exchangerate.dev vs Massive (formerly Polygon.io)

Name: exchangerate.dev — FX rate API
Brand: exchangerate.dev

exchangerate.dev brings intraday FX, daily history, and MCP together in one API.

Verdict

Choose exchangerate.dev when intraday freshness, per-value provenance, MCP-native access, and free-tier headroom matter. Keep Massive (formerly Polygon.io) if you need real-time data, WebSockets, second aggregates, or flat files.

At a glance

Feature	exchangerate.dev	Massive (formerly Polygon.io)
Free tier	10,000 requests/month	5 calls/min; end-of-day
Cheapest paid plan	Basic · $10/month	Currencies Starter · $49/month
Update speed	Major pairs about 60s on trading days	End-of-day free; real-time paid
History	Daily from 1999; varies by pair	2 years free; 10+ paid
Coverage	31 currencies; any supported base	All forex and crypto tickers
Interfaces	REST; MCP; WebSocket on Realtime	REST; WebSocket on Starter
SDKs	Not published	Python and Go clients
Commercial use on free tier	✗ Non-commercial only	Not published

Price at your usage

The lowest published plans for each monthly request volume, with traffic spread across the month.

Requests a month	exchangerate.dev	Massive (formerly Polygon.io)
1,000	Free · $0/month	Currencies Basic · $0/month
10,000	Free · $0/month	Currencies Basic · $0/month
100,000	Basic · $10/month	Currencies Basic · $0/month

Basic supports these volumes at five calls per minute with end-of-day data; current conversion requires Starter at $49/month.

Switch in a few minutes

Massive returns a bid/ask conversion; exchangerate.dev returns an indicative EUR rate per USD.

Massive (formerly Polygon.io)

# Change: URL and auth
curl -G \
  "https://api.massive.com/v1/conversion/USD/EUR" \
  --data-urlencode "amount=1" \
  --data-urlencode "precision=4" \
  --data-urlencode "apiKey=YOUR_API_KEY"

Massive (formerly Polygon.io)

// Change: URL and auth
const url = new URL(
  "https://api.massive.com/v1/conversion/USD/EUR"
);
url.search = new URLSearchParams({
  "amount": "1",
  "precision": "4",
  "apiKey": "YOUR_API_KEY",
}).toString();
const response = await fetch(url, {
  method: "GET",
});
if (!response.ok) {
  throw new Error(String(response.status));
}
console.log(await response.json());

Massive (formerly Polygon.io)

import requests

# Change: URL and auth
response = requests.get(
    "https://api.massive.com/v1/conversion/USD/EUR",
    params={
        "amount": "1",
        "precision": "4",
        "apiKey": "YOUR_API_KEY",
    },
    timeout=10,
)
response.raise_for_status()
print(response.json())

exchangerate.dev

# Change: URL and auth
curl -G \
  "https://api.exchangerate.dev/v1/latest/USD" \
  --data-urlencode "symbols=EUR" \
  -H "Authorization: Bearer YOUR_API_KEY"

exchangerate.dev

// Change: URL and auth
const url = new URL(
  "https://api.exchangerate.dev/v1/latest/USD"
);
url.search = new URLSearchParams({
  "symbols": "EUR",
}).toString();
const response = await fetch(url, {
  method: "GET",
  headers: {
    "Authorization": "Bearer YOUR_API_KEY",
  },
});
if (!response.ok) {
  throw new Error(String(response.status));
}
console.log(await response.json());

exchangerate.dev

import requests

# Change: URL and auth
response = requests.get(
    "https://api.exchangerate.dev/v1/latest/USD",
    params={
        "symbols": "EUR",
    },
    headers={
        "Authorization": "Bearer YOUR_API_KEY",
    },
    timeout=10,
)
response.raise_for_status()
print(response.json())

Why teams switch

Room to test a real workload

10,000 free monthly calls give you room to build around your own traffic pattern, from a small currency converter to a recurring rate lookup. No card is required, and any supported currency can be the base. The usage table maps three monthly volumes to the lowest qualifying plan, making the next step clear as requests grow. Commercial use starts on Basic at $10/month.

Rates with a time and a source

Major pairs update about every 60 seconds on trading days. Responses include source and market-session fields alongside observation timestamps, so your application can show where a value came from and when it was observed. Daily references remain identifiable as daily data. That context belongs beside the number in a customer interface, an internal report, or an agent answer that explains the rate it used.

One account for apps and agents

REST and MCP are included on every plan. Daily history begins in 1999 for many pairs, bringing current lookups and dated records into the same service. A developer can start with the HTTP examples above, then use MCP for agent queries without adding another subscription. The same base and target currencies carry through the workflow, from fetching a current rate to looking up a historical observation.

When they are the better pick

Massive is a better fit for real-time data, WebSockets, second aggregates, or flat files. Currencies Starter includes unlimited calls and over 10 years of history for $49 per month. Basic has 2 years of history and 5 calls per minute.

Questions

Is there a free Massive alternative for FX?

Yes. exchangerate.dev includes 10,000 calls per month and major-pair updates about every 60 seconds on trading days. Massive Currencies Basic is free, with 5 calls per minute, end-of-day data, and 2 years of history.

Is Massive the same service as Polygon.io?

Polygon.io has rebranded as Massive. The former Polygon.io pricing page redirects to Massive pricing. This comparison covers its currencies plans.

When is Massive a better fit?

Choose Massive Currencies Starter for real-time data, WebSockets, second aggregates, or flat files. It costs $49 per month with unlimited calls and over 10 years of history. Basic does not include WebSockets.

Can I use exchangerate.dev Free commercially?

Free is for non-commercial work. Commercial use starts on Basic at $10/month, subject to terms and source rights.

Related comparisons

Get API key

Sources and review date

Reviewed 2026-10-04.