FIX Protocol · Acceptor Simulator

A FIX counterparty that does exactly what you tell it to.

Point your FIX engine at a simulated acceptor. Watch every message in real time, and decide precisely how orders fill, reject, or get replaced - without a real venue!

Try the demo

ACME → SIMULATOR · FIX.5.0 SP2 · TLSlive

8=FIXT.1.1 | 9=121 | 35=A | 49=ACME | 56=SIMULATOR | 34=1 | 52=20260519-12:00:01.007 | 98=0 | 108=30 | 1137=9 | 95=44 | 96=9f3c1b4e…a1 | 10=131

8=FIXT.1.1 | 9=89 | 35=A | 49=SIMULATOR | 56=ACME | 34=1 | 52=20260519-12:00:01.061 | 98=0 | 108=30 | 1137=9 | 10=118

8=FIXT.1.1 | 9=157 | 35=D | 49=ACME | 56=SIMULATOR | 34=2 | 52=20260519-12:00:03.114 | 1128=9 | 11=ORD-1042 | 55=AAPL | 54=1 | 60=20260519-12:00:03.114 | 38=100 | 40=2 | 44=187.50 | 59=0 | 10=061

8=FIXT.1.1 | 9=174 | 35=8 | 49=SIMULATOR | 56=ACME | 34=2 | 52=20260519-12:00:03.180 | 1128=9 | 37=EX-7 | 17=E1 | 150=0 | 39=0 | 11=ORD-1042 | 55=AAPL | 54=1 | 38=100 | 14=0 | 6=0 | 151=100 | 10=011

8=FIXT.1.1 | 9=186 | 35=8 | 49=SIMULATOR | 56=ACME | 34=3 | 52=20260519-12:00:03.890 | 1128=9 | 37=EX-7 | 17=E2 | 150=F | 39=1 | 55=AAPL | 54=1 | 38=100 | 32=40 | 31=187.50 | 14=40 | 6=187.50 | 151=60 | 10=097

8=FIXT.1.1 | 9=182 | 35=8 | 49=SIMULATOR | 56=ACME | 34=4 | 52=20260519-12:00:04.402 | 1128=9 | 37=EX-7 | 17=E3 | 150=F | 39=2 | 55=AAPL | 54=1 | 38=100 | 32=60 | 31=187.51 | 14=100 | 6=187.504 | 151=0 | 10=240

8=FIXT.1.1 | 9=121 | 35=A | 49=ACME | 56=SIMULATOR | 34=1 | 52=20260519-12:00:01.007 | 98=0 | 108=30 | 1137=9 | 95=44 | 96=9f3c1b4e…a1 | 10=131

8=FIXT.1.1 | 9=89 | 35=A | 49=SIMULATOR | 56=ACME | 34=1 | 52=20260519-12:00:01.061 | 98=0 | 108=30 | 1137=9 | 10=118

8=FIXT.1.1 | 9=157 | 35=D | 49=ACME | 56=SIMULATOR | 34=2 | 52=20260519-12:00:03.114 | 1128=9 | 11=ORD-1042 | 55=AAPL | 54=1 | 60=20260519-12:00:03.114 | 38=100 | 40=2 | 44=187.50 | 59=0 | 10=061

8=FIXT.1.1 | 9=174 | 35=8 | 49=SIMULATOR | 56=ACME | 34=2 | 52=20260519-12:00:03.180 | 1128=9 | 37=EX-7 | 17=E1 | 150=0 | 39=0 | 11=ORD-1042 | 55=AAPL | 54=1 | 38=100 | 14=0 | 6=0 | 151=100 | 10=011

From zero to a live session

Five steps to a FIX venue that answers to you.

No exchange relationship, no UAT slot, no waiting on a counterparty. Stand up a simulated acceptor, point your engine at it, and drive every fill, reject and replace yourself.

Invite
Get your invite
FixPortal is invite-only. Open your invite link, create your account with Microsoft Entra External ID, and FixPortal provisions an isolated tenant workspace that only you can see.
You've been invited
Create your account to start simulating FIX sessions. You'll sign up with Microsoft - FixPortal never sees your password.
invite ✓8a4f9c2e…
Create your account
New session
Create a session
Spin up a simulated FIX acceptor session: set the version - e.g. FIX.4.4, or FIX.5.0 SP2 over FIXT.1.1 - and its SenderCompID and TargetCompID. FixPortal mints a per-session HMAC shared secret.
Begin String
FIX.4.4
Sender CompID
ACMEBANK
Target CompID
SIMULATOR
Default ApplVerID (optional)

