The short answer

For backtesting data in 2026, Alpaca free IEX plus Tiingo ($10/mo) is the cheap daily-resolution default, Polygon.io flat files are the flat-rate workhorse for minute-to-tick history, Databento is the only realistic tick and order-book source at retail, and Nasdaq Data Link has a strong free fundamentals tier. Survivorship and look-ahead bias decide whether any of it means anything.

For backtesting data in 2026, the cheapest source that does not poison your results wins, and most retail backtests are wrong because of the data, not the strategy. Alpaca's free IEX feed plus Tiingo ($10/mo) is the zero-to-cheap default for daily-resolution research, with one big caveat (IEX is a fraction of consolidated volume). Polygon.io flat files are the flat-rate workhorse for minute-to-tick history. Databento is the only realistic route to tick and order-book history at retail scale, billed by data volume. Nasdaq Data Link carries a strong free tier for fundamentals and alternative data. Whatever you choose, the survivorship and look-ahead traps below decide whether the backtest means anything. Price the standalone-vendor route in the Data-Vendor TCO Calculator.

The data decides the backtest, not the strategy

Three data defects invalidate more retail backtests than any modeling error:

  • Survivorship bias. A dataset that only contains today's listed symbols silently drops every company that delisted, merged, or went bankrupt. Backtesting a long-equity strategy on a survivor-only universe inflates returns because the losers are gone. You need point-in-time constituents.
  • Look-ahead bias. Using data that was not yet available at the decision timestamp (restated fundamentals, end-of-day prices for an intraday decision) leaks the future into the past. Restated financials are the classic offender; you need as-reported, point-in-time fundamentals.
  • Partial-tape sampling. A feed that covers a sliver of volume (IEX is roughly 2-5% of the consolidated tape) produces prices that look real but are not the prices a SIP-tape strategy would have transacted at.

This roundup ranks sources on published pricing, documented coverage, and which of these traps each one helps or hurts. No backtest result is asserted; the survivorship and look-ahead points are structural facts about data shape, not a study we ran.

The headline table

All figures are vendor list prices and documented coverage, verified 2026-05-25 on the pages in Sources.

Source Resolution History Cheapest entry Survivorship-safe?
Alpaca (free IEX) daily, minute multi-year $0 partial tape only
Tiingo daily, minute long EOD + fundamentals $10/mo Starter needs point-in-time check
Polygon.io flat files minute → tick 15+ years $199/mo (Stocks Advanced) full SIP tape
Databento daily → L2/tick full usage-based ($199/mo Standard) full tape, point-in-time
Nasdaq Data Link daily + alt data 10+ years (premium feeds) free tier + a la carte depends on dataset

Verify on the vendor page before committing; backtest data terms and history depth change between tiers.

Who wins for which backtest

Profile: daily-resolution idea generation, zero budget

Alpaca free IEX + Tiingo Starter ($10/mo) for fundamentals. Total $10/mo, the cheapest credible starting point for directional, daily-bar research. The hard caveat: IEX is a partial tape, so any result that depends on exact fills or intraday microstructure is not trustworthy on this data. Fine for "does this signal have any edge at all," not for "what would this have returned." Promote to the SIP tape before you believe a number.

Profile: minute-to-tick history at a predictable flat rate

Polygon.io (now Massive) flat files on Stocks Advanced ($199/mo): the full SIP tape, 15+ years of history, downloadable as flat files for fast local backtesting. Flat-rate billing means a speculative re-run does not surprise you on the invoice, which is the practical edge over metered vendors for iterative research. See Polygon.io Pricing 2026.

Profile: tick and order-book history at retail scale

Databento. The realistic route to tick + L2 history, under usage-based pricing (pay per GB on uncompressed binary size), with a $199/mo Standard plan and $125 in free credits for new signups for historical pulls. Budget carefully: metered billing punishes speculative re-queries, so pull once and cache locally. See Databento vs Polygon.io 2026.

Profile: fundamentals and alternative data, low budget

Nasdaq Data Link (formerly Quandl). A strong free tier of open datasets from central banks, governments, and publishers, plus premium feeds sold a la carte with no extra charge for API access on top of the data subscription. Good for fundamentals and macro overlays; for point-in-time fundamentals, confirm the specific dataset is as-reported, not restated.

