The Broker Adapter Pattern: One Strategy, Multiple Brokers

How to isolate broker-specific authentication, symbols and order formats behind one internal interface.

Why adapters matter

Broker APIs differ in authentication, symbol names, order parameters, response structures and session behavior. If strategy code calls a broker SDK directly everywhere, changing broker becomes a rewrite.

Define your own small interface

from typing import Protocol

class Broker(Protocol):
    def get_price(self, symbol: str) -> float: ...
    def get_positions(self) -> list[dict]: ...
    def place_order(self, symbol: str, side: str, size: float) -> dict: ...
    def close_position(self, position_id: str) -> dict: ...

Then implement CapitalBroker, OandaBroker, IBKRBroker and so on. Strategy code only sees the protocol.

Normalize symbols

Create a mapping layer. Your internal name might be BTCUSD, while different providers may use an epic, conid, instrument identifier or another symbol format.

Normalize results too

{
  "ok": true,
  "broker": "example",
  "order_id": "123",
  "status": "accepted",
  "raw": {...}
}

Keep the raw response for diagnostics, but let the rest of the application use your normalized fields.