Konstas Markets Desk: An FX Dealing Room on One Mac

Articles · October 2026 · Ioannis (John) Konstas

A complete foreign-exchange dealing room that runs on one Mac mini: live two-way prices from eight banks, Reuters-style dealing conversations, client calls, orders, forwards and money markets, a full back office with double-entry accounting, and every formula of the ACI Dealing Certificate.

Interbank FX is learnt on the desk, not in a textbook. The Markets Desk recreates that desk: a market that never stops moving, counterparties who answer in dealer shorthand and refuse stale prices, clients who call with fifteen seconds to quote, and a back office that confirms, settles and books every deal. It was built as a study companion for the ACI Dealing Certificate (exam 002-101) and grew into a full trading simulator with a web dealing room and an old-school terminal.

Everything runs locally. The server listens only on the Mac's loopback address, so nothing on the network or the internet can reach it. The only things it fetches are public reference prices.

Capabilities

• Live interbank market — EUR/USD, GBP/USD, USD/JPY, USD/CHF, AUD/USD, USD/CAD, EUR/GBP and gold, anchored to ECB reference rates and the live gold price, moving continuously.
• Eight competing banks — Each quotes its own two-way price and size, shades prices with its inventory, goes off-line, and refuses stale prices with “last look”.
• Reuters-style dealing — Open a conversation with a bank code, ask “EUR 10”, deal with MINE or YOURS, close with BIBI. Confirmations come back with value date and settlement instructions.
• Clients who call you — Corporates, funds and a central bank ask for two-way prices. Quote within fifteen seconds; tougher clients need tighter prices.
• Orders — AT BEST, limit and stop orders, GTC and GFD validity, one-cancels-other take-profit and stop-loss, immediate-or-cancel.
• Forwards, swaps, money markets — Forward curves from overnight to one year, outright forwards, B/S and S/B FX swaps, deposits and loans with interest accrual.
• Back office — Trade tickets, confirmation matching with random breaks, settlement through nostro accounts, end of day at 17:00 New York.
• Double-entry ledger — Every settlement, revaluation, carry and interest posting is a journal; the trial balance balances in every currency.
• Risk and performance — Positions, average rates, realised and open P&L in USD, position and stop-loss limits, win rate, drawdown, client hit rate.
• Study tools — 46 ACI formula calculators verified against the official sample answers, an exam-practice quiz on live numbers, and more than 100 HELP topics.
• Two front ends — A web dealing room with click-to-deal prices and an amber terminal with candlestick charts and Tab completion, on the same live market.
• Always on — Starts at login, opens both screens, saves its book continuously and backs itself up, encrypted, every night.

The screens

Screenshots are from a demonstration copy of the simulator. All prices, banks, clients and amounts are simulated; the banks are fictional.

Life of a deal

1. Price. Eight banks quote two-way prices around the market mid. In a conversation you ask for a price: EUR 10 → 1.1203/05.
2. Deal. MINE buys at 1.1205. The bank confirms: TO CONFIRM AT 1.1205 I SELL 10 MIO EUR VAL 13OCT26 · MY USD TO ATLB NY.
3. Position. The position, average rate and open P&L update at once; limits are checked.
4. Ticket. The back office captures a ticket: trade date, value date, both currency amounts.
5. Confirmation. The counterparty's confirmation arrives seconds later and is matched. About one in twenty disagrees and becomes an exception.
6. End of day. At 17:00 New York, positions are revalued at closing rates, P&L and carry are posted, and the business date rolls forward.
7. Settlement. On the value date the two currencies move through the nostro accounts and the ticket is marked settled.

Command reference

Commands are typed at the DEAL> prompt and are not case-sensitive. Amounts are in millions of the first currency (gold in thousands of ounces). Tab completes words, and HELP followed by any word explains it with an example.

Dealing conversations

Electronic broker and orders

Forwards, swaps and money markets

Book, back office and study

How the market works

Price process

Each currency pair follows a random walk scaled to its typical annual volatility (EUR/USD 7%, USD/JPY 10%, gold 15%) over a 252-day trading year. EUR/GBP is derived from EUR/USD and GBP/USD so the crosses never disagree. Prices are pulled back towards their real reference levels with a half-life of about six simulated hours, more firmly beyond ±3%, so the simulation stays close to the real market over time.

