JSON for Beginners: What It Is and Where It’s Used

In the world of modern technology, data is transmitted and stored in many different formats, but JSON holds a special place among them.

This abbreviation stands for JavaScript Object Notation. Despite the name, the format has long moved beyond just one language and has become a universal way to exchange information between all kinds of programs written in Python, Java, PHP, or any other language. At its core, JSON is simply a text file put together according to strict but simple rules that both computers and humans can understand.

When a developer opens such a file, they can immediately see the structure: where the names are stored, where the values are, where the lists are. It’s this transparency and convenience that have made JSON the de facto standard for web services, mobile applications, and even configuration files.

Introduction

JSON is simply a way to write down information so that it’s easy for both humans and computers to understand.

Imagine you are filling out a form: there are fields (name, age, city) and there are answers. In JSON, these are called “key-value” pairs. The key is the name of the field, and the value is what you put in it. All the information is grouped using curly braces {}, and if you need to list several similar things (like a list of favorite movies), you use square brackets [].

The simplest example of JSON looks like this: { "name": "John", "age": 30, "city": "New York" }. Here, inside the curly braces, are three facts about a person. Each fact is written according to the rule: first the field name in quotes, then a colon, then the value itself.

If there are several values, they are listed separated by commas. This is the foundation of JSON — write your data according to these simple rules, and any programming language will be able to read and use it.

History of Creation and Reasons for Popularity

The JSON format was created by American programmer Douglas Crockford in the early 2000s. Before it, the main method for data exchange was XML — a powerful but verbose language that required a lot of space and was difficult to perceive.

Crockford standardized a simple idea: take the object syntax from JavaScript and make it an independent language for data. XML uses tags that need to be opened and closed, which creates a lot of extra text. JSON, on the other hand, describes data compactly and clearly.

Imagine two programs written in different languages need to agree on a complex transaction. Without a universal translator, it would be too complicated for them. JSON became that translator — simple, fast, and understandable for all sides.

Where JSON is Used

JSON is encountered so often that we use it dozens of times a day without even noticing.

• When you scroll through your social media feed and new posts load without refreshing the page — more often than not, your browser received that data from the server in JSON format.

• Mobile apps for banks, weather, or maps — they are just a pretty shell, while all the data (exchange rates, forecasts, coordinates) comes from servers as JSON structures.

• Many programs store their settings in JSON files — this is convenient because they can be edited manually (filename.json).

• Even databases like MongoDB use a format very similar to JSON for storing information, allowing flexible data structures without rigid schemas.

JSON as a Database

JSON as a database file is both a brilliantly simple and architecturally dangerous solution, with a clear area of application and strict limitations.

At its core, JSON is just text, and any program can read it, parse it, and get a data structure in a fraction of a second.

• For small projects, like a hobby website, a configuration file for a complex program, or a local application without network interaction, a JSON database is an ideal choice.

• You don’t need to set up a separate database server, configure users, or learn SQL — you just read the file and work with it like a native object in your programming language.

• It’s incredibly fast for prototyping and for scenarios where data changes rarely or never at all.

However, as soon as the system grows, and users who read and write data appear simultaneously, problems with data integrity arise.

A JSON file has no built-in mechanisms for transactions, locks, or indexes. If two users try to write data at the same time, you risk getting a corrupted file or losing one of the changes. Searching for a record in a large JSON array requires reading the entire file, which becomes catastrophically slow when the file size reaches several hundred megabytes. Furthermore, the entire structure needs to be kept in RAM for processing, which imposes severe scalability limits.

Therefore, today JSON is used as a database either in conjunction with wrappers like SQLite (which stores data in a binary format but can export to JSON), or in specialized NoSQL solutions like MongoDB, which only superficially resemble JSON but are actually powerful engines with indexing and distributed storage.

For static data, configurations, and caches, JSON is ideal. But for a dynamic web application with dozens of requests per second, it becomes a bottleneck.

JSON Structure: Objects and Arrays

Data in JSON is always organized in one of two ways: either as an object or as an array.

• An object is an unordered collection of key-value pairs, enclosed in curly braces {}. Think of it like a form: each field (name, age, city) has its own value. In JSON, it looks like this: the key is always written in double quotes, followed by a colon, and then the value.

• An array is an ordered list of values, enclosed in square brackets []. The order of elements in an array matters, like in a shopping list. These two structures can be nested within each other infinitely: an array can contain objects, and objects can contain arrays, allowing you to describe data of any complexity.

JSON Syntax: Writing Rules

JSON syntax requires strict adherence to a few simple rules, otherwise the file will not be readable.

• The first and most important rule: all keys (property names) must be enclosed in double quotes. In regular JavaScript, this isn’t always necessary, but in JSON, double quotes are strictly mandatory.

• The second rule: a comma is placed after each key-value pair except the last one. An extra comma at the end of a list is the most common mistake beginners make.

• The third rule: strings must always be in double quotes; single quotes are not allowed. Spaces, tabs, and line breaks do not affect data processing, but they are used for readability — to make the code look neat and understandable for humans.

Data Types in JSON

JSON supports only six data types, and this set is sufficient for the vast majority of tasks.

• Strings are any text in double quotes, for example, “Hello, world!”.

• Numbers can be integers or fractions, written without quotes.

• Boolean values are true or false, also written without quotes and in lowercase.

• null denotes the absence of any value.

• Objects are the collections of key-value pairs in curly braces we’ve already covered, which can contain other objects.

• Arrays are lists of values in square brackets, which can include any type, including other arrays and objects.

