// the find
connamara/quickfixn
QuickFIX/n implements the FIX protocol on .NET.
QuickFIX/n is a .NET port of the QuickFIX FIX protocol engine, covering FIX 4.0 through 5.0 SP2. It's the go-to option if you need to connect a .NET system to a broker or exchange that speaks FIX — there's essentially no competition in this space on .NET. Maintained by Connamara, a firm that actually uses it in production.
The acceptance test suite is genuinely impressive — hundreds of scenario files covering every edge case in the FIX session protocol spec, including garbled messages, sequence number gaps, and simultaneous resend requests. The code generation approach for message and field classes from DataDictionary XML files is the right call; hand-maintaining 500+ message types across six protocol versions would be a maintenance disaster. It targets .NET 8 now (as of 1.13), so you're not stuck on Framework. Active maintenance with a recent push in July 2026 means it's not abandonware.
590 forks vs 521 stars is a tell — most people fork it to patch their own broker quirks rather than contributing back, which means there are N private forks with N different fixes that will never be upstreamed. The API surface shows its C++ QuickFIX heritage: session configuration is flat INI-style files, and the callback-based IApplication interface feels like 2005. No async support — everything is synchronous under the hood, which is a real problem if you're building anything that needs to handle high message volume without spinning up dedicated threads per session. Documentation on the website is thin for anything beyond basic session setup.