Comparison · Trading
Two of these three publish a real trading API for stocks. The third does not, and the popular libraries that pretend otherwise are reverse-engineered from a private app API, violate the terms of service, and get accounts restricted. That is the whole comparison in one paragraph, but the details of the other two matter a lot.
Disclosure and scope: I build my own trading tools and I have written adapters for more than one of these brokers, including one I later labelled a mistake in my own documentation for exactly the reason described below. I have no affiliate or sponsorship relationship with any broker on this page. Nothing here is investment advice, none of it is a recommendation to trade, and no claim about profitability appears anywhere on this page.
Before comparing latency or order types, ask a much blunter question: does this broker publish a documented API that its terms of service permit you to use for automated trading of the instrument you care about?
Alpaca: yes, that is the entire product. Interactive Brokers: yes, several of them, and it has published trading APIs for longer than most retail traders have been alive. Robinhood: no official public API for retail equities. It does publish an official crypto trading API with proper API-key authentication, which is a supported path for crypto and only crypto. Everything you have seen for automating Robinhood stock orders is a community library that reverse-engineers the private endpoints the mobile and web apps use.
This deserves its own section because it is the most common mistake in retail algo trading and the consequences land on your actual brokerage account.
The recommendation is unambiguous: use an official API. If you want Robinhood specifically, the supported path is their published crypto trading API, and equities automation is not available to you there. If you want to automate stocks, that is what Alpaca and Interactive Brokers are for. I say this having written a reverse-engineered equities adapter myself and then flagged it in my own project notes as the wrong default, which is a slower way to learn the same lesson.
| Alpaca | Interactive Brokers | Robinhood | |
|---|---|---|---|
| Official equities API | Yes, REST plus streaming, documented and versioned | Yes, TWS socket API, Client Portal Web API, and FIX for institutional | No. Unofficial libraries only, against the terms of service |
| Official crypto API | Yes | Crypto available through the same account structure | Yes, key-authenticated, the one supported programmatic path |
| Real paper trading | Yes, same endpoints and same SDK, you change the base URL and the keys | Yes, a full paper account alongside the live one | None. Production or nothing |
| Setup to first order | API keys, an SDK install, a few lines | Install Trader Workstation or IB Gateway, keep the process running, connect over a socket, usually via a community wrapper | n/a |
| Always-on architecture | Cloud API, nothing to run locally | A local gateway process must stay up and expects a scheduled daily restart | n/a |
| Instrument coverage | US equities, ETFs, options, crypto. Check current product coverage before assuming anything else | The widest here by a distance: global equities, options, futures, forex, bonds, funds, many exchanges | n/a for automation |
| Market data | Free tier is IEX only, a single venue and a small share of consolidated volume. Full consolidated data is a paid subscription | Paid subscriptions per exchange, and you generally need them for anything serious | n/a |
| Commissions | Commission-free US equities and ETFs | A commission-free tier for US stocks and a professional tier with commissions and smart order routing | Commission-free |
| Rate limits | Documented per-key limits | Message pacing limits that will bite you, plus historical-data pacing violations | n/a |
| Client libraries | First-party SDKs including Python | Official API plus widely used community wrappers | Unofficial only |
| Learning curve | Low | High | n/a |
| Best fit | A first automated strategy, or anything cloud-native | Anything needing futures, forex, options complexity or non-US markets | Manual trading, or crypto through the official API |
Alpaca was built API-first, and the structural advantage that matters most is that paper and live are the same interface. You point at a different base URL with a different key pair and everything else in your code is identical. That means the thing you tested is the thing you deploy, which removes an entire category of bug that exists in setups where the simulator and the broker are different codepaths.
The friction cost is genuinely low: create keys, install the SDK, place an order. Bracket and one-cancels-other orders are supported, which covers the entry-with-stop-and-target pattern most swing strategies need, and fractional and notional orders make position sizing on a small account straightforward.
Where Alpaca loses. The free market-data tier is IEX only. IEX is one venue and carries a small fraction of consolidated US volume, so the free feed is fine for learning and for slow strategies on liquid names, and quietly wrong for anything sensitive to the actual national best bid and offer. Full consolidated data is a paid subscription, and pretending otherwise is how backtests end up unreproducible. Instrument coverage is narrower than IBKR, order-type support is simpler, and it is a younger broker than the alternative, with the outage history any broker has. If your strategy needs futures, forex, or a market outside the US, this is the wrong tool.
IBKR is what you use when the instrument list decides the question. Global equities, options with real complexity, futures, forex, bonds: it is all in one account with one API surface, and there is no retail competitor close to it on breadth. It also gives you a full paper account that mirrors the live one, which for years was the only free realistic simulator available to a retail developer.
Where IBKR loses, and it loses hard on developer experience. The classic TWS API is not a web API. It expects a local Trader Workstation or IB Gateway process to be running and logged in, you connect to it over a socket, and the connection expects a scheduled daily restart. Most people do not use the raw API at all, they use a community Python wrapper, which is excellent and is also a third-party layer between you and your broker. There are message pacing limits and historical-data pacing violations that are easy to trip and produce confusing failures rather than clean errors. Market data is a per-exchange paid subscription, so the true monthly cost is not the commission schedule, it is the data. And onboarding is heavier than the alternative in every respect, including account approval.
