---
id: simplefix
version: "1.0.17"
license: MIT
license_treatment: permissive
maintenance: active
---

# simplefix — Simple FIX Protocol implementation for Python

License: permissive · Maintenance: active · Downloads: 564.4K/mo

## What it is and what it does

Simplefix is a minimal FIX protocol library that handles the application-layer protocol for financial trading messages. It focuses on message creation, encoding, and parsing without implementing socket handling, recovery, or persistence—those concerns are left to the calling application or a separate FIX engine.

The package provides two main classes: FixMessage for constructing and encoding FIX messages with proper field ordering and checksum calculation, and FixParser for extracting complete messages from byte buffers. It supports standard header tags, UTC timestamp formatting, data fields with length prefixes, and repeating groups. The library is pure Python with no external dependencies and runs on modern Python versions.

Use it for:

- Build FIX messages for transmission to trading venues or counterparties in financial applications
- Parse incoming FIX protocol messages from sockets or message queues in trading systems
- Test FIX protocol implementations by creating and validating message structure and encoding
- Integrate FIX protocol support into Python trading algorithms or market data consumers
- Decode FIX messages for logging, monitoring, or audit trails in financial infrastructure

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

Simplefix provides a lightweight FIX (Financial Information eXchange) protocol implementation for creating, encoding, and decoding FIX messages used in financial trading systems.

Yes. Simplefix is a stable, actively maintained library with no dependencies, permissive licensing, and a clear focus on the narrow problem it solves. Install it if you need to work with FIX messages in Python and want a lightweight alternative to a full FIX engine. Not suitable if you need socket handling, message recovery, or persistence—those require integration with external infrastructure.

## Install

pip install simplefix
uv add simplefix
poetry add simplefix

## Installing simplefix

Before you install: Low friction installation as a pure-Python wheel with no runtime dependencies. Actively maintained with recent commits and stable production status.

License in practice: MIT license permits free use and modification with minimal restrictions, making it suitable for both open-source and commercial projects.

Quickstart:

pip install simplefix

import simplefix

msg = simplefix.FixMessage()
msg.append_pair(8, 'FIX')
msg.append_pair(35, 'D')
encoded = msg.encode()

Verify before relying:

- Whether the package handles all FIX protocol versions or only a subset
- Performance characteristics for high-throughput message processing
- Support for FIX recovery mechanisms or message persistence features

## Package facts

- License: MIT (permissive)
- Python support: unspecified
- Install friction: low
- Maintenance: active
- Downloads: 564.4K/month (top 15,000 on PyPI)
- Known vulnerabilities: none known

## Tags

FIX protocol implementation, financial message encoding, FIX message parser, trading protocol library, FIX message creation, financial data exchange, FIX protocol decoder, financial-trading, protocol-implementation

[View on SkillFed](https://skillfed.io/packages/simplefix) · [View on PyPI](https://pypi.org/project/simplefix/)