Algorithmic Execution for Funds, Prop Desks and Brokers: Use Your Broker's Algorithms, Buy an EMS, or Build Your Own

Algorithmic execution means giving one large order to software that feeds it into the market in smaller pieces, so that the trade moves the price less. Funds, proprietary trading desks and brokerages can use the algorithms their broker offers, buy an execution management system (EMS) or build their own execution layer. Which one fits depends on how many brokers you use, since an EMS reaches many of them from one screen, and on whether you can measure the result. In the EU, an investment firm that trades algorithmically and buys or outsources its algorithms stays responsible for them.

What do execution algorithms do?

A large order sent in one piece shows the whole market what you want, and it can push the price against you. An execution algorithm splits that order, called the parent order, into smaller child orders and decides when to send each one. The common styles differ in the price they try to stay close to:

• VWAP, the volume-weighted average price. The order follows the market's trading volume, so more of it trades when more of the market trades. Interactive Brokers describes its VWAP algo as “Designed to achieve or outperform the VWAP price, calculated from the time you submit the order”. This style suits a large trade you are willing to spread across the day.
• TWAP, the time-weighted average price. Here the order goes out in slices at an even pace over a set period, whatever the volume is doing. Trading Technologies describes its TT TWAP as “breaking up an order into smaller slices and submitting those to the market incrementally and systematically”.
• Implementation shortfall. The aim is to stay close to the price at the moment you decided to trade. Waiting carries the risk that the price moves away, so the algorithm weighs that risk against the cost of trading faster. Interactive Brokers offers a close relative called Arrival Price. It targets “the bid/ask midpoint price at the time the order is submitted”, which can be later than your decision, with a “user-assigned level of market risk which defines the pace of the execution”. Choose it when a move in the price while you wait would hurt more than the cost of trading quickly.

How is an EMS different from an OMS?

An order management system (OMS) keeps the official record of what each order asked for and what happened to it. An EMS is the trader's tool for working that order in the market, usually by sending it to a broker's algorithm or straight to a venue.

Vendors use these names loosely, so go by what the product page lists. FlexTrade calls FlexTRADER a “broker-neutral, truly multi-asset, execution management system”. Trading Technologies' page for its TT OMS lists “Broker-native algos, synthetic orders and rules-based routing across size, account, product and venue”. That is execution work, even though the product is called an OMS.

Should we just use our broker's algorithms?

There is very little for you to run here. You send the parent order over your existing connection and pick a style, and the broker maintains the algorithm and the links to venues.

You usually cannot see inside a broker's algorithm, and you see the child orders only as far as the broker reports them. Ask whether the broker's own venues or desks can take the other side of those orders, and how that is disclosed to you.

Comparing brokers is also hard, because each broker grades its own work in its report and two brokers may build their reports differently. For a fair comparison you need your own records or a neutral tool.

Is an EMS worth buying?

An EMS puts many brokers' algorithms behind one screen, and it collects the fills. FlexTrade says traders can “Connect with over 300 global brokers” through its network, and its FX section offers “100+ Broker algos”. Virtu describes its Triton EMS as “a global, broker-neutral, multi asset-class platform”. These are the vendors' own claims, so test them against the brokers you use.

You pay a vendor for this, and a feature you need arrives when the vendor decides to build it. The brokers' algorithms inside stay closed. Some vendors add algorithms of their own: FlexTrade describes “our array of malleable, globally-capable trading algorithms” for its EMS, so ask who can see and change that logic. The EMS also sits in the path of your orders, so ask what happens to working orders when it fails.

When should we build our own execution layer?

Building makes sense when execution is part of your edge and the products you tested cannot do what you need. You will usually see at least one of these signs:

• Your strategy needs execution logic tied to its own signals, and handing that logic to a broker would reveal it
• You trade enough that a small, measured saving on each order pays for a team
• You need several instruments or venues treated as one position, and the tools you tested handle them one at a time
• Your transaction cost analysis shows a cost you can name, and broker algorithms have not removed it

Before you commit to a full build, look at the halfway option. Trading Technologies says its ADL tool lets you “design, test and deploy custom algos without writing a single line of code”. Your logic then runs on another company's platform, which shortens the work and ties you to that platform.

Do not build yet if you do not know what execution costs you. You could not tell whether the new layer did better than the algorithm it replaced.

Someone also has to run it. An execution layer needs connections to each venue or broker, market data, pre-trade risk checks and people who answer alerts during trading hours. For an EU investment firm that trades algorithmically, it also brings the testing and review duties described below. Without those people, and with no plan to hire them, stay with a broker or an EMS.

What do we own on each route, and how hard is it to switch?