CancelAdd session
03
Connection details
Connect your engine
Point your own FIX engine at the shared host and TCP port. TLS is mandatory - pin the self-signed cert by its SHA-256 fingerprint. Sign every Logon with HMAC-SHA256; paste-ready samples for QuickFIX/n, C#, Python and Java ship in-app.
Connection Details
Endpoint
simulator.fixportal.org:5011TLS required
Server certificate - pin this
SHA-256 9F:3C:1B:4E:…:A1Copy
FIX identity
BeginString
FIX.4.4
SenderCompID
ACMEBANK
TargetCompID
SIMULATOR
Authentication - HMAC-SHA256
••••••••••
RevealCopyRegenerate
Client config & code samples
configC#PythonJava
[DEFAULT] ConnectionType=initiator SSLEnable=Y # …full defaults ship in-app [SESSION] BeginString=FIX.4.4 SocketConnectHost=simulator.fixportal.org SocketConnectPort=5011
Sim config
Shape the responses
Write deterministic when/then rules - evaluated in priority order before any probability draw - then let the random layer handle the rest: accept / error percent, fill count, response and fill timing, a weighted reject pool. Auto-acknowledge, auto-accept cancels and 35=G replaces, per-instrument overrides, custom tags on outbound reports, and a reject-all kill switch. Split an order across brokers and choose whether the fills reach the wire aggregated or separate.
Behaviour
Auto-acknowledge new ordersAuto-accept cancel requestsAuto-accept cancel/replaceReject all inbound orders (kill switch)
Probability
Accept percent (of received orders)
85
%
Error percent (BusinessMessageReject)
5
%
Live blotters
Watch it live
Every inbound and outbound message streams into live blotters in real time over SignalR. Connection details shows each Logon attempt as verified or rejected - with the exact reason.
Incoming messages
Detail MsgType Name Time (UTC) Sender
A Logon 12:00:01 ACMEBANK
D NewOrderSingle 12:00:03 ACMEBANK
F OrderCancelRequest 12:00:05 ACMEBANK
Showing 3 of 3 messages
Connection diagnostics · 1 of 1 verified
12:00:01 - ✓ verified

MsgType	Name	Time (UTC)	Sender
A	Logon	12:00:01	ACMEBANK
D	NewOrderSingle	12:00:03	ACMEBANK
F	OrderCancelRequest	12:00:05	ACMEBANK

deterministic · repeatable · yours

Tweak the config, replay the order, watch the blotter - the venue does exactly what you tell it to, every time.

what an account adds

Your engine connects to a venue you control.

The tools below the fold are free and work on text you paste. This is the part that answers your engine in real time.

Connection details

The acceptor

A private FIX endpoint your own engine logs on to, over TLS. Not a paste box - a socket.

Host: fix.fixportal.org
Port: 9878
BeginString: FIXT.1.1

TLSSHA-256 9f:2c:41:be:07:d3:...

HMACper-session shared secret

configC#PythonJava

Sim config

Rules & behaviour

Deterministic when/then rules, evaluated in priority order before any random draw - then probability and timing underneath.

1whenSymbol = VOD.L

thenReject · OrdRejReason 6

Accept %

Fill count

Auto-AckReject poolReject all

Routes · Pending (2)

Routing

Park an inbound order, split it across brokers, and choose whether the fills hit the wire aggregated or separate.

Pending (2)Recent actions

ORD-2761VOD.LBUYqty 10,0000:42

Wire mode Aggregated

CITIB

60 %

40 %

ApplyApply AutoCancel

Blotter in / out

Live blotters

Every message in and out, streaming as it happens - not a log you audit afterwards.

35=D

NewOrderSingle

35=F

OrderCancelRequest

35=G

OrderCancelReplace

Out

35=8

ExecutionReport · New

35=8

ExecutionReport · Fill

35=9

OrderCancelReject

Logon verifiedHMAC ok

Library

Your library

Custom FIX dictionaries, broker identities and FIXatdl strategies - saved, and assigned per session. The free inspector parses; an account keeps it.

DictionariesBrokersFIXatdl

FIX.4.4Built-in

FIX44_XUser

CITIBBuilt-in

DARK-LPUser

+ Upload

Traffic · Load test

Load testing

Drive the venue at a fixed rate for a fixed duration and watch your engine under load. Rate cap and daily budget apply per account. Enabled on request.

Rate: 5,000 /sec
Duration: 60s

Throughput4,812 /sec

Today126 MB / 500 MB

Enabled on request

where the line sits

Free tools, or a live counterparty.

Free, no sign-in

Decode a message, or a whole engine log
Look up any tag or message
Validate a QuickFIX/N config
Audit a session log afterwards
Inspect a FIXatdl file
Build a message by hand

With an account

Your engine logs on for real, over TLS
A counterparty that answers live
Rules that fire before any random draw
Watch the blotter as it happens
Keep and assign your own strategies
Split an order across brokers

Try the tools How to get access

free, no account needed

FIX tools you can use right now.

Stateless utilities that run on text you paste. No sign-in, no invite, nothing saved.

A FIX counterparty that does exactly what you tell it to.

Five steps to a FIX venue that answers to you.

Get your invite

Create a session

Connect your engine

Shape the responses

Watch it live