How do I compare two ETFs or funds programmatically?

Fetch both

python
import os, requests
H = {"Authorization": f"Bearer {os.environ['FUNDFACTS_API_KEY']}"}
r = requests.post("https://fundfactsapi.com/api/v1/funds", json={"isins": ["IE00B4L5Y983", "IE00B3RBWM25"], "wait": True}, headers=H, timeout=300)
funds = {x["isin"]: x for x in r.json()["results"] if x["status"] == "ok"}

Put the figures side by side

python
def row(label, get):
    return [label] + [get(funds[i]) for i in ("IE00B4L5Y983", "IE00B3RBWM25")]
​
table = [
    row("Name", lambda f: f["name"]),
    row("Category", lambda f: f["data"]["profile"]["category"]),
    row("TER", lambda f: f["data"]["headlineMetrics"]["ter"]),
    row("Risk (1-7)", lambda f: f["data"]["riskRating"]),
    row("Size", lambda f: f["data"]["keyFacts"]["aum"]),
    row("Holdings", lambda f: f["data"]["keyFacts"]["holdings"]),
    row("Top 10 weight", lambda f: round(sum(h["weight"] for h in f["data"]["topHoldings"][:10]), 1)),
    row("US weight", lambda f: next((g["weight"] for g in f["data"]["geography"] if g["label"] == "United States"), None)),
    row("3y vol", lambda f: f["data"]["headlineMetrics"]["volatility3y"]),
    row("Max drawdown", lambda f: f["data"]["metrics"]["maxDrawdown"]),
    row("2025 return", lambda f: dict(zip(f["data"]["calendarReturns"]["years"], f["data"]["calendarReturns"]["fund"])).get("2025")),
    row("As of", lambda f: f["data"]["dataAsOf"]),
]
for r in table:
    print(f"{r[0]:<14} {str(r[1]):<28} {str(r[2]):<28}")

Shared holdings

bash
curl -s "https://fundfactsapi.com/api/v1/overlap?isins=IE00B4L5Y983,IE00B3RBWM25" -H "Authorization: Bearer $FUNDFACTS_API_KEY" \
  | jq '.pairs[0] | {overlap, sharedCount, top: .shared[:5]}'

overlap is the percentage of portfolio weight the two funds have in common (the sum over shared names of the smaller weight), shared lists each common holding with its weight in both. Pro and above; the free ETF overlap tool runs it for you in the browser.

Presenting it

Keep the strings as printed (a TER of "0.20%" next to "0.22%" reads better than 0.002), show dataAsOf under the table, and avoid ranking words: a comparison presents facts, not a recommendation. The comparison tool guide covers the UI and caching, and the ETF comparison website use case the SEO angle.