The synthetic-data alternative

When you do not have enough history, or you want to stress a strategy against regimes the tape never produced, synthetic data is the answer, not more curve-fitting on the same 10 years. The Synthetic Market Data Generator produces price paths you can backtest against, and Synthetic Data: GARCH vs GBM covers which generator matches which assumption. This is also how you avoid overfitting a single historical path, which the Backtest Overfitting Score measures.

Validation matters more than the vendor

A clean data source feeding an overfit validation procedure still produces a fiction. Whatever vendor you pick, the backtest is only as good as the walk-forward discipline around it. See Walk-Forward Validation Cookbook and Did You Overfit? PBO and Deflated Sharpe before you trust any equity curve.

Price the standalone route

If you want a data feed not tied to your broker, the Data-Vendor TCO Calculator ranks the vendors for your scenario. The verified output block below is computed live from that engine for a live, options-included, no-futures profile; flip the inputs to match your universe and resolution before subscribing.

Connects to

Sources

Editorial independence

AI Fin Hub Research maintains editorial independence across sponsor relationships. Vendor placements in tools and comparators are not altered by sponsor payments. Disclosures at /sponsor-disclosure/.

Verified engine output

Show the recompute-verified inputs and outputs
Backtest data feed: live data and options coverage required, no futures
Inputs
needs_livetrue
needs_optionstrue
needs_futuresfalse
Result
scenario › universemedium
scenario › resolutionminute
scenario › history5-year
scenario › needs livetrue
scenario › needs optionstrue
scenario › needs futuresfalse
ranked › row 1 › vendor › idalpaca
ranked › row 1 › vendor › nameAlpaca Markets
ranked › row 1 › vendor › urlhttps://alpaca.markets
ranked › row 1 › vendor › short pitchBroker-bundled market data. Generous free tier via IEX feed; SIP feed requires paid plan.
ranked › row 1 › vendor › has overagefalse
ranked › row 1 › vendor › last checked2026-05-25
ranked › row 1 › vendor › tiers › row 1 › nameFree (IEX feed)
ranked › row 1 › vendor › tiers › row 1 › monthly0
ranked › row 1 › vendor › tiers › row 1 › includes livetrue
ranked › row 1 › vendor › tiers › row 1 › includes optionsfalse
ranked › row 1 › vendor › tiers › row 1 › includes futuresfalse
ranked › row 1 › vendor › tiers › row 1 › resolutions › row 1daily
ranked › row 1 › vendor › tiers › row 1 › resolutions › row 2minute
ranked › row 1 › vendor › tiers › row 1 › notes › row 1IEX feed only (subset of volume)
ranked › row 1 › vendor › tiers › row 1 › notes › row 2Free with Alpaca brokerage account
ranked › row 1 › vendor › tiers › row 2 › nameAlgo Trader Plus (SIP feed)
ranked › row 1 › vendor › tiers › row 2 › monthly99
ranked › row 1 › vendor › tiers › row 2 › includes livetrue
ranked › row 1 › vendor › tiers › row 2 › includes optionstrue
ranked › row 1 › vendor › tiers › row 2 › includes futuresfalse
ranked › row 1 › vendor › tiers › row 2 › resolutions › row 1daily
ranked › row 1 › vendor › tiers › row 2 › resolutions › row 2minute
ranked › row 1 › vendor › tiers › row 2 › resolutions › row 3second
ranked › row 1 › vendor › tiers › row 2 › resolutions › row 4tick
ranked › row 1 › vendor › tiers › row 2 › notes › row 1Full SIP consolidated tape
ranked › row 1 › vendor › tiers › row 2 › notes › row 2Options chains included
ranked › row 1 › tier › nameAlgo Trader Plus (SIP feed)
ranked › row 1 › tier › monthly99
ranked › row 1 › tier › includes livetrue
ranked › row 1 › tier › includes optionstrue
ranked › row 1 › tier › includes futuresfalse
ranked › row 1 › tier › resolutions › row 1daily
ranked › row 1 › tier › resolutions › row 2minute
