A trader’s app and the broker’s trading engine can talk to each other through programming languages called brokerage API. They are RESTful or WebSocket-based services that let you get market data, place orders, manage positions, and ask about the state of your account.
These are the main parts:
- The authentication server makes the access token.
- Endpoints for market data: real-time quotes, depth, and history candles
- endpoints for placing orders → POST/orders with parameters (item type, number, price, order type, and product type)
- Endpoints for changing or canceling orders → PATCH /orders/{order_id}
- Endpoints for positions and holdings → GET /positions, GET /holdings
- Live ticker, order updates, and deal confirmations are all sent over WebSocket streams.
Most of the time, message types are JSON. Rate limits range from 1 to 10 requests per second for placing an order to higher rates for asking market data.
You can use the API to order lifecycle.
When an order is made through API, it goes through several states:
- Sending the request means the broker agrees to it (200 OK answer with order_id).
- You can see an open or pending order at the market.
- Triggered: A stop-loss or cover order is put into action.
- Executed/Filled: A partial or full fill (trade confirmation through WebSocket or asking).
- Rejected—invalid values, not enough margin, circuit limits, and other issues (error codes returned)
- Cancelled / Modified → change started by the user
Tracking of Position and Margin through API
When a position ends, it gives back the present holdings, the average buy price, the realized and unrealized P&L, and the margin used. The ends of the margins show:
- Margin that can be used for stocks, commodities, and currencies
- Margin that was used (blocked for open orders and options)
- Value of collateral (cash and assets pledged)
Automated risk management needs to be able to track margins in real time. When margin falls below certain levels, algorithms must either poll for or subscribe to reports on margin in order to apply stop-loss, trail stop, or scale-out rules.
Management of security and sessions
Brokerage APIs need to be handled safely:
- The API key and secret are never shown to the client.
- Tokens for access are renewed before they expire, usually through the refresh token URL.
- IP whitelisting (not required but usual for heavy users)
- Some dealers offer checksum or signature verification as an extra step when placing an order.
If a session ends in the middle of a trade, changes may not be received; dependable algorithms include logic for auto-reconnect and re-authentication.
Brokerage APIs are the key link between algorithmic or algo trading and real-time market performance. Execution reliability and latency are directly affected by how they are designed, including authentication, order lifecycle, real-time streams, margin tracking, rate limits, and error handling. By understanding these processes, developers can make systems that are strong, can handle errors, and can work in real markets with little to no human input.
