The FIX Protocol: How Institutions Send Orders

FIX Protocol

FIX is the standard messaging protocol for institutional trading. Learn how FIX sessions, messages and tags work, a sample order message and when traders use FIX.

Intermediate3 min readUpdated 3 Oct 2026

Lesson 12 of 27

The Financial Information eXchange protocol, known as FIX, is the standard language that banks, brokers, funds and exchanges use to send orders and execution reports to each other. It began in 1992 as a project between Fidelity Investments and Salomon Brothers to replace phone calls for equity trading, and it is now maintained by the nonprofit FIX Trading Community. FIX is used across equities, futures, foreign exchange and fixed income worldwide. Most retail traders never touch it directly, but it sits behind much of the order flow they interact with.

Why FIX exists#

Before FIX, each broker and client connection needed its own custom format. FIX gave the industry a common vocabulary: a "new order" or "execution report" means the same thing whichever firms are talking. That makes it far easier for a fund to connect to many brokers, or a broker to many venues.

How a FIX message looks#

A FIX message is a series of tag and value pairs. Each tag is a number with a defined meaning, and pairs are separated by a special SOH character, shown here as a vertical bar.

8=FIX.4.4|9=148|35=D|49=CLIENT1|56=BROKER1|34=215|52=20261003-14:30:01.123|
11=ORD-20261003-0007|55=AAPL|54=1|38=100|40=2|44=185.50|59=0|60=20261003-14:30:01.120|10=072|

Tag	Name	Value here
8	BeginString	FIX version 4.4
35	MsgType	D = New Order Single
49 / 56	Sender / Target	Who is talking to whom
34	MsgSeqNum	Message sequence number 215
11	ClOrdID	Client's own order ID
55	Symbol	AAPL
54	Side	1 = Buy
38	OrderQty	100
40	OrdType	2 = Limit
44	Price	185.50
59	TimeInForce	0 = Day
10	CheckSum	Integrity check

The body length and checksum values above are illustrative. FIX engines calculate them automatically.

Key message types#

MsgType	Message	Direction
A	Logon	Both
0	Heartbeat	Both
D	New Order Single	Client to broker
F	Order Cancel Request	Client to broker
G	Order Cancel/Replace Request	Client to broker
8	Execution Report	Broker to client: acknowledgements, fills, rejects
3	Reject	Either side, for malformed messages

Sessions and sequence numbers#

A FIX session starts with a logon and keeps running with heartbeats. Every message carries a sequence number. If a side sees a gap, it sends a resend request and the missing messages are replayed. This makes FIX reliable: an order or fill cannot silently disappear. See Sequence Numbers, Dropped Packets and Out-of-Order Messages.

Who uses FIX#

Asset managers and hedge funds sending orders to brokers.
Brokers routing to exchanges and other venues. See Order Routing and Smart Order Routing.
Exchanges, many of which offer FIX order entry alongside faster native binary protocols. See Binary Protocols.
Active traders with direct market access, through brokers that offer FIX connections. See Direct Market Access and Sponsored Access.

FIX versus other options#

	FIX	REST and WebSocket APIs	Native binary protocols
Users	Institutions	Retail and crypto	Latency sensitive firms
Format	Text tag and value	JSON	Compact binary
Speed	Fast	Moderate	Fastest
Standardisation	Very high	Venue specific	Venue specific

Getting started with FIX#

Open source engines such as QuickFIX (with versions for C++, Java and Python) handle sessions, sequence numbers and parsing. Brokers that offer FIX usually provide a test environment and a specification document listing the tags they support. See Working With Exchange and Broker APIs.

Frequently asked questions#

What is the FIX protocol?#

A standard messaging protocol that financial firms use to send orders, cancellations and execution reports electronically.

Who created FIX?#

It started in 1992 as a project between Fidelity Investments and Salomon Brothers and is now maintained by the FIX Trading Community.

Do retail traders use FIX?#

Rarely. Most use broker REST or WebSocket APIs, though some brokers offer FIX to active traders.

Next, learn what level 2 data shows in Market Data Levels: Level 1, 2 and 3.

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Next lessonMarket Data Levels: Level 1, 2 and 3Level 2 data shows bids and offers at multiple prices beyond the best quote. Learn level 1, 2 and 3 data, how to read depth, its limits and how traders use it.