ranked › row 1 › tier › resolutions › row 3second
ranked › row 1 › tier › resolutions › row 4tick
ranked › row 1 › tier › notes › row 1Full SIP consolidated tape
ranked › row 1 › tier › notes › row 2Options chains included
ranked › row 1 › monthly99
ranked › row 1 › one time0
ranked › row 1 › annual total1188
ranked › row 1 › meets resolutiontrue
ranked › row 1 › meets livetrue
ranked › row 1 › meets optionstrue
ranked › row 1 › meets futurestrue
ranked › row 1 › meets alltrue
ranked › row 2 › vendor › idtiingo
ranked › row 2 › vendor › nameTiingo
ranked › row 2 › vendor › urlhttps://www.tiingo.com
ranked › row 2 › vendor › short pitchStrong fundamentals + EOD pricing at low cost. Limited intraday. Favorite for long-horizon research.
ranked › row 2 › vendor › has overagefalse
ranked › row 2 › vendor › last checked2026-04-20
ranked › row 2 › vendor › tiers › row 1 › nameTiingo Starter
ranked › row 2 › vendor › tiers › row 1 › monthly10
ranked › row 2 › vendor › tiers › row 1 › includes livefalse
ranked › row 2 › vendor › tiers › row 1 › includes optionsfalse
ranked › row 2 › vendor › tiers › row 1 › includes futuresfalse
ranked › row 2 › vendor › tiers › row 1 › resolutions › row 1daily
ranked › row 2 › vendor › tiers › row 1 › notes › row 1EOD equities
ranked › row 2 › vendor › tiers › row 1 › notes › row 2News API included
ranked › row 2 › vendor › tiers › row 1 › notes › row 3Price unconfirmed 2026-05-25 — official pricing page not machine-readable
ranked › row 2 › vendor › tiers › row 2 › nameTiingo Power
ranked › row 2 › vendor › tiers › row 2 › monthly50
ranked › row 2 › vendor › tiers › row 2 › includes livefalse
ranked › row 2 › vendor › tiers › row 2 › includes optionsfalse
ranked › row 2 › vendor › tiers › row 2 › includes futuresfalse
ranked › row 2 › vendor › tiers › row 2 › resolutions › row 1daily
ranked › row 2 › vendor › tiers › row 2 › resolutions › row 2minute
ranked › row 2 › vendor › tiers › row 2 › notes › row 1Intraday bars
ranked › row 2 › vendor › tiers › row 2 › notes › row 2Crypto data
ranked › row 2 › vendor › tiers › row 2 › notes › row 3Fundamentals included
ranked › row 2 › tier › nameTiingo Starter
ranked › row 2 › tier › monthly10
ranked › row 2 › tier › includes livefalse
ranked › row 2 › tier › includes optionsfalse
ranked › row 2 › tier › includes futuresfalse
ranked › row 2 › tier › resolutions › row 1daily
ranked › row 2 › tier › notes › row 1EOD equities
ranked › row 2 › tier › notes › row 2News API included
ranked › row 2 › tier › notes › row 3Price unconfirmed 2026-05-25 — official pricing page not machine-readable
ranked › row 2 › monthly10
ranked › row 2 › one time0
ranked › row 2 › annual total120
ranked › row 2 › meets resolutionfalse
ranked › row 2 › meets livefalse
ranked › row 2 › meets optionsfalse
ranked › row 2 › meets futurestrue
ranked › row 2 › meets allfalse
ranked › row 3 › vendor › idfmp
ranked › row 3 › vendor › nameFinancial Modeling Prep
ranked › row 3 › vendor › urlhttps://site.financialmodelingprep.com
ranked › row 3 › vendor › short pitchFundamentals-heavy. Earnings, filings, transcripts. Price data is a secondary offer.
ranked › row 3 › vendor › has overagefalse
ranked › row 3 › vendor › last checked2026-04-20
ranked › row 3 › vendor › tiers › row 1 › nameStarter
ranked › row 3 › vendor › tiers › row 1 › monthly14
ranked › row 3 › vendor › tiers › row 1 › includes livefalse
ranked › row 3 › vendor › tiers › row 1 › includes optionsfalse
ranked › row 3 › vendor › tiers › row 1 › includes futuresfalse
ranked › row 3 › vendor › tiers › row 1 › resolutions › row 1daily
ranked › row 3 › vendor › tiers › row 1 › notes › row 15 years history
ranked › row 3 › vendor › tiers › row 1 › notes › row 2250 API calls/day
ranked › row 3 › vendor › tiers › row 1 › notes › row 3Price unconfirmed 2026-05-25 — FMP list prices not consistently published
