API Trading Basics: Rate Limits, Throttling and Message Hygiene
Posted: Mon Oct 26, 2026 1:27 pm
Automated order routing through a broker API looks simple until limits appear. Most providers cap how many requests can be sent per second or per minute, and exceeding the cap results in rejected calls, temporary blocks, or disconnections.
Limits often apply separately to different message types. Market data subscriptions, order placement, and account queries usually carry distinct allowances. A script that polls account state in a tight loop can consume quota that order placement needs, creating failures at the worst moment.
Good practice favors event-driven design. Streaming connections push price and order updates, removing the need for constant polling. Requests can be queued behind a small client-side rate limiter, and failed calls retried with growing delays instead of immediate repeats. Idempotent handling matters as well: if a timeout occurs after an order was sent, the system should query order state before resending, otherwise duplicate positions can result.
Logging every request and response with timestamps makes later diagnosis far easier. Documentation from the specific provider is the authority on actual limits, since they differ widely and change over time, and authentication tokens typically expire and need refresh logic.
Limits often apply separately to different message types. Market data subscriptions, order placement, and account queries usually carry distinct allowances. A script that polls account state in a tight loop can consume quota that order placement needs, creating failures at the worst moment.
Good practice favors event-driven design. Streaming connections push price and order updates, removing the need for constant polling. Requests can be queued behind a small client-side rate limiter, and failed calls retried with growing delays instead of immediate repeats. Idempotent handling matters as well: if a timeout occurs after an order was sent, the system should query order state before resending, otherwise duplicate positions can result.
Logging every request and response with timestamps makes later diagnosis far easier. Documentation from the specific provider is the authority on actual limits, since they differ widely and change over time, and authentication tokens typically expire and need refresh logic.