To find the native frequency of an economic time series, enter the following URL in your web browser. The output includes the "Frequency" field, which shows the native frequency of that time series.
http://api.stlouisfed.org/fred/series?series_id=DJCA&api_key=your_fred_apikey
The response to the preceding request follows. As the response shows, the native frequency of the Dow Jones Composite Average (DJCA) time series is Daily (frequency=Daily).
<series id="DJCA" realtime_start="2012–11–26" realtime_end="2012–11–26" title="Dow Jones Composite Average" observation_start="1934–01–02" observation_end="2012–11–23" frequency="Daily, Close" frequency_short="D" units="Index" units_short="Index" seasonal_adjustment="Not Seasonally Adjusted" seasonal_adjustment_short="NSA" last_updated="2012–11–26 09:05:12–06" popularity="48">