About FIX Protocol
What is FIX?
FIX (Financial Information eXchange) is an open electronic communications protocol designed for the real-time exchange of securities transaction information. It is the industry-standard messaging format used by buy-side and sell-side firms, trading platforms, exchanges, and regulators worldwide.
Core Concepts
Messages
FIX communication is message-based. Each message consists of:
- Header — Contains routing and identification information (sender, target, message type, sequence number).
- Body — Contains the business data specific to the message type.
- Trailer — Contains the checksum for message integrity validation.
Tags
Every field in a FIX message is identified by a numeric tag. For example:
| Tag | Name | Description |
|---|---|---|
| 35 | MsgType | Identifies the type of message |
| 49 | SenderCompID | Identifies the sender |
| 56 | TargetCompID | Identifies the recipient |
| 55 | Symbol | Ticker symbol |
| 54 | Side | Buy or Sell |
Session Layer vs Application Layer
FIX separates concerns into two layers:
- Session Layer — Manages connectivity, sequencing, heartbeats, and message recovery. Ensures reliable, ordered delivery.
- Application Layer — Carries business messages such as orders, executions, and market data.
Message Flow
Why FIX?
- Standardized — Eliminates the need for custom integrations between every pair of counterparties.
- Proven — Battle-tested over 30+ years in production at the largest financial institutions.
- Flexible — Supports custom tags for proprietary extensions while maintaining backward compatibility.
- Low Latency — Lightweight text-based protocol optimized for high-speed trading.
- Vendor Neutral — No single vendor controls the protocol; it is maintained by the industry.