Short answer first, because that's probably why you're here. Yes, most major prop firms let you run an Expert Advisor on a challenge. MT5 was built to run them, and a lot of firms know that plenty of their challenge traders use some form of automation. But "most firms allow EAs" is not the same as "any EA, any way, on any firm". The rules differ, and the rules are the whole game.
So before you load anything onto an account you've paid for, read the firm's rules. Not the marketing page. The actual terms. Here's how to do that, and what a sensible strategy looks like once you have.
Where the rules actually live
Every firm publishes its conditions somewhere. Usually it's the FAQ, the terms of service, or a "prohibited strategies" page. Some bury it. Some spell it out clearly. Either way, that document is the only thing that matters, because if your account gets flagged, that's what they'll point to.
What you're looking for is whether EAs are permitted at all (almost always yes), and then the list of things that aren't. Firms care far more about how you trade than about whether a robot is doing it. A human breaking the rules and a bot breaking the rules get the same outcome.
The tactics that get banned
Most "banned strategy" lists cover the same handful of things. Worth knowing them whether you automate or not.
Latency or arbitrage tricks. Exploiting the gap between the firm's feed and the real market. Firms hate this and screen for it.
Tick scalping and grid or martingale stacking. Some firms ban holding hundreds of micro-trades or doubling position size after a loss. Others allow it within limits. This one genuinely varies, so check.
News straddling. Sitting orders on both sides of a high-impact release to catch the spike. Plenty of firms restrict trading around news entirely.
Copy trading and shared signals. If lots of accounts make the identical trade at the identical second, firms can spot it and may void the lot.
An EA doesn't make any of these safer. If your robot does one of these, it'll do it faster and more consistently, which makes it easier to catch, not harder.
Drawdown is the rule that breaks people
Here's the part that catches more traders than any banned tactic. Every challenge has a maximum loss limit. Usually two of them, a daily loss cap and an overall loss cap. Breach either one, even for a second on an open position, and the account is gone. Done. The profit target gets the attention, but the drawdown rule is what ends most attempts.
This is where automation cuts both ways. A bot will hold its risk discipline at 3am when you're asleep, which is the good news. A bot will also keep trading straight into a bad streak without the flicker of doubt that might make a human stop. If you haven't built the loss limits into the strategy itself, the bot won't invent them for you.
So the strategy you run has to know about the firm's caps. The daily cap and the total cap need to be settings the EA actually respects, not numbers you're hoping it stays under. That's the difference between a robot that fits a challenge and one that's just trading and hoping.
Test it against the limits before you pay
A challenge fee is real money, and the capital behind it is at risk too. Passing is never guaranteed. It depends on the strategy, the market that month, and the trader who set it up and chose when to run it. No tool changes that, and Nebula doesn't make any strategy more likely to pass.
What you can do is stop walking into it blind. Before you spend a penny on a challenge, run your strategy over historical data and watch its worst stretch, not its best. If a backtest shows the strategy at some point sat through a loss bigger than the firm's daily cap, that strategy and that firm don't match. Better to find that out on a chart than on a live account with your fee on the line.
This is the boring, useful work. Look at the deepest drawdown. Look at how the strategy behaves when it's losing, because every strategy loses sometimes. A strategy that's comfortable inside a 5% daily limit is a different animal from one that occasionally needs 9% of room to recover. Same idea, very different fit.
Where Nebula fits
Nebula generates trading strategies, stress-tests them, and exports them as MT5 Expert Advisors you can run wherever you like, including a prop account if the firm permits EAs. It grades each strategy from 0 to 100 on robustness, which is a measure of how much of the result in testing looks like edge rather than luck. That's a testing score, not a forecast, and it's not a claim that any strategy will pass a challenge. What it can do is show you the worst drawdown a strategy hit in testing, so you can decide for yourself whether it fits the caps you're signing up for.
You can download Nebula free, no account and no card, and backtest a single pair to see how this works in practice. Read your chosen firm's rules first. Build for the drawdown limit, not just the profit target. Then decide.
Download Nebula free and test a strategy against the drawdown