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Migration Guide — Fixer → fastFOREX API

Migrate from Fixer in under an hour

Fixer and fastFOREX API share the same concepts — latest, historical, convert, time-series — with a different base URL and two renamed fields. This guide maps every endpoint and flags the quirks worth knowing before cutover.

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Draft guide — endpoint mapping to be validated against both APIs' current docs before publishing.

Four steps, most of them small.

  1. Get a free API key

    7-day trial, no credit card, full plan access from minute one.

  2. Swap base URL & auth

    data.fixer.io/api → api.fastforex.io, and ?access_key= becomes the X-API-Key header (or ?api_key=).

  3. Rename two fields

    Their "rates" is our "results"; their unix "timestamp" is our ISO-8601 "updated". Drop the "success" flag check — we use HTTP status codes.

  4. Benchmark, then cut over

    Run both in parallel on the trial, compare values and latency, switch when convinced.

Endpoint mapping

Every endpoint, translated.

One row per call your code makes today. Parameters keep their meaning — only names and paths change.

Purpose

Fixer

fastFOREX API

Latest rates (specific symbols)

GET /api/latest?symbols=EUR,GBP

GET /fetch-multi?from=USD&to=EUR,GBP

Latest rates (all currencies)

GET /api/latest

GET /fetch-all?from=USD

Convert an amount

GET /api/convert?from=USD&to=EUR&amount=100

GET /convert?from=USD&to=EUR&amount=100 (identical!)

Historical (single date)

GET /api/2020-01-01 (date as path)

GET /historical?date=2020-01-01

Time-series (date range)

GET /api/timeseries?start_date=…&end_date=… ($59.99+)

GET /time-series?start=…&end=… (every plan)

Fluctuation

GET /api/fluctuation ($99.99+)

Compute from /time-series, or use /fx OHLC endpoints

List currencies

GET /api/symbols

GET /currencies

Authentication

?access_key=YOUR_KEY

X-API-Key header (keeps keys out of logs)

Response shapes

Before and after.

Typically one line changes: data.rates becomes data.results. Drop the "success" boolean check — fastFOREX API signals errors with HTTP status codes, so your HTTP client already handles them.

Before · Fixer
$ curl "https://data.fixer.io/api/
   latest?access_key=KEY&symbols=EUR,GBP"

{
  "success": true,
  "timestamp": 1757490000,
  "base": "EUR",
  "rates": {
    "USD": 1.163,
    "GBP": 0.849
  }
}
After · fastFOREX API
$ curl -H "X-API-Key: YOUR_KEY" \
   "https://api.fastforex.io/fetch-multi?from=EUR&to=USD,GBP"

{
  "base": "EUR",
  "results": {
    "USD": 1.163,
    "GBP": 0.849
  },
  "updated": "2026-09-10T09:39:00Z"
}

Watch for these differences.

The honest list — everything that behaves differently, including the ones that work in your favour.

  1. EUR base lock disappears

    Fixer's free and Basic plans fix EUR as base; switching base is a paid feature. Every fastFOREX API plan supports any base — client-side cross-rate maths can be deleted.

  2. Overage billing model changes

    Fixer auto-bills overages (~$6 per extra 1,000 calls on Basic). fastFOREX API includes 1,000,000 calls and tops up at $18 per additional million — remove any call-rationing logic.

  3. The success flag

    Fixer returns 200 OK with {"success": false} on errors. We return real HTTP error codes — simpler, but check your error handling isn't reading the body for failures.

  4. Check currency coverage

    Fixer lists 170 symbols including Bitcoin, gold and silver as currency codes. Diff /currencies (and /metals/list for gold/silver) against your usage before cutover.

Prove it to yourself

Benchmark both during your trial.

Don't take our 21ms average on faith. Run both APIs from your own infrastructure with this snippet, compare the numbers, and cut over when the data says so.

benchmark.sh · run from your servers
$ for i in 1 2 3 4 5; do
>   curl -s -o /dev/null -w "fastforex  %{time_total}s\n" \
>     -H "X-API-Key: KEY" "https://api.fastforex.io/fetch-all?from=EUR"
>   curl -s -o /dev/null -w "fixer      %{time_total}s\n" \
>     "https://data.fixer.io/api/latest?access_key=KEY"
> done

fastforex  0.022s
fixer      0.048s

Switching support included.

Our team answers 365 days a year and has guided many migrations from this exact provider. Need longer than 7 days to validate? Ask about extending your trial.

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Migration questions.

What teams ask when leaving Fixer.

Can I run both APIs in parallel?
Yes — the recommended path. The 7-day trial has full plan access, so shadow-read against both providers and compare values and latency on production traffic before switching.
Will values match Fixer's exactly?
Close but not identical — different source networks and snapshot times. Fixer blends 16 unnamed sources; we aggregate 100+ named institutional contributors. Benchmark both against a reference you trust.
I use gold and silver codes (XAU/XAG) on Fixer.
Move those calls to our Metals API: /metals/spot gives you gold and silver in any currency, unit and purity, with bid/ask — far richer than a currency-code shim. Available on Premium plans.
Can you help with the migration?
Yes — support answers 365 days a year. If you need more than 7 days to validate, ask about extending your trial.

Something specific to your setup?

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