FIXSIM

Name: FIXSIM
Author: gammathreetrading

@gammathreetradingMCP server · External

Test FIX from Claude, ChatGPT, or Cursor: free sandbox FIX sessions or your own FIXSIM instances.

Software testingv0.1.2MITC#

Freeno charge per call

One address for any MCP client. No sign-in needed on this server.

What it does

13 read5 act3 other

Grouped by tool name. At most: moves money, runs code or commands, deletes data, or sends messages for you.

What it costs

Free

Odel charges nothing per call. The publisher may charge for its own service.

Tools

21 · grouped by tool name · checked 12 Oct 2026

Read · 13Look things up

fixsim_list_orders_out
sandbox_get_status
fixsim_list_orders_in
fixsim_list_executions_in
fixsim_list_sessions
fixsim_list_executions_out
fixsim_get_session
fixsim_get_order_in
sandbox_get_orders
sandbox_get_messages
fixsim_list_instances
fixsim_list_securities
sandbox_get_session

Act · 5Change something

fixsim_send_order
sandbox_set_autofill
fixsim_cancel_order_out
sandbox_create_session
fixsim_send_raw_fix

Other · 3Neither hinted nor named

fixsim_act_on_orders
sandbox_act_on_order
sandbox_end_session

Try it in the Inspector

README3 min readView on GitHub

fixsim-mcp

An MCP server for FIXSIM, the hosted FIX protocol simulator. Add it to Claude, Cursor, VS Code, or ChatGPT and test FIX from a conversation:

"Create a FIX 4.4 test session for me, then tell me when my engine has logged on and show me the first order it sent."

Two tool families live on one endpoint:

Tools	Who	Auth
`sandbox_*`	anyone	none. Free, anonymous, 4-hour sessions on the Developer Sandbox
`fixsim_*`	FIXSIM customers	your FIXSIM API key, sent as an `x-api-key` header

Connect

Hosted endpoint: https://mcp.fixsim.com/mcp (read-only variant: https://mcp.fixsim.com/mcp/readonly).

Claude Code

bash

claude mcp add --transport http fixsim https://mcp.fixsim.com/mcp --header "x-api-key: YOUR_FIXSIM_API_KEY"

Leave off --header if you only want the free sandbox tools.

Cursor / VS Code (mcp.json)

json

{
  "mcpServers": {
    "fixsim": {
      "url": "https://mcp.fixsim.com/mcp",
      "headers": { "x-api-key": "YOUR_FIXSIM_API_KEY" }
    }
  }
}

Claude.ai / Claude Desktop: Customize → Connectors → Add custom connector → URL https://mcp.fixsim.com/mcp. Choose authentication None for the sandbox. To use your own instances, add a request header x-api-key (header support in the connector dialog is rolling out; if you do not see it, use Claude Code or Cursor for now).

Tools

Sandbox (no auth)

Tool	What it does
`sandbox_create_session`	Provision a free FIX session. Returns host, port, SenderCompID (your tag 49), TargetCompID (tag 56), BeginString, expiry.
`sandbox_get_status`	Is your engine connected? `connected` / `waiting` / `disabled`.
`sandbox_get_messages`	The FIX message log, raw and parsed. Pass `afterSeq` to poll for new messages.
`sandbox_get_orders`	Working orders your engine sent in.
`sandbox_act_on_order`	Play the exchange: `fill`, `partial`, `reject`, `cancel`.
`sandbox_set_autofill`	Fill every incoming order automatically.
`sandbox_get_session`	Re-fetch the connection card.
`sandbox_end_session`	End the session early.

Sandbox limits: 100 application messages per session per day, 4-hour sessions, a handful of sessions per caller.

FIXSIM instances (API key)

Tool	What it does
`fixsim_list_instances`	Instances your key can access. Start here.
`fixsim_list_sessions`, `fixsim_get_session`	Sessions on an instance: FIX version, CompIDs, role, logged-in state, sequence numbers.
`fixsim_list_orders_in`, `fixsim_get_order_in`	Orders your system sent into FIXSIM, with raw FIX and audit trail.
`fixsim_list_executions_out`	Execution reports FIXSIM sent you (acks, fills, rejects). Filter by ClOrdID.
`fixsim_list_orders_out`, `fixsim_list_executions_in`	The reverse direction, when FIXSIM is the order sender.
`fixsim_list_securities`	Symbols and prices on an instance.
`fixsim_act_on_orders`	Ack, fill, partially fill, reject, cancel, expire… orders your system sent in.
`fixsim_send_order`	Have FIXSIM send you a New Order Single.
`fixsim_cancel_order_out`	Have FIXSIM cancel an order it sent.
`fixsim_send_raw_fix`	Send any raw FIX message on a session.

The /mcp/readonly endpoint exposes the same tools but refuses the ones that send.

Every fixsim_* call is checked against the instances your key is entitled to, and is rate-limited per key (120 calls per minute by default).

Run it yourself

Requires .NET 8.

bash

dotnet run --project src/FixSim.Mcp --urls http://localhost:5199

Configuration (appsettings.json or environment variables such as FixSim__BaseUrl):

Key	Default	Meaning
`FixSim:BaseUrl`	`https://portal.fixsim.com/`	The FIXSIM site whose `/v1` API the `fixsim_*` tools call
`FixSim:PerKeyCallsPerMinute`	`120`	Per-key rate limit at this server
`Sandbox:Enabled`	`true`	Register the `sandbox_*` tools
`Sandbox:BaseUrl`	`https://sandbox.fixsim.com/`	The Developer Sandbox web app
`Sandbox:CallerKey`	empty	Shared secret sent as `X-Sandbox-Caller` so the sandbox can trust server-to-server calls

The server is stateless (Streamable HTTP), so it scales horizontally behind any load balancer.

How it works

The server is a thin client. fixsim_* tools call the public FIXSIM REST API (/v1/...) with your key; sandbox_* tools call the Developer Sandbox's session API. Nothing is stored here beyond a one-minute cache of which instances a key may access. Your API key is forwarded to FIXSIM on each call and never logged.

License

MIT

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