How do I get the yield to maturity and duration of a bond fund by ISIN?

Where it is in the response

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

json
"headlineMetrics": { "yieldToMaturity": "4.12%", "modifiedDuration": "6.8" },
"metrics": { "effectiveDuration": "6.7", "effectiveMaturity": "9.1", "averageRating": "AA-" },
"profile": { "kind": "fixedIncome", "rateSensitivity": "extensive", "creditQuality": "high" }

Where the figure comes from

Bond metrics are read from the factsheet's portfolio-characteristics block. Equity funds return empty strings here and P/E in metrics.peRatio instead; money-market funds carry sevenDayYield, wam and wal.

The request

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

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']['headlineMetrics']['yieldToMaturity'])

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.headlineMetrics.yieldToMaturity);

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

• Yield to maturity is a gross portfolio figure, not a distribution yield and not net of fees.
• Duration and YTM change with markets; data.dataAsOf is usually the month end of the factsheet.

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.