Reference data

Currencies anchor to the European Central Bank's daily reference rates; gold anchors to the live spot price. Both refresh every four hours. Money-market rate levels and forward points are computed from simulated interest rates, labelled as such on every screen.

Banks and liquidity

Eight fictional banks quote around the mid with their own spread and size. A bank that is long shades its prices lower, quotes update at different moments, and a quote the market has moved through is refreshed so the best bid never crosses the best offer. Dealing on a stale price, or for more than the size shown, can be refused with last look.

Events

News shocks (central banks, data releases, intervention, risk-off, the occasional flash crash) jump prices and widen spreads, with a one-hour cooldown per currency. Other banks trade with each other on the tape, and clients call at random with sizes that fit their type.

Reproducibility

Randomness comes from a seeded xoshiro128** generator, the same family as C++'s standard generators, so a session can be replayed from its seed.

Limits

50 million per pair (gold 20,000 oz), 150 million net open position, and a USD 250,000 daily stop-loss, with warnings when breached.

Back office & accounting

Spot FX is off-balance-sheet between trade date and value date. On the value date each deal settles: the currency bought arrives in its nostro, the currency sold leaves it, and each leg is booked against a currency position account so every journal balances in its own currency. End of day revalues open positions at closing mids and posts the unrealised result in USD, reversed the next day; realised results, tom/next carry and interest are posted alongside.

Ticket statuses run captured → matched → settled. A break shows as unmatched; if it is still unmatched on the value date the ticket fails and settles late once resolved. Dates follow market conventions: spot is T+2 (USD/CAD T+1), month tenors use modified-following with the end/end rule, and money markets use ACT/360 or ACT/365 by currency.

Architecture

              Mac mini — listens on 127.0.0.1 only
  ┌────────────────────────────────────────────────────┐
  │  server.mjs ── HTTP, event stream, JSON API         │
  │      │                                              │
  │  sim/engine.mjs ── market, banks, orders, risk      │
  │      ├── sim/backoffice.mjs  tickets · settlement · ledger
  │      ├── sim/rates.mjs       tenors · points · money markets
  │      ├── sim/quiz.mjs        exam questions          │
  │      └── data/sim-state.json the live book           │
  └───────────▲───────────────▲───────────────▲────────┘
              │               │               │
      Terminal client   Web dealing room   Formula desk
       (cli/desk.mjs)      (/dealing)     (46 calculators)
  every 4 h ──► ECB reference rates · live gold price

The server is plain Node.js with no third-party packages. The engine ticks four times a second, saves the book every five seconds and on every deal, and pushes a snapshot to every connected screen over a server-sent event stream. Both front ends are thin: they render the snapshot and send commands back as JSON.

API reference

All routes live under /api/sim on 127.0.0.1:9300. Requests that change anything must be JSON and carry the header X-Desk: 1; a web page from another site cannot send that header, which protects the local server from cross-site requests.

Operations

• Always on — the server starts automatically at login and opens both screens once the market is up.
• Persistence — the whole book (positions, deals, orders, back office, ledger, price history) is saved continuously and survives restarts.
• Backups — code and the live book are backed up every night, encrypted, off the machine.
• Testing — every change is tested on a separate copy of the simulator, never against the live book.
• Security — loopback-only listener, host-header check, a custom header required for every change, a strict Content-Security-Policy, and no third-party server packages.

Formula desk

Forty-six calculators cover the ACI FMA formula sheet effective 22 June 2026 for the Dealing Certificate (002-101), Operations Certificate (002-201) and Diploma (003-102): spot amounts and cross rates, forward points and outrights, short dates, interpolation, deposits and rollovers, discount instruments and CDs, repo with margin or haircut, forward-forwards, FRAs and single-period swaps, futures, bonds, swaps, options strategies, volatility, VaR and the Basel III ratios. Each shows the formula, an explanation, the working, and can be saved to a blotter. A test script checks the results against every numeric answer in the official sample questions.

Konstas Markets Desk is a training system. Prices are simulated around public reference rates, the banks and clients are fictional, and no real money is involved. ACI and ACI FMA are trademarks of their owners; the formula sheet is referenced for study purposes.

Research and direction by Ioannis (John) Konstas; compiled and finalized with AI assistance.