Check field from JSON response


I’m trying to check a specific field from JSON response, unsuccessfully.
Could you, please, provide any advise?

My intention is to check whether the field ‘id’ is contained in the JSON response, “id”: “12123-24H-MADRID”.


import http from 'k6/http';
import { check, sleep } from 'k6';

export default function () {
    const url = 'http://localhost:8080/offer-evaluate';
    let headers = { 'Content-Type': 'application/json' };
    let data = {
        "offerExternalId": "ashgGGHgGH02",
        "offerId": "12123",
        "rateModelId": 1,
        "version": 1,
        "rateModelDesc": {
          "key": "TARIFF_STANDARD"
    let res =, JSON.stringify(data), { headers: headers });
     check(res, {
      "status is 201": r => r.status === 201,
      "id": r => r.json()["id"] === "12123-24H-MADRID"


        "id": "12123-24H-MADRID",
        "tariffModelId": "12123",
        "productId": "24H",
        "origin": {
            "name": "MADRID",
            "regexpr": null,
            "code": "ES-M",
            "scales": null

Your response appears to be an array of JSON objects (judging by the presence of square brackets), so to access the id property of the first object in the array, you would need to do something like res.json()[0]["id"] or res.json()[0].id.


You nailed it!. It works just fine, thanks a lot mate. I really appreciate your help.

Can you please help me how to access a value in