ranked › row 3 › vendor › tiers › row 2 › namePremium
ranked › row 3 › vendor › tiers › row 2 › monthly29
ranked › row 3 › vendor › tiers › row 2 › includes livefalse
ranked › row 3 › vendor › tiers › row 2 › includes optionsfalse
ranked › row 3 › vendor › tiers › row 2 › includes futuresfalse
ranked › row 3 › vendor › tiers › row 2 › resolutions › row 1daily
ranked › row 3 › vendor › tiers › row 2 › resolutions › row 2minute
ranked › row 3 › vendor › tiers › row 2 › notes › row 1Full history
ranked › row 3 › vendor › tiers › row 2 › notes › row 2750 calls/day
ranked › row 3 › vendor › tiers › row 3 › nameUltimate
ranked › row 3 › vendor › tiers › row 3 › monthly79
ranked › row 3 › vendor › tiers › row 3 › includes livetrue
ranked › row 3 › vendor › tiers › row 3 › includes optionsfalse
ranked › row 3 › vendor › tiers › row 3 › includes futuresfalse
ranked › row 3 › vendor › tiers › row 3 › resolutions › row 1daily
ranked › row 3 › vendor › tiers › row 3 › resolutions › row 2minute
ranked › row 3 › vendor › tiers › row 3 › resolutions › row 3second
ranked › row 3 › vendor › tiers › row 3 › notes › row 1Real-time
ranked › row 3 › vendor › tiers › row 3 › notes › row 2Unlimited calls
ranked › row 3 › tier › nameStarter
ranked › row 3 › tier › monthly14
ranked › row 3 › tier › includes livefalse
ranked › row 3 › tier › includes optionsfalse
ranked › row 3 › tier › includes futuresfalse
ranked › row 3 › tier › resolutions › row 1daily
ranked › row 3 › tier › notes › row 15 years history
ranked › row 3 › tier › notes › row 2250 API calls/day
ranked › row 3 › tier › notes › row 3Price unconfirmed 2026-05-25 — FMP list prices not consistently published
ranked › row 3 › monthly14
ranked › row 3 › one time0
ranked › row 3 › annual total168
ranked › row 3 › meets resolutionfalse
ranked › row 3 › meets livefalse
ranked › row 3 › meets optionsfalse
ranked › row 3 › meets futurestrue
ranked › row 3 › meets allfalse
ranked › row 4 › vendor › idpolygon
ranked › row 4 › vendor › namePolygon.io
ranked › row 4 › vendor › urlhttps://polygon.io
ranked › row 4 › vendor › short pitchFlat-rate subscription. Real-time + historical for US equities. Popular retail default.
ranked › row 4 › vendor › has overagefalse
ranked › row 4 › vendor › last checked2026-05-25
ranked › row 4 › vendor › tiers › row 1 › nameStocks Starter
ranked › row 4 › vendor › tiers › row 1 › monthly29
ranked › row 4 › vendor › tiers › row 1 › includes livefalse
ranked › row 4 › vendor › tiers › row 1 › includes optionsfalse
ranked › row 4 › vendor › tiers › row 1 › includes futuresfalse
ranked › row 4 › vendor › tiers › row 1 › resolutions › row 1daily
ranked › row 4 › vendor › tiers › row 1 › resolutions › row 2minute
ranked › row 4 › vendor › tiers › row 1 › notes › row 115-min delayed market data
ranked › row 4 › vendor › tiers › row 1 › notes › row 25 calls/min
ranked › row 4 › vendor › tiers › row 2 › nameStocks Developer
ranked › row 4 › vendor › tiers › row 2 › monthly79
ranked › row 4 › vendor › tiers › row 2 › includes livefalse
ranked › row 4 › vendor › tiers › row 2 › includes optionsfalse
ranked › row 4 › vendor › tiers › row 2 › includes futuresfalse
ranked › row 4 › vendor › tiers › row 2 › resolutions › row 1daily
ranked › row 4 › vendor › tiers › row 2 › resolutions › row 2minute
ranked › row 4 › vendor › tiers › row 2 › resolutions › row 3second
ranked › row 4 › vendor › tiers › row 2 › notes › row 115-min delayed
ranked › row 4 › vendor › tiers › row 2 › notes › row 2Unlimited API calls
ranked › row 4 › vendor › tiers › row 3 › nameStocks Advanced
ranked › row 4 › vendor › tiers › row 3 › monthly199
ranked › row 4 › vendor › tiers › row 3 › includes livetrue
ranked › row 4 › vendor › tiers › row 3 › includes optionsfalse
ranked › row 4 › vendor › tiers › row 3 › includes futuresfalse
