How do I find the benchmark index of a fund by ISIN?

Where it is in the response

Sample for iShares Core MSCI World UCITS ETF (IE00B4L5Y983):

json
"benchmarkName": "MSCI World Index (Net)",
"calendarReturns": { "years": ["2024", "2025"], "fund": [18.7, 21.2], "benchmark": [18.7, 21.1] }

Where the figure comes from

The name is read from the factsheet or KID; for an index ETF it is the tracked index, for an active fund the comparison index the manager chose. Every performance table in the payload keeps the benchmark column so you can compute tracking difference yourself.

The request

bash
curl -s --max-time 300 https://fundfactsapi.com/api/v1/funds/IE00B4L5Y983 \
  -H "Authorization: Bearer $FUNDFACTS_API_KEY" | jq '.data.benchmarkName'

python
import os, requests
r = requests.get("https://fundfactsapi.com/api/v1/funds/IE00B4L5Y983",
                 headers={"Authorization": f"Bearer {os.environ['FUNDFACTS_API_KEY']}"}, timeout=300)
fund = r.json()
print(fund["name"], fund['data']['benchmarkName'])

javascript
const res = await fetch("https://fundfactsapi.com/api/v1/funds/IE00B4L5Y983", {
  headers: { Authorization: `Bearer ${process.env.FUNDFACTS_API_KEY}` },
  signal: AbortSignal.timeout(300_000),
});
const fund = await res.json();
console.log(fund.name, fund.data.benchmarkName);

Sign up at fundfactsapi.com/signup for a key; the Free plan is 15 lookups a month with no card. Without a key, GET https://fundfactsapi.com/api/v1/demo/funds/IE00B4L5Y983 returns the same payload for funds already in the store (30 calls a minute per IP; it never loads a new fund).

Caveats

• Some active funds have no benchmark or only a cash rate; the field is then empty and the benchmark columns are null.
• Net vs gross return variants of the same index are different benchmarks; the string keeps the qualifier when printed.

Several funds at once

POST /funds with { "isins": ["…", "…"], "wait": true } returns the same payload for up to 10 ISINs per call on Starter, 50 on Pro and 200 on Scale. One request is counted per ISIN answered. X-RateLimit-Remaining on every response tells you how many are left this month; a 429 rate_limited response carries Retry-After. Search and /me are free.

A fund nobody has requested in the last 24 hours is loaded on demand from the documents the fund house publishes. That first call takes 15 seconds to about 3 minutes; set your client timeout to 300 seconds and do not fire a second request for the same ISIN while the first is running. Every later call within 24 hours returns from the store in well under a second with cached: true.

Everything else in the payload is listed in the field reference.