The pages so far have treated an EA as a strategy that opens and closes trades. A large share of the EAs in circulation do something else, and they matter to owners of strategy EAs because they are often run alongside one.
Trade managers
A trade manager attaches to a chart and manages positions that were opened by hand or by another program: setting stops and targets, moving stops to breakeven, trailing them, closing partial positions, or closing everything at a time of day. It is a discipline tool for discretionary traders. Applied to a strategy EA's positions it changes that strategy's exits, and the record no longer belongs to the EA.
Money-management EAs
These calculate position size from a risk percentage and stop distance, and sometimes enforce a maximum open risk. They exist because many strategy EAs do not do this themselves, which is a comment on those EAs. A strategy that sizes by risk already has this built in.
Drawdown controllers
A drawdown controller watches equity and closes every position on the account when a loss threshold is reached, sometimes disabling trading afterwards. It is a blunt instrument that ignores what each strategy intended, and on a multi-strategy EA with its own de-risking logic it can close positions that the EA was managing correctly, at the worst moment, for a reason the EA's own controls would have handled more gently. It has a place on accounts running strategies with no internal risk control, and on prop accounts as a last line before the firm's own limit.
News filters and other utilities
Standalone news filters block trading in a window around releases; some strategy EAs include their own. Trade copiers, alert tools and journaling utilities are also EAs in form.
Running several
Every EA on an account should use a distinct magic number so that it manages only its own trades. Even so, account-level tools such as drawdown controllers act on everything, and two EAs with opposing views on the same instrument can hold both directions at once. The more programs on an account, the harder it is to say which one produced the result.
An owner runs a multi-strategy EA that halves its sizing beyond a 10 per cent drawdown and stops new entries beyond 20. They add a drawdown controller set to close all at 12. In a routine drawdown the controller closes every position at the low, including three that were a day from their targets, and the EA's own ladder never gets to work. The account is down 12 per cent with nothing open, and the controller has to be reset by hand.
A well-built strategy EA contains its own sizing, its own exits and its own drawdown control. Adding utility EAs on top duplicates or fights that logic, and the record then describes the combination rather than the strategy. Run the strategy EA alone unless there is a specific reason, and where a controller is needed for a prop account, set its threshold outside the EA's own limits so that the EA's controls act first.