ranked › row 4 › vendor › tiers › row 3 › resolutions › row 1daily
ranked › row 4 › vendor › tiers › row 3 › resolutions › row 2minute
ranked › row 4 › vendor › tiers › row 3 › resolutions › row 3second
ranked › row 4 › vendor › tiers › row 3 › resolutions › row 4tick
ranked › row 4 › vendor › tiers › row 3 › notes › row 1Full real-time
ranked › row 4 › vendor › tiers › row 3 › notes › row 2Unlimited API calls
ranked › row 4 › tier › nameStocks Starter
ranked › row 4 › tier › monthly29
ranked › row 4 › tier › includes livefalse
ranked › row 4 › tier › includes optionsfalse
ranked › row 4 › tier › includes futuresfalse
ranked › row 4 › tier › resolutions › row 1daily
ranked › row 4 › tier › resolutions › row 2minute
ranked › row 4 › tier › notes › row 115-min delayed market data
ranked › row 4 › tier › notes › row 25 calls/min
ranked › row 4 › monthly29
ranked › row 4 › one time0
ranked › row 4 › annual total348
ranked › row 4 › meets resolutiontrue
ranked › row 4 › meets livefalse
ranked › row 4 › meets optionsfalse
ranked › row 4 › meets futurestrue
ranked › row 4 › meets allfalse
ranked › row 5 › vendor › idalpha-vantage
ranked › row 5 › vendor › nameAlpha Vantage
ranked › row 5 › vendor › urlhttps://www.alphavantage.co
ranked › row 5 › vendor › short pitchBudget tier with broad coverage. Rate limits tight. Workable for low-frequency research.
ranked › row 5 › vendor › has overagefalse
ranked › row 5 › vendor › last checked2026-05-25
ranked › row 5 › vendor › tiers › row 1 › namePremium 75
ranked › row 5 › vendor › tiers › row 1 › monthly49.99
ranked › row 5 › vendor › tiers › row 1 › includes livefalse
ranked › row 5 › vendor › tiers › row 1 › includes optionsfalse
ranked › row 5 › vendor › tiers › row 1 › includes futuresfalse
ranked › row 5 › vendor › tiers › row 1 › resolutions › row 1daily
ranked › row 5 › vendor › tiers › row 1 › resolutions › row 2minute
ranked › row 5 › vendor › tiers › row 1 › notes › row 175 calls/min, no daily limit
ranked › row 5 › vendor › tiers › row 1 › notes › row 2Free key capped at 25 calls/day, 5/min
ranked › row 5 › vendor › tiers › row 2 › namePremium 1200
ranked › row 5 › vendor › tiers › row 2 › monthly249.99
ranked › row 5 › vendor › tiers › row 2 › includes livefalse
ranked › row 5 › vendor › tiers › row 2 › includes optionsfalse
ranked › row 5 › vendor › tiers › row 2 › includes futuresfalse
ranked › row 5 › vendor › tiers › row 2 › resolutions › row 1daily
ranked › row 5 › vendor › tiers › row 2 › resolutions › row 2minute
ranked › row 5 › vendor › tiers › row 2 › resolutions › row 3second
ranked › row 5 › vendor › tiers › row 2 › notes › row 11,200 calls/min, no daily limit
ranked › row 5 › vendor › tiers › row 2 › notes › row 2Rate-tiered ladder: $99.99/150, $149.99/300, $199.99/600, $249.99/1200
ranked › row 5 › tier › namePremium 75
ranked › row 5 › tier › monthly49.99
ranked › row 5 › tier › includes livefalse
ranked › row 5 › tier › includes optionsfalse
ranked › row 5 › tier › includes futuresfalse
ranked › row 5 › tier › resolutions › row 1daily
ranked › row 5 › tier › resolutions › row 2minute
ranked › row 5 › tier › notes › row 175 calls/min, no daily limit
ranked › row 5 › tier › notes › row 2Free key capped at 25 calls/day, 5/min
ranked › row 5 › monthly49.99
ranked › row 5 › one time0
ranked › row 5 › annual total599.88
ranked › row 5 › meets resolutiontrue
ranked › row 5 › meets livefalse
ranked › row 5 › meets optionsfalse
ranked › row 5 › meets futurestrue
ranked › row 5 › meets allfalse
ranked › row 6 › vendor › iddatabento
ranked › row 6 › vendor › nameDatabento
ranked › row 6 › vendor › urlhttps://databento.com
ranked › row 6 › vendor › short pitchPer-unit metered pricing. Strong for institutional-quality tick + L2 data. No subscriptions on base offer.
ranked › row 6 › vendor › has overagetrue
ranked › row 6 › vendor › last checked2026-05-25
