Trades and quotes
Event prices, sizes, conditions, venues, and sequence.
MARKET DATA LATENCY MAP
Free Market Data API: Real-Time Options
Separate reference, delayed, snapshot, streaming, and direct-feed data before choosing a provider.
Map the latency promise
Reference
End-of-day or periodic values for valuation and reporting.
Delayed
Exchange-controlled delay, often suitable for display and research.
Snapshot
Current-looking response at request time, not necessarily event-by-event.
Streaming
Incremental events with ordering, reconnect, and gap handling.
Direct feed
Venue-native data with explicit entitlement and infrastructure requirements.
Market data is a family of datasets
Bars
Windowed OHLCV with timezone and session rules.
Reference
Symbols, listings, corporate actions, and calendars.
Derivatives
Contracts, expiries, strikes, curves, and settlement.
News and events
Timestamped context with source and entity mapping.
Derived analytics
Indicators and signals whose formulas must be disclosed.
TL;DR
Best free starting point
Alpaca is practical for US stock prototypes, but its free live feed is IEX rather than the consolidated SIP.
Best multi-asset trial
Twelve Data exposes stocks, forex, crypto, ETFs, and more, while free credits and market entitlements still define usable coverage.
Best for direct-market research
Databento offers credits and direct-feed depth, but free credit is not the same as a permanent free live plan.
Core decision
Choose by venue coverage, timestamp quality, streaming limits, and legal use—not by the word free alone.
What “free” and “real-time” mean for this API
Searches for a free real-time market data API usually hide several different jobs: a watchlist that refreshes every minute, a streaming trading dashboard, a backtest downloader, or an AI agent that must cite fresh prices. One provider rarely wins all four.
The first filter is the feed, not the SDK. US equities may come from one venue such as IEX, a consolidated SIP, or a delayed feed. Options can require OPRA rights. Forex may be an indicative broker stream or a daily central-bank reference rate. Crypto is often easier to stream, but exchange fragmentation creates a different coverage problem.
For that reason, this comparison treats free as a testable commercial boundary: what is available at zero monthly cost, which fields and symbols are included, how fresh the timestamps are, and what happens when the prototype becomes a public product.
Provider access matrix
| Provider | Typical strength | Delivery | Verify |
|---|---|---|---|
| Alpaca | US equities and brokerage context | REST and streaming | Feed tier and exchange coverage |
| Finnhub | Multi-asset application data | REST and WebSocket | Plan, symbol mapping, delay |
| Twelve Data | Multi-asset bars and indicators | REST and WebSocket | Credits and streaming limits |
| Databento | Normalized institutional datasets | Historical and live | Dataset license, schema, venue |
| FMP in QVeris | Application-oriented financial data | Inspectable capability | Provider contract and timestamps |
Provider comparison: access, fields, and limits
| Provider | Zero-cost access | Real-time scope | Best use |
|---|---|---|---|
| Alpaca | Permanent free market-data plan | Live IEX stocks; limited symbols over WebSocket; indicative options | US equity prototypes and paper trading |
| Finnhub | Free personal-use plan | Stocks, forex, crypto; plan and exchange details vary | Multi-asset prototypes |
| Twelve Data | Basic free plan with credits | Broad assets; full WebSocket and international access depend on plan | Broad symbol discovery and REST testing |
| Databento | Signup credits | Direct feeds and granular schemas; live use is subscription/licensing sensitive | Market microstructure evaluation |
Free tiers, prices, limits, and licenses change. Treat this as a decision framework and verify current official terms before production use.
The fields that decide whether the data is usable
Freshness
Measure source timestamp, provider receive time, and application receive time separately. A fast API can still return delayed market events.
Venue completeness
A live single-venue feed is real-time but not a consolidated view. That distinction affects quotes, volume, highs, lows, and alerts.
Streaming capacity
Check concurrent connections, subscribed symbols, reconnect rules, heartbeats, and whether snapshots must be loaded before deltas.
Usage rights
Personal research, internal non-display use, public display, redistribution, and derived analytics can require different terms.
Which option fits your workload?
Learning and paper trading
Start with Alpaca or another clearly documented limited live feed. Prioritize simple authentication, snapshots plus WebSocket updates, and reproducible reconnect behavior.
