Frankfurter for more integration flexibility.