1
Client order ID
A stable identifier generated before submission and reused for reconciliation.
Lesson · Algorithmic and Automated Trading
Broker APIs and Order Lifecycle
Submit, query, cancel, and reconcile orders through a broker adapter while treating every response and status update as asynchronous state.
Core concepts
What to understand
Keep the boundaries, state, and authority explicit.
2
Order lifecycle
Created, submitted, accepted, partially filled, filled, canceled, expired, or rejected.
3
Unknown state
A timeout means the result is unknown until the broker is queried or an update arrives.
Interactive lab
Broker Order Lifecycle Lab
Submit an order, step through acknowledgments and fills, inject timeouts, and reconcile the final broker state.
Broker Order Lifecycle Lab
Deterministic synthetic educational data · no broker or live-market connection
SYSTEM MODEL
Process
Treat broker communication as asynchronous
State changes can arrive later, partially, or more than once.
Identify
Create a client order ID and persist the intent.
Submit
Send once, then record the broker ID and response.
Reconcile
Consume updates and query the broker when local and external state disagree.
Knowledge check
Check your understanding
Select one answer for each question. Feedback appears immediately, and a wrong choice is answered on its own terms before the rule is restated.
1. A request timeout proves that the broker:
The broker may have accepted the request before the response was lost.
2. Why use a client order ID?
A stable ID supports idempotency and reconciliation.
3. A partial fill should update:
Partial execution changes portfolio state immediately.
4. A 100-share buy limit at $108.53 is working; the stream reports 55 shares filled. What changes?
55 × $108.53 = $5,968.92 of cash consumed; 100 − 55 = 45 remaining; position 55 shares. All three change at once, and the risk engine reads all three.
Practical rules
- Persist order intent before network submission.
- Treat timeouts as unknown state.
- Consume streaming updates and periodically reconcile by query.
Common mistakes
- Marking an order filled after an HTTP success response.
- Generating a new ID for every retry.
- Ignoring partial fills and cancel races.
References
Official reading
These sources cover algorithmic controls, market access, broker APIs, system operations, or security.
Alpaca · Working with Orders
Official example of submitting orders and receiving asynchronous order-status updates.
SEC · Rule 15c3-5 Market Access Controls
Official rule overview describing pre-trade financial and regulatory risk controls for broker-dealers with market access.