mkfix

A FIX protocol testing engine for capital markets connectivity, built on mkio and mkui.

Features

• Session Management -- Configure and run FIX sessions as initiator or acceptor from a live Sessions blotter showing status and sequence numbers, created and edited through modal dialogs. Buttons follow the session's state: Start, Edit, Delete, and Reset Seq only while a session is down, Stop only while it runs; the Reset Seq dialog opens prefilled with the current sequence numbers. Multiple sessions on the same port with different CompIDs. Outgoing timestamp granularity is configurable per session: protocol standard by default (seconds through FIX 4.1, milliseconds from 4.2), or forced to second, millisecond, microsecond, nanosecond, or picosecond.
• Message Viewer -- Live virtualized table of FIX messages in tag=value format, streaming live by default, with time-based paging, per-column filters (value checklists with exclude/include intent, plus numeric and time-range bounds with Today / Last hour / Last 15 min presets on timestamp columns), sorting, and clipboard copy. Heartbeats are hidden by default (every other message type shows); the Messages menu carries one-click views -- Hide Heartbeats, Hide Session Admin, Last 15 Minutes, and Show All, which also restores hidden heartbeats. The same filtering applies across every blotter, and the order and trade blotters open showing today's activity by default.
• Message Detail -- Field-by-field breakdown of the message selected in the Messages viewer, translated through the owning session's dictionary: collapsible header/body/trailer sections and repeating-group trees, drag-resizable columns, and UTC timestamps rendered in a selectable timezone (defaulting to the browser's).
• FIX Dictionaries -- Standard FIX 4.0 through 5.0SP2 dictionaries ship built in; create tweaked copies per test scenario -- either a delta that stays linked to its base version or a standalone document -- edit tag names, enum values, message types, repeating groups, and header/trailer layout in a dedicated editor pane, import/export them as JSON, and bind one per session: both what the session sends and how its messages are displayed follow the bound dictionary.
• Sent Orders & Received Trades Blotters -- Live order state machine driven by ExecutionReports; fill and partial fill records. Send NewOrderSingle from the blotter's New dialog; Replace (Cancel/Replace) and Cancel working orders directly from the blotter -- the Replace dialog opens on the order's full form, prefilled with the terms last entered (the New dialog's or the previous replace's) -- and a fully filled order can still be replaced up to revive it. An accepted cancel or replace moves the order to the request's ClOrdID (per the FIX chain), while an immutable Order ID keeps the order recognizable across the chain; corrections and busts likewise replace the ExecID while an immutable Trade ID groups a fill with its corrections and busts.
• Prefixed IDs -- Every generated ID states its kind: RT ClOrdIDs (routed), OR Order IDs, EX ExecIDs, TR Trade IDs -- followed by a 2-character instance code (the first two letters of the username, so concurrent mkfix users against the same counterparty mint distinguishable IDs) and an 8-digit counter that persists across restarts.
• Received Orders & Sent Trades Blotters -- The other side of the same flow: new orders and incoming cancel and cancel/replace requests all appear on the Received Orders blotter as a pending action, and a single Accept/Reject pair acts on whatever is pending (ExecutionReport New/Canceled/Replaced on accept; ExecutionReport Rejected or OrderCancelReject on reject); orders stay fillable while a request is pending and even after a full fill (overfills are a scenario worth testing), and sent trades can be corrected and busted from the Sent Trades blotter (ExecTransType Correct/Cancel through FIX 4.2, ExecType TradeCorrect/TradeCancel from 4.3 on, always with ExecRefID) -- including trades filled before a replace renamed the order's ClOrdID chain. Every message goes out version-correct: fills report ExecType F from FIX 4.3, tags a version does not define are withheld, FIX 4.0 cancels carry CxlType, and FIXT.1.1 Logons carry DefaultApplVerID.
• Color-Coded Blotters -- Conditional cell and row styling throughout: buy/sell sides, order statuses, exec types, TX/RX direction, and pending requests are colored; heartbeat chatter is dimmed in the Messages viewer. Order and trade action buttons disable while the owning FIX session is down, driven by the session's live status mirrored onto each row.
• Extra Tags on Anything -- Every send action (New, Replace, Cancel, Accept, Reject, Fill, Correct, Bust) takes an optional Extra Tags field in pipe-delimited FIX format (528=A|382=2|375=BRK1|375=BRK2). Custom tags on received orders and cancel/replace requests are captured and prefill the Accept/Reject/Fill dialogs' Extra Tags field, so they can be confirmed or edited and echoed back on the answering ExecutionReport. Pairs are placed by wire position -- header tags in the header, trailer tags before the checksum -- duplicates go out in the order given (that's a repeating group, nested ones included), a tag the message already carries is overridden in place (even 34, 52, or 9/10 for deliberately corrupt messages), and an empty value (21=) deletes the tag for missing-required-field tests.
• Message Replay -- Load production FIX logs and replay them into a test session with speed control, message filtering, and pause/resume.
• IOI & Allocation Viewers -- Indications of Interest and Allocation message tracking.
• Session Protocol -- Logon, Logout, Heartbeat, TestRequest, ResendRequest, SequenceReset, GapFill, PossDupFlag handling, and heartbeat timeout detection.

Installation

pip install mkfix

Or from source:

git clone https://github.com/markuskimius/mkfix.git
cd mkfix
pip install -e .

Usage

mkfix                        # start with defaults (port 8080, mkfix.db)
mkfix -p 9090                # override port
mkfix -d mytest              # use mytest.db
mkfix -d :memory:            # in-memory database
mkfix myconfig.toml          # custom config file

Then open http://localhost:8080 in your browser.

Quick Start

1. Create two sessions with the New button on the Sessions blotter -- one initiator pointing at the other as acceptor on the same port.
2. Start both sessions -- Logon and Heartbeat messages will stream in the Messages pane.
3. Send an order with the New button on the Sent Orders blotter -- see it in the Messages pane and the blotter itself; click any message row to break it out field by field in the Detail pane. On the acceptor side it appears in Received Orders, where it can be accepted, rejected, or filled; fills land in Sent Trades, where they can be corrected or busted.
4. Replay a log from Tools > Replay Control -- load a production FIX log and replay it into a test session.

Configuration

mkfix uses a TOML config file (mkfix.toml). The built-in default is used when no config is specified. Key settings:

port = 8080
host = "0.0.0.0"
db_path = "mkfix.db"

Tables, services, and static routes are also configured in the TOML file. See the built-in mkfix.toml for the full schema.

Dependencies

• mkio >= 0.2.0 -- async microservice framework (aiohttp + aiosqlite)
• mkui >= 0.2.8 -- Web Components UI framework

License

GPL-2.0