FIXSIM Developer Sandbox: a Free Hosted FIX Test Endpoint

A live FIX counterparty, free, in one click. Create a sandbox session, point your FIX engine at it, and watch your logons, orders, and fills parse into readable FIX in your browser. No account. No install. No counterparty paperwork.

Prefer to ask an AI assistant? The sandbox is also available as an MCP server, so Claude, Cursor, or ChatGPT can create the session and read the wire for you: see Test FIX from Claude, ChatGPT, or Cursor.

Open the Sandbox

How It Works

Create a session. Pick a FIX version and click once. You get a host, port, and assigned CompIDs.
Connect your engine. QuickFIX, your own stack, anything. The sandbox answers your logon immediately.
Trade against yourself. Send an order and it lands in a working-order blotter on the page. Click Fill, Partial, Reject, or Cancel and watch the execution report stream back to your engine in real time.

FIXSIM sandbox after a full order lifecycle: the working-order blotter shows one order filled and one partially filled, and the live feed lists the logons, NewOrderSingles, and ExecutionReports in both directions. — A sandbox session after one order each way. The blotter on the left is where you act as the counterparty; the feed on the right shows every message parsed, in both directions, as it hits the wire.

FIXSIM sandbox connection card showing the host, port, assigned SenderCompID and TargetCompID, BeginString, and session expiry, with a green Connected indicator.

This is everything your engine needs: host, port, assigned CompIDs, and the FIX version you picked. The indicator turns green the moment your logon is accepted. Nothing to configure on our side.

What You Get, Free

A hosted FIX acceptor with a real internet network path (test the connectivity a localhost setup cannot)
FIX 4.0, 4.2, 4.4, and 5.0 SP2 over FIXT 1.1
A live message viewer: every message parsed into readable fields, with the raw FIX underneath
A mini blotter where you act as the counterparty: fill, partial fill, reject, or cancel incoming orders
Automatic acks, optional auto-fills, session recovery by URL

Sandbox limits: one session at a time, 100 application messages per day, 4-hour sessions, assigned CompIDs, nothing persists. That is the point: it is a sandbox. Need persistence, your own CompIDs, the Rule Builder, replay, or the REST API? Those live in the full product, from $500 per month with a 7-day free trial.

Common Questions

Is there a free version of FIXSIM?

Yes. The FIXSIM Developer Sandbox is a free, hosted FIX test endpoint: create a session in one click, connect any FIX engine, and act as the counterparty yourself. No account required. For real testing work, paid plans start at $500 per month.

Do I need an account to use the FIXSIM sandbox?

No. There is no signup, no email, and no login. Click Create sandbox session, point your FIX engine at the assigned host, port, and CompIDs, and start sending messages.

Which FIX versions does the free sandbox support?

FIX 4.0, 4.2, 4.4, and 5.0 SP2 over FIXT 1.1. The sandbox runs the same engine as the commercial FIXSIM platform.

What are the sandbox limits?

One session at a time, 100 application messages per day, and sessions expire after 4 hours. Heartbeats and session traffic are free. Nothing persists: for persistent sessions, your own CompIDs, and automated scenarios, FIXSIM plans start at $500 per month with a 7-day free trial.

How is the sandbox different from a self-hosted FIX simulator?

It is already running. There is nothing to install, build, or configure: the sandbox is a real network endpoint with actual TLS-capable internet connectivity, so you can test the network path a localhost simulator cannot.