• Your broker keeps its own copy of the child orders, so ask for them in a form you can store. With an EMS, get in writing that you can export every order and fill.
• A broker or EMS vendor owns its execution code. If you build, you can own the code, as long as the contract says so and lists anything the builder keeps.
• Switching to a new broker or EMS means new connections and new testing. A briefing from the European Securities and Markets Authority (ESMA), the EU's securities regulator, lists “Replacing third-party providers or data feeds” among the changes where retesting is good practice.

How do we measure execution quality?

Transaction cost analysis (TCA) compares the prices you got with a reference price. The answer depends on which reference you use, so choose it before you look at the results.

A strict reference is the price at your decision or when the order reached the desk, and those two can differ. A 2015 FlexTrade article uses the desk: “Implementation shortfall is a measure of the difference between the average execution price and the price when the order arrives on the trading desk.” VWAP is a weaker test for a large order, because the order forms part of the volume it is measured against. To make the numbers mean something:

• Record your own timestamps for the decision, the order's arrival at the desk, its arrival at the broker and each fill
• Count what did not trade, because an order that half filled can look cheap while the rest of the position moved away from you
• Compare like with like by instrument and order size, and split orders between brokers on a set plan, so each gets comparable ones
• Use one calculation for every broker, and wait for enough orders in each group before drawing a conclusion

Vendors sell tools for this. FlexTrade lists “FlexTCA for real-time and historical performance measurement”, and a FlexAlgoWheel tool that automates routine orders using “historical and real-time TCA data”. Any of these tools still depends on the timestamps you record yourself.

When you execute for clients, regulators expect this kind of checking. Article 27 of MiFID II, the EU's main law for investment firms, tells firms to “take all sufficient steps to obtain, when executing orders, the best possible result”. It also tells them “to monitor the effectiveness of their order execution arrangements and execution policy”.

In the US, FINRA is the self-regulatory body for broker-dealers. FINRA Rule 5310 covers members that route customer orders automatically or internalise them and do not review each order. Those members must make “regular and rigorous reviews of the quality of the executions of its customers' orders”. The rule adds that “At a minimum, a member must conduct such reviews on a quarterly basis”.

What do EU rules require for algorithmic trading?

Algorithmic trading in the EU falls under Article 17 of MiFID II, which ESMA carries in its online rulebook. An investment firm doing this “shall have in place effective systems and risk controls”, and must make sure “its systems are fully tested and properly monitored”. It must also “notify this to the competent authorities of its home Member State and of the trading venue”.

Article 1(5) extends Article 17(1) to (6) to “members or participants of regulated markets and MTFs” that need no authorisation. Funds and their managers are otherwise exempt from MiFID II under Article 2(1)(i), so a fund should first check whether these duties reach it at all. If a client outside MiFID II reaches a venue through a broker's direct electronic access, ESMA says “the DEA provider bears sole responsibility for the compliance of its client”.

The definition in Article 4(1)(39) is wide, covering trading where “a computer algorithm automatically determines individual parameters of orders”. It leaves out “any system that is only used for the purpose of routing orders to one or more trading venues”, so a tool that only routes an order and sets none of its trading parameters falls outside the definition. ESMA's non-binding Supervisory Briefing on Algorithmic Trading in the EU (ESMA74-1505669079-10311, 26 February 2026) lists “Slicing orders prior to execution” among the activities that qualify when automated. It says investment firms authorised to deal on own account “are most likely engaging in algorithmic trading”. A trader's sign-off on each order does not take a firm out of scope when an algorithm has set the parameters, ESMA adds.

The detail sits in Commission Delegated Regulation (EU) 2017/589, known as RTS 6. ESMA says it “recognises the need for proportionality in applying the testing provisions”, so the depth of testing varies with the firm. These parts matter most when you choose a route:

• Testing. Before any “deployment or substantial update”, Article 5 requires “clearly delineated methodologies to develop and test such systems, algorithms or strategies”. Article 6 adds conformance testing, a check that your system works correctly with each venue's system, including “when connecting to that trading venue through a sponsored access arrangement for the first time”, and against “the system of the direct market access provider” when you reach the venue through one.
• Kill functionality. Under Article 12, a firm “shall be able to cancel immediately, as an emergency measure, any or all of its unexecuted orders”. That must work at “any or all trading venues to which the investment firm is connected”. It must also be able to say which algorithm sent each order and who is responsible for it.
• Annual self-assessment. Article 9 says a firm “shall annually perform a self-assessment and validation process” and issue a validation report, which its risk management function draws up and senior management approves. ESMA expects this “on an article-by-article basis”.
• Stress testing. ESMA's briefing, citing Article 10, says firms should be able to show that systems “can process twice the volume of the highest volume of trading reached by the investment firm during the previous 6 months”.
• Limits on the whole order. ESMA says limits placed only on child orders do not meet its expectations, and that firms should “apply volume and/or value limits to both the parent order and the child orders”.

