Free article spinner/paraphraser also available on runkit as a free api.

spinner.js

const synonyms = require("synonyms");

const WordPOS = require('wordpos'),
      wordpos = new WordPOS();
      
var cors = require('cors');
var express = require("@runkit/runkit/express-endpoint/1.0.0");
var app = express(exports);
app.use(cors());

app.get('/', async function(request, response, next) {
	let text = request.query.text;
	let rate = parseFloat(request.query.rate);
    
    let result = await rewrite(text, rate);
    
    response.send(result);
});

async function rewrite(text, rate) {
  text = text.split(" ");
  for (var i = 0; i < text.length; i++) {
    let word = text[i].replace(/[^a-zA-Z ]/g, "");
    
    let others = synonyms(word, await POS(word)) || [word];
    
    let new_word = others[~~(Math.random()*others.length)] || word;
    if (Math.random() > rate) {
      new_word = word;
    }
    text[i] = text[i].replace(word,new_word);
  }
  return text.join(" ");
}

async function isNoun(word) {
  let promise = new Promise((resolve, reject) => {
    wordpos.isNoun(word,(r)=>{resolve(r)});
  });
  let result = await promise;

  return result;
}
async function isVerb(word) {
  let promise = new Promise((resolve, reject) => {
    wordpos.isVerb(word,(r)=>{resolve(r)});
  });
  let result = await promise;

  return result;
}
async function isAdjective(word) {
  let promise = new Promise((resolve, reject) => {
    wordpos.isAdjective(word,(r)=>{resolve(r)});
  });
  let result = await promise;

  return result;
}
async function isAdverb(word) {
  let promise = new Promise((resolve, reject) => {
    wordpos.isAdverb(word,(r)=>{resolve(r)});
  });
  let result = await promise;

  return result;
}

async function POS(word) {
  if (await isAdverb(word)) {
    return "r";
  } else
  if (await isAdjective(word)) {
    return "s";
  } else
  if (await isNoun(word)) {
    return "n";
  } else
  if (await isVerb(word)) {
    return "v";
  }
}