FIX Certification Checklist

FIX certification and onboarding typically fail for the same reasons: session-state edge cases, sequence number recovery, and inconsistent order lifecycle behavior under stress. Use this checklist to validate your FIX integration before you book certification time.

If you want the bigger picture first, follow the FIX testing workflow and then run this checklist before scheduling certification time.

Session Layer Checklist

Logon / Logout: correct credentials, encryption flags, ResetSeqNumFlag behavior (if used)
Heartbeats: HeartBtInt honored; TestRequest handling; disconnect behavior
Sequence numbers: gap detection, resend requests, duplicate handling
Recovery: resend flows do not create side effects (e.g., duplicate executions)
Rejects: proper session rejects for malformed messages and invalid tags
Reset scenarios: sequence reset rules match counterparty expectations

Application Layer Checklist

New Order Single: required tags present; custom tags; symbol/security identifiers
Exec Reports: correct ExecType/OrdStatus transitions; leavesQty/cumQty math
Cancel / Replace: proper OrigClOrdID references; CancelReject handling
Trade capture / allocations: if applicable to your workflow
Error handling: business rejects and order rejects are differentiated correctly

High-Value Failure Scenarios to Test

Most certification failures map directly to the root causes described in why FIX onboarding projects stall.

Disconnect/reconnect during active order flow
Resend request mid-stream while new application messages continue
Out-of-order messages (or delayed acks/executions)
Partial fills followed by cancel / replace
Sequence reset or logon reset expectations not matching

How FIXSIM Helps

A simulator lets you validate these scenarios deterministically, without waiting on a broker or exchange environment. You can replay message flows, trigger rejects, and test recovery logic repeatedly until the behavior is stable.

Run These Test Cases in a FIX Simulator

To run these scenarios in a controlled environment, use a FIX protocol simulator that can emulate counterparties, replay message flows, and validate session behavior before certification.