Multi-asset dashboard
Favor a unified provider such as Finnhub or Twelve Data, then verify every exchange and asset class separately. A single API surface does not guarantee equal freshness everywhere.
Public customer product
Begin with licensing and display rights before latency. Estimate users, symbol fan-out, derived-data rules, attribution, exchange fees, and redistribution terms.
Research agent
Use timestamped snapshots unless the task truly needs streaming. Require the agent to return provider, feed, event time, retrieval time, market session, and units with every answer.
Normalize without erasing evidence
- 01
Ingest raw
Keep the provider payload and request identifiers.
- 02
Attach clocks
Store event, provider, receipt, and normalization times.
- 03
Map identity
Resolve venue, symbol, asset class, currency, and corporate actions.
- 04
Normalize
Create a stable internal record without discarding source fields.
- 05
Monitor
Measure freshness, gaps, duplicates, corrections, and entitlement errors.
A practical evaluation and implementation playbook
Build a ten-symbol truth set
Mix liquid and illiquid securities across open, pre-market, after-hours, and halted conditions. Compare source timestamps against an independent reference.
Test REST and stream together
Use REST for the initial snapshot and WebSocket for updates. Confirm sequence handling, duplicates, late messages, and reconnect recovery.
Price the first production month
Model symbol count, users, calls, egress, exchange fees, display rights, and historical downloads. Free-plan limits often fail on a different dimension than request count.
Keep a provider adapter
Normalize timestamps, symbols, corporate actions, conditions, and error states behind your own interface so changing feeds does not rewrite the product.
Provider-by-provider notes: where the free tier stops
Alpaca: live does not mean consolidated
Alpaca is one of the clearest free starting points for US equities because its documentation states the feed boundary: the free plan streams live IEX data, while consolidated SIP coverage belongs to the paid tier. That makes it useful for paper trading, alert prototypes, and learning event-driven architecture, but a poor benchmark for total-market volume or best quotes across every venue.
Finnhub: broad coverage with plan-sensitive detail
Finnhub combines stocks, forex, crypto, company news, and fundamentals behind one key. The convenience is valuable for a multi-asset proof of concept, but teams should test the exact exchanges, symbols, history, and personal-use terms they need. A provider can advertise real-time access while individual venues or redistribution scenarios remain restricted.
Twelve Data: useful unified schema
Twelve Data is attractive when developers want a common REST schema across global symbols and asset classes. Its credit model makes endpoint experimentation easy, but production capacity depends on how one request consumes credits, which markets are included, and whether the workload needs full WebSocket access. Price a representative watchlist rather than extrapolating from a one-symbol demo.
Databento: evaluation credit, not a forever-free feed
Databento is strongest when the question is data fidelity: direct feeds, granular schemas, market-by-order depth, precise timestamps, and licensing visibility. Signup credit helps evaluate historical data and offset a subscription, but it should be modeled as an evaluation budget rather than a permanent zero-cost production feed.
Common mistakes that make a free API expensive
Treating API latency as data latency
A 50 ms response does not prove the quote itself is current.
Ignoring market sessions
Pre-market, after-hours, holidays, halts, and half days must be represented explicitly.
Shipping with prototype rights
A plan permitted for personal testing may not allow customer-facing display or redistribution.
Using one last price everywhere
Quotes, trades, midpoints, indicative values, and official closes answer different questions.
Inspect market-data capabilities
Use QVeris to inspect candidate schemas and calling requirements while preserving the underlying provider's license and provenance. Continue with FMP market-data provider details, then confirm the calling contract in the QVeris REST API reference.
FAQ
Is there a completely free real-time market data API?
Yes for limited scopes, such as a single venue, restricted symbols, personal use, or selected asset classes. Full consolidated and redistributable feeds usually introduce fees or agreements.
Is IEX data real-time?
Yes, it is live data from IEX. It is not the same as the consolidated US equity SIP covering all exchanges.
Should an AI agent use WebSocket data?
Only when the task needs event-driven freshness. Many research questions are better served by a timestamped snapshot with provenance.
How do I compare free tiers fairly?
Use the same symbols, sessions, request pattern, and output checks, then compare legal use and upgrade cost separately from technical performance.