Frankfurter

Frankfurter is a free, open-source exchange rate API for over 200 currencies from over 100 central banks and official sources. Rates update daily and go back to 1948.

GET /v2/coverage describes the default EUR-based daily blended feed. Pass the same base, quotes, and providers filters as a rates query to get its coverage, for example /v2/coverage?base=USD&quotes=ZAR&providers=BIS. Non-daily provider history remains available through explicit provider queries and does not enter the daily blend.

The existing /v2/currencies?scope=all catalogue covers eligible daily sources plus pegged currencies, while /v2/currencies?providers=BIS describes that provider's recognized currencies. Those currency dates, and the dates in /v2/providers, describe publication coverage. They do not establish that a requested base and quote can be converted at the same time. Taking their minimum can advertise history that the default rates query cannot return.

For a website headline describing the default API, use start_date from /v2/coverage:

const coverage = await fetch("https://api.frankfurter.dev/v2/coverage").then(r => r.json());
const headlineYear = coverage.start_date?.slice(0, 4); // Hide the history claim when null.

Use matching filters for pair or provider pages. Both bounds are eligible observation dates at which the selected rates query returns at least one record; they can contain gaps. A carried quote's returned date may precede the first date its base bridge exists. The bounds do not extend history into future days merely because carry-forward can answer them. Multiple quotes use the rates endpoint's semantics: any matching pair suffices. No queryable pair returns null bounds. Coverage accepts only base, quotes, and providers.

The public API runs at https://api.frankfurter.dev. If you prefer to host your own instance, you can run Frankfurter with Docker.

The quickest way to get started:

docker run -d --init -p 8080:8080 lineofflight/frankfurter

For production, mount a volume to persist the SQLite database across container restarts and set any optional API keys:

docker run -d --init -p 8080:8080 \
  -e DATABASE_URL=sqlite:///app/data/frankfurter.sqlite3 \
  -e BAM_API_KEY=your_key \
  -e BANXICO_API_KEY=your_key \
  -e BCCH_USER=your_email \
  -e BCCH_PASS=your_password \
  -e BOT_API_KEY=your_key \
  -e FRED_API_KEY=your_key \
  -e TCMB_API_KEY=your_key \
  -v ./data:/app/data \
  --pull always \
  lineofflight/frankfurter

Without a mounted volume, the database is ephemeral and some endpoints may return empty data until their initial backfill completes.

Some data providers require API keys. All are free and optional:

• BAM_API_KEY — Bank Al-Maghrib (Morocco). Register at apihelpdesk.centralbankofmorocco.ma.
• BANXICO_API_KEY — Banco de México. Register at banxico.org.mx.
• BCCH_USER / BCCH_PASS — Banco Central de Chile. Register at si3.bcentral.cl.
• BOT_API_KEY — Bank of Thailand. Register at portal.api.bot.or.th.
• FRED_API_KEY — Federal Reserve. Register at fred.stlouisfed.org.
• TCMB_API_KEY — Turkish Central Bank. Register at evds3.tcmb.gov.tr.

Backfills are incremental by default. To re-fetch previously omitted quotes from each provider's coverage_start:

FULL=1 bundle exec rake backfill          # All providers
FULL=1 bundle exec rake 'backfill[CBKKW]' # One provider

This inserts missing rows without replacing existing quotes. Per-day APIs can take days to finish. After the backfills finish, run bundle exec rake blend:rebuild to rebuild daily, weekly and monthly blends, then bundle exec rake blend:parity to check materialized results against live computation.

Provider routes retain retired and unknown currency codes. Blends and the currency catalogue exclude unknown codes and observations on or after a currency's terminal date. Early successor labels are relabelled to their configured predecessor. Provider health reports unknown codes for registry updates.

See AGENTS.md for development setup and guidelines.

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