The compensation is that once it works, it works at a scale and breadth nothing else here matches, and that professional-tier routing is a genuinely different execution product from commission-free retail order handling.
Robinhood is a good manual trading app with a clean interface and no commissions, and none of that is in dispute. The problem is narrow and total: there is no sanctioned way to automate equities on it. The official crypto trading API is real and supported and is the correct choice if crypto is what you want to automate on Robinhood. For stocks, the only options are manual entry or a terms-of-service violation, and the second one is not an option.
Also worth stating plainly: "commission-free" is not the same as "free". Retail brokers monetise order flow and spread. That cost is invisible on your statement and real in your fills, and it is one reason execution-sensitive strategies migrate to professional-tier routing even though the commission line item goes up.
Both Alpaca and IBKR give you a real paper environment, which is the single most important feature in this comparison for anyone who has not run an automated strategy before. Use it. But understand what it does not model.
The rule I hold myself to, written into the promotion gate in my own trading code, is a fixed number of closed paper trades with positive realised expectancy before a live broker key is even installed. The number matters less than the fact that it is decided in advance, in writing, by someone who is not currently watching a position. The reasoning is in going from paper to live trading, and the statistical case for not trusting a small sample is in walk-forward backtesting.
For an automated strategy the recurring costs usually rank in this order, and commissions are rarely first.
This is your first automated strategy, you are trading US equities or ETFs, and you want paper and live to be the same code with a different key. Budget for the paid data tier the moment your strategy becomes sensitive to the actual spread, and do not let the free IEX feed silently define your backtest universe.
You need futures, forex, options structures, or markets outside the US, or you care about execution quality enough to pay for professional routing. Accept that you are buying breadth at the cost of a gateway process, a community wrapper, pacing limits and a heavier onboarding, and budget for per-exchange data.
You are trading manually, or you specifically want to automate crypto through the official key-authenticated API. Do not automate equities there. There is no supported path, and the unsupported path risks the account itself.
Nothing stops you from developing against Alpaca's paper environment for the fast iteration loop and running production on IBKR for the instrument coverage. The abstraction cost is one adapter interface, and writing that interface early is cheaper than writing it after your strategy is entangled with one broker's order model. That is how my own execution tooling is structured, and the screener side is deliberately broker-agnostic for the same reason.
Alpaca if you are starting. IBKR if you have outgrown US equities or need real execution control. Robinhood for crypto through the official API, or for tapping buttons with your thumb. And whichever you pick, the API is the least interesting part of the problem: the hard part is having something worth automating, which is a question about expectancy and sample size rather than about REST endpoints. R-multiples and expectancy is the arithmetic that decides whether any of this is worth wiring up at all.
FAQ
Robinhood publishes an official crypto trading API with key-based authentication, which is a supported path for automating crypto. It does not publish a public API for retail equities. The community libraries that automate Robinhood stock orders reverse-engineer the private endpoints its own apps use, which violates the terms of service and can get an account restricted or closed.
No. Beyond violating the terms of service, these libraries talk to production with no paper mode, so an integration bug is a real order in a real account. They typically require storing your password and multi-factor seed on disk, and they break without warning whenever the private endpoint changes, potentially while you hold a position. Use an official broker API instead.
Alpaca and Interactive Brokers both offer real paper environments, and Alpaca's has a specific structural advantage: paper and live use the same endpoints and the same SDK, so you change only the base URL and the keys. IBKR provides a full paper account alongside the live one with much broader instrument coverage. Robinhood has no paper mode at all.
It depends on the strategy. The free tier is IEX data, which is a single venue carrying a small share of consolidated US volume. That is workable for learning and for slower strategies on liquid names, and misleading for anything sensitive to the true national best bid and offer or to precise intraday prices. Full consolidated data requires a paid subscription, and the difference should be decided before you build a backtest on top of it.
The classic TWS API is not a web API. It requires a local Trader Workstation or IB Gateway process to be running and logged in, you connect over a socket, the connection expects a scheduled daily restart, and there are message pacing limits and historical-data pacing rules that produce confusing failures when tripped. Most developers use a community Python wrapper rather than the raw interface, which helps a great deal but adds a third-party layer.
No. Commission-free retail brokers monetise order flow and spread, which is a cost that never appears as a line item on a statement but does appear in your fills. For a strategy with a small per-trade edge this can matter more than any commission schedule, which is one reason execution-sensitive traders pay for professional-tier routing even though the visible commission goes up.
Decide the number in writing before you start, and make it large enough that the result is not noise. A fixed gate, for example a set number of closed paper trades showing positive realised expectancy, is worth far more than any specific figure, because the point is that the decision was made by someone who was not watching an open position at the time. Paper results still overstate performance, since simulators rarely model queue position, partial fills or your own order's market impact.