Using rrdtool & datadog

gistfile1.md

rrdtool fetch localhost_load_1min_5.rrd AVERAGE --start -15min

             load_1min           load_5min          load_15min

1334860500: 6.0133333333e-02 1.3013333333e-01 1.2003333333e-01
1334860800: 1.0983333333e-01 1.0010000000e-01 9.0100000000e-02
1334861100: 7.0133333333e-02 1.0000000000e-01 9.0000000000e-02
1334861400: -nan -nan -nan

Extract time stamp & first column

> rrdtool fetch localhost_load_1min_5.rrd AVERAGE --start -15min | gawk '/^[0-9]+:/ && !/nan/ {print substr($1,1,  length($1)-1), $2}'
1334860500 6.0133333333e-02
1334860800 1.0983333333e-01
1334861100 7.0133333333e-02

The curl it following the JSON format in here or use one of our client libraries.