Usar Google Spreadsheets como API

api.php

<?php

$id = '1ERm4xxxTNLeZOStU5vG4KdVIZMDp3rT_xxxfJsdck';

$url = 'https://spreadsheets.google.com/feeds/list/' . $id . '/od6/public/values?alt=json-in-script';

$json = file_get_contents($url);
$json = str_replace( array('gdata.io.handleScriptLoaded(',');'), '', $json);
$json = json_decode($json);

$items = array();

foreach( $json->feed->entry as $cols ){
    $cols = (array)$cols;
    $props = array();
    foreach( $cols as $key => $col ){
        if( strstr($key, 'gsx$') ){
            $key = str_replace('gsx$', '', $key);
            $val = $col->{'$t'};
            $props[$key] = $val;
        }
    }
    $items[] = $props;
}

echo json_encode( array('data' => $items) );