ranked › row 6 › vendor › tiers › row 1 › nameDatabento metered (typical retail)
ranked › row 6 › vendor › tiers › row 1 › monthly125
ranked › row 6 › vendor › tiers › row 1 › includes livetrue
ranked › row 6 › vendor › tiers › row 1 › includes optionsfalse
ranked › row 6 › vendor › tiers › row 1 › includes futurestrue
ranked › row 6 › vendor › tiers › row 1 › resolutions › row 1daily
ranked › row 6 › vendor › tiers › row 1 › resolutions › row 2minute
ranked › row 6 › vendor › tiers › row 1 › resolutions › row 3second
ranked › row 6 › vendor › tiers › row 1 › resolutions › row 4tick
ranked › row 6 › vendor › tiers › row 1 › resolutions › row 5level2
ranked › row 6 › vendor › tiers › row 1 › notes › row 1Usage-metered: historical is pay-as-you-go priced per GB (uncompressed binary), no subscription required; $125 free credits on signup
ranked › row 6 › vendor › tiers › row 1 › notes › row 2Subscription option: Standard $199/mo (historical core schemas + 1yr L1 / 1mo L2-L3); $125/mo modeled typical retail metered spend
ranked › row 6 › vendor › tiers › row 1 › notes › row 3Live data + dedicated support on Plus ($1,399/mo, annual); Unlimited $3,500/mo (verified 2026-05-25)
ranked › row 6 › vendor › tiers › row 1 › notes › row 4Per-GB cost scales aggressively with universe and resolution
ranked › row 6 › tier › nameDatabento metered (typical retail)
ranked › row 6 › tier › monthly125
ranked › row 6 › tier › includes livetrue
ranked › row 6 › tier › includes optionsfalse
ranked › row 6 › tier › includes futurestrue
ranked › row 6 › tier › resolutions › row 1daily
ranked › row 6 › tier › resolutions › row 2minute
ranked › row 6 › tier › resolutions › row 3second
ranked › row 6 › tier › resolutions › row 4tick
ranked › row 6 › tier › resolutions › row 5level2
ranked › row 6 › tier › notes › row 1Usage-metered: historical is pay-as-you-go priced per GB (uncompressed binary), no subscription required; $125 free credits on signup
ranked › row 6 › tier › notes › row 2Subscription option: Standard $199/mo (historical core schemas + 1yr L1 / 1mo L2-L3); $125/mo modeled typical retail metered spend
ranked › row 6 › tier › notes › row 3Live data + dedicated support on Plus ($1,399/mo, annual); Unlimited $3,500/mo (verified 2026-05-25)
ranked › row 6 › tier › notes › row 4Per-GB cost scales aggressively with universe and resolution
ranked › row 6 › monthly125
ranked › row 6 › one time0
ranked › row 6 › annual total1500
ranked › row 6 › meets resolutiontrue
ranked › row 6 › meets livetrue
ranked › row 6 › meets optionsfalse
ranked › row 6 › meets futurestrue
ranked › row 6 › meets allfalse

Computed live at build time.

Frequently asked questions

What is the cheapest backtesting data source in 2026?
Alpaca's free IEX feed plus Tiingo Starter ($10/mo) for fundamentals, $10/mo all in. The caveat is decisive: IEX is roughly 2-5% of the consolidated tape, fine for daily-bar idea generation but not for any result depending on exact fills or intraday microstructure. Move to the full SIP tape before trusting a return number.
Which data source avoids survivorship bias for equity backtests?
Whichever gives you point-in-time index constituents that still contain delisted and merged names. Full-tape vendors like Polygon and Databento carry the complete universe; a survivor-only dataset quietly drops the losers and inflates returns. For fundamentals, confirm the dataset is as-reported, not restated, or you reintroduce look-ahead bias.
When should I use synthetic data instead of historical data?
When history is too short to test a strategy, or when you want to stress it against regimes the tape never produced. Synthetic generation also breaks the habit of overfitting one historical path. Use the Synthetic Market Data Generator, then check the result with the Backtest Overfitting Score.