Algorithmic Trading Guide: From Idea to Running System

What algorithmic trading actually means

Algorithmic trading means expressing trading rules as code that generates and manages orders. That covers an enormous range: a script that emails you signals at the close, a system that places bracket orders automatically, and a colocated market-making engine are all algorithmic in the same sense and share almost nothing operationally.

The minimum architecture

  MARKET DATA          Ingest, validate, store, detect staleness
        |
        v
  SIGNAL ENGINE        Compute indicators, evaluate rules
        |
        v
  PORTFOLIO STATE      Current positions, open orders, equity
        |
        v
  RISK LAYER           Position sizing, exposure limits,
                       VETO authority over every order
        |
        v
  EXECUTION            Order placement, amendment, cancellation,
                       fill handling, retry logic
        |
        v
  LOGGING              Every decision, every order, every fill
        |
        v
  MONITORING           Heartbeat, alerts, reconciliation,
                       KILL SWITCH

The risk layer sits between signal and execution deliberately.
No order reaches the broker without passing it, including
orders the strategy considers urgent.

The ordering matters. A common failure is embedding risk checks inside the strategy, where a bug in the strategy can bypass them. An independent risk layer that validates every order against absolute limits catches strategy bugs before they reach the market.

The risk layer in detail

• Maximum position size per instrument, in both units and notional, checked before every order.
• Maximum total exposure, gross and net, across the portfolio.
• Maximum order size relative to recent average volume, to prevent a fat-finger or a bug from sending an enormous order.
• Price sanity checks: reject any order more than a defined percentage away from the last price.
• Order rate limits: a maximum number of orders per minute, which catches runaway loops.
• Daily loss limit that halts all new orders and optionally flattens positions.
• Duplicate order detection, since retry logic is a common source of accidental double positions.
• Stale data check: refuse to trade on data older than a defined threshold.

Execution and order management

1. 1

   Track order state explicitly

   Pending, submitted, partially filled, filled, cancelled, rejected. Most execution bugs come from assuming an order is in a state it is not.

2. 2

   Handle partial fills

   Your position may be half of what the strategy expects. Every subsequent calculation must use actual filled quantity rather than intended quantity.

3. 3

   Reconcile with the broker continuously

   Compare your recorded positions against the broker’s record on a schedule. A desynchronised position is an unmonitored directional bet.

4. 4

   Make retries idempotent

   Use client order IDs so that a retry after a timeout cannot create a second order. This is the single most important execution safeguard.

5. 5

   Handle rejections explicitly

   Insufficient margin, invalid price, market closed, instrument halted. Each needs a defined response, not a generic retry.

6. 6

   Place protective orders immediately

   The stop should be submitted as soon as the entry fills, not on the next cycle. A position without a stop during a system failure is the worst case.

Monitoring and failure handling

A realistic path to a running system

1. Trade the strategy manually for a month. You cannot automate rules you have not yet fully specified, and manual trading exposes the ambiguities.
2. Automate the scan and the signal. Generate alerts; place orders by hand. Verify signal counts match the backtest.
3. Automate order placement with confirmation. The system prepares orders; you approve each one. This catches sizing and routing bugs cheaply.
4. Automate fully, supervised, at minimum size. Watch every cycle for weeks. Budget for finding bugs, because you will.
5. Add the risk layer and monitoring before scaling. Not afterwards. These are prerequisites for size, not refinements.
6. Scale gradually on demonstrated reliability, measured in clean sessions and reconciliation matches rather than in profits.