Historical ETF Data API: A Developer’s Guide

A useful historical ETF API returns one consistently shaped record per trading day: date, open, high, low, close, and volume. The symbol and supported date range should be explicit, and dates should use a predictable format such as ISO 8601.

Adjusted prices matter when evaluating long periods. Splits and distributions can otherwise make return calculations misleading. Before selecting a provider, verify whether its close series is raw, split-adjusted, or adjusted for both splits and dividends.

A practical history endpoint accepts a symbol, start date, end date, and interval. Keep the first integration simple: request daily observations, validate the first and last returned dates, and check that every OHLC value is positive and internally consistent.

Data Captain stores runtime history by symbol and trading date, making the same series available to charts, indicators, and backtests. This avoids subtle differences between separate quote and simulation datasets.

Once the series is clean, you can calculate total return, CAGR, volatility, maximum drawdown, moving averages, and relative performance. Cache repeated date ranges in your application and record the latest available market date so users understand data freshness.