This article quotes RTS 6 as adopted, from legislation.gov.uk. All regulator and vendor pages were opened on 9 November 2026. Countries outside the EU and US have their own rules.

Who is responsible when the algorithm belongs to someone else?

Buying software leaves the duty with you. Article 4 of RTS 6 says an investment firm “shall remain fully responsible for its obligations under this Regulation” where it “outsources or procures software or hardware used in algorithmic trading activities”. ESMA's briefing says that with third-party algorithms or execution tools, the firm “remains fully and solely responsible for compliance with MiFID II and RTS 6”.

Orders sent to a broker's algorithm may be a different case. ESMA does not name that setup. Its nearest example is an order started by an algorithm that another market participant runs, such as where one firm generates orders and another executes them: “the entity executing the orders is deemed to be engaging in algorithmic trading for the purposes of MiFID II and thus bears responsibility for ensuring RTS 6 compliance”. Where both firms engage in algorithmic trading, “both firms will remain subject to the obligations of RTS 6”. If only one of the two is an investment firm, ESMA says “that entity shall be deemed responsible for RTS 6 compliance”. Which side of that line your setup falls on is a question for your lawyer.

For an outsourced algorithm or tool, including an EMS that a provider runs for you, check the contract against ESMA's expectation. It wants arrangements that give the firm “the unconditional capacity to monitor, suspend, or terminate algorithmic trading where necessary, without dependence on the third-party provider’s consent or intervention”. If only the vendor's support desk can stop your orders, that test is hard to meet.

What do US rules require for algorithmic trading?

SEC Rule 15c3-5 applies to a broker-dealer with market access, and to one that gives a customer or anyone else access. Such a firm must “establish, document, and maintain a system of risk management controls”, including ones that “Prevent the entry of erroneous orders, by rejecting orders that exceed appropriate price or size parameters”. Those controls “shall be under the direct and exclusive control of the broker or dealer”, although it may hand specific regulatory controls to a customer that is itself a registered broker or dealer, by written contract and after due diligence, and it stays responsible. Each year, the firm's chief executive or equivalent officer must certify them.

A fund that trades through a broker-dealer and is not one itself falls outside those words, though its orders still pass through that broker's controls. A broker-dealer with market access that runs its own execution layer carries this duty itself. The rule covers access to “trading in securities on an exchange or alternative trading system”, so check separately for futures and other products.

FINRA published Regulatory Notice 15-09 in March 2015. The notice gives member firms guidance on “effective supervision and control practices” for algorithmic strategies, across risk assessment, code development, testing, trading systems and compliance. Among its effective practices are a quality assurance process in which “testing is performed independently of code development”, and “mechanisms by which the firm may quickly disable the algorithm”.

What does each route cost?

This article quotes no prices, and the FlexTrade, Virtu and Trading Technologies product pages read for it showed none. Ask a broker whether its algorithms are included in your commission, and ask an EMS vendor who pays when a new broker or venue is added. Building your own adds people to run it for as long as it runs and, for firms in scope, the compliance work described above.

What should we ask an EMS vendor or a firm that would build our execution layer?

• Which of our brokers' algorithm suites are live on your system today, and who updates them when a broker changes a parameter?
• What do we see about each child order, with which timestamps, and can we export all of it?
• Can our staff cancel every unexecuted order across every venue at once, without calling you?
• Who sets the limits on parent and child orders, and how do we prove they were active on a given day?
• How does the system behave when a venue or data feed stops in the middle of an order, and what happens to that order after a restart?
• Where do we run tests, and how do we arrange conformance testing with each venue or broker?
• Which records do you give us for the annual self-assessment?
• Can you show this working on a system that runs today?

Where does amBrain fit?

amBrain publishes this blog. It describes one part of its trading work in one line: “amBrain builds algorithmic trading infrastructure: order execution, market data and pre-trade risk controls.” That line does not name an execution management system.

amBrain has been building software since 2019. On how it works with clients, it says: “Three formats: full delivery, a dedicated team, or engineers embedded in your team.” Its line on ownership is “The client keeps full ownership of the product and the code, except our reusable components.” Ask for the list of those components by name before you sign.

This article is not a case study and describes no client work. Nothing in it says that amBrain has built, licensed or integrated an execution management system or an execution algorithm for any client. The quotations come from the published pages of ESMA, FINRA, FlexTrade, Trading Technologies, Virtu and Interactive Brokers, from the text of RTS 6 on legislation.gov.uk and from the text of SEC Rule 15c3-5 on govinfo.gov. The article claims no relationship between amBrain and any of them, recommends none of their products and gives no amBrain prices or timelines.

It is not legal or investment advice either. Check the rules that apply to your firm with a lawyer in each market where you trade. If amBrain is on your shortlist, ask it the same questions as any other firm.