When you send a POST request containing your article in a ‘text’ variable, you get the following response:

{
“status”: “ok”,
“text_words”: “18”,
“unique_keywords”: “15”,
“density”: [
{
“text”: 3,
“is”: 2,
“this”: 1,
“a”: 1,
“sample”: 1,
“and”: 1,
“i”: 1,

Here you have a full list of relevant words taken from your article, with specific keyword density.