Parse JSON Responses
Extract fields using ArduinoJson.
Parse JSON Responses is a free Arduino & IoT Academy lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Arduino & IoT Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Responses Are Just Text
A server reply arrives as one long string. To use a value inside it, you first have to pull that value out cleanly.
Why Not Search by Hand
Hunting through text with indexOf is fragile. A real JSON parser understands the structure and gives you fields safely.
Meet ArduinoJson
The ArduinoJson library turns a JSON string into objects you can read by key. Install it from the Library Manager.
#include <ArduinoJson.h>Make a Document
Create a JsonDocument to hold the parsed data. It is the container ArduinoJson fills in for you.
JsonDocument doc;Parse the String
Call deserializeJson() with your document and the response text. This reads the string and fills the document.
deserializeJson(doc, body);Check for Errors
deserializeJson returns an error you should test. Bad or partial JSON should be caught before you trust any field.
if (deserializeJson(doc, body)) {
return; // parse failed
}Read a Field by Key
Access a value with its key, just like a dictionary. Tell ArduinoJson the type you expect for that field.
float temp = doc["temp"];Read Nested Values
For nested JSON, chain the keys. Each bracket steps one level deeper into the structure to reach the value you want.
int id = doc["device"]["id"];Loop Through an Array
If a field is a JSON array, you can walk it with a for loop and read each element in turn.
for (JsonVariant v : doc["list"].as<JsonArray>()) {
}Size the Document Right
A JsonDocument uses memory. Keep it just big enough for your data, since RAM on a microcontroller is limited.
Strings Need Care
Treat a parsed string as valid only while the source text still exists. Copy it out if you need it to last longer.
Quick Check
Which function actually converts the JSON text into a readable document?
Recap
You used ArduinoJson to deserialize a response, checked for errors, and read fields and arrays by key. Raw text is now real data. 🎉
Frequently asked questions
Is the “Parse JSON Responses” lesson free?
Yes — the full text of “Parse JSON Responses” is free to read here on the web, and the Arduino & IoT Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Arduino & IoT Academy course, upgrade to CoddyKit PRO.
What will I learn in “Parse JSON Responses”?
Extract fields using ArduinoJson. You practise Arduino & IoT Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Arduino & IoT Academy?
No prior experience is required. Arduino & IoT Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Parse JSON Responses” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Arduino & IoT Academy lesson?
Yes. Every Arduino & IoT Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- GET Data from an API
- POST Sensor Readings
- Parse JSON Responses
- Use HTTPS Securely