This limited set of types ensures compatibility between different programming languages — each language can easily convert these types into its own internal structures.

Advantages of JSON Over Other Formats

Why has JSON replaced XML and become so widespread? There are several reasons.

• First, it’s its simplicity and readability. By looking at a JSON file, even a not-very-experienced developer can quickly understand what data is stored in it.

• Second, it’s compactness. JSON is much less verbose than XML, which reduces the volume of transmitted data and speeds up application performance.

• Third, it’s language independence. Parsers for JSON exist for all popular programming languages, making it a universal bridge between systems.

• And finally, processing speed. Thanks to the format’s simplicity, programs can parse JSON very quickly, which is critical for high-load web services.

If you’re familiar with the web programming language PHP, here are two examples.

JSON example (user data):

{
"name": "John Smith",
"email": "john@example.com",
"age": 30,
"isActive": true,
"hobbies": ["soccer", "reading"]
}

The same array in PHP (just an array, not JSON):

$user = [
"name" => "John Smith",
"email" => "john@example.com",
"age" => 30,
"isActive" => true,
"hobbies" => ["soccer", "reading"]
];

In PHP, this is called an associative array (keys are strings). The syntax: square brackets [] create an array, the arrow => links a key to its value. Elements are separated by commas. This array is identical in structure to the JSON we saw.

JSON in Web Development and APIs

The most common role of JSON today is as the language of communication between the client and the server in web applications and APIs.

When a developer needs their service to get data from another service, they exchange JSON messages.

For example, a payment service sends a request to process a payment in the form of a JSON object with the order ID, amount, and payment method. The server processes this object and returns a response — also in JSON. This approach allows breaking down large applications into many small, independent services (microservices) that can be easily replaced and updated individually, as long as they “understand” each other through a single data format.

How to Work with JSON in JavaScript

Although JSON is based on JavaScript syntax, it’s simply a string that needs to be converted into a usable object.

In JavaScript, there is a built-in JSON object with two main methods. JSON.parse() takes a string containing JSON data and turns it into a real JavaScript object that you can work with: access properties with dot notation, loop through arrays, and so on.

The reverse process — JSON.stringify() — takes a JavaScript object and turns it into a string in JSON format, ready to be sent to a server or saved to a file. This is the absolute foundation when creating modern web applications where data constantly circulates between the browser and the server.

How to Write JSON Correctly

To avoid mistakes, you need to follow a few simple recommendations.

• Always check your finished JSON with online validators like JSONLint (or others). These services will highlight the error and tell you where a comma or quote is missing.

• When writing JSON manually, try to keep the structure as flat and clear as possible — don’t get carried away with excessive nesting, as complex hierarchies are harder to maintain.

• Use meaningful names for keys, so that even a month later, it’s clear what a particular field means. If the JSON is generated programmatically, trust this job to your language’s built-in libraries — they will correctly place quotes and commas.

Common Beginner Mistakes

The most common mistake when writing JSON manually is an extra comma after the last element of an array or object. In JSON, commas are placed only between elements, not after the last one. Parsers are strict, and upon finding an extra comma, they will simply refuse to read the file.

The second frequent issue is using single quotes for strings or keys. JSON only allows double quotes. When a beginner writes {'name': 'John'}, it’s an error because the correct way is {"name": "John"}. People also often forget to put quotes around keys, but in JSON, keys must always be strings in quotes.

Another surprise for beginners is that you cannot write comments in JSON. Unlike configuration files in other languages where you can leave an explanation after a hash or double slash, JSON does not support comments at all. If you try to add an explanation to the file, the parser will see it as part of the data and throw an error.

Another technical complexity is escaping special characters. If you need to use double quotes inside a string, they must be escaped with a backslash: “He said: “Hello””. The same goes for the backslash itself — it needs to be doubled: “C:\\Program Files”.

JSON-LD as a Special Use Case

In the world of SEO and web development, a variation of JSON called JSON-LD (Linked Data) is widely used.

It is the same JSON, but designed to transmit structured data to search engines. The JSON-LD code is placed inside a <script> tag on the page and describes for Google and Yandex exactly what is on that page: an article, a product, an event, or frequently asked questions.

Thanks to this markup, search engines can display rich snippets with ratings, prices, and images.

The syntax of JSON-LD follows the same rules as regular JSON, but adds the required @context and @type fields, which point to the Schema.org vocabulary and the type of object being described.

• Check out our related review here: Schema Markup: What It Is, History, and SEO Role Explained

JSON Validation and Debugging

When your JSON is ready, especially if it’s important data for your website’s functionality, it needs to be validated.

There are special tools for this purpose.

Google offers the Rich Results Test, which will show whether the search engine correctly understands your markup and if there are any errors in it. Universal validators, such as the Schema Markup Validator, are suitable for any type of structured data.
If you’re working with JSON in code, use debuggers and the browser console — they will highlight the problematic spot.

The main rule: if a program won’t read your JSON, look for an extra comma, a missing quote, or an unescaped character. Often the problem is solved with a couple of minutes of careful inspection.

Example Breakdown

Let’s break down a simple block as an example.

This example demonstrates all the main JSON data types: strings, numbers, boolean values, objects, and arrays, as well as nesting. It fully complies with JSON syntax (double quotes for keys and strings, no comments, correct delimiters):

{
"title": "War and Peace",
"author": "Leo Tolstoy",
"publicationYear": 1869,
"genres": ["novel", "historical fiction"],
"available": true,
"price": 59.99,
"publisher": {
"name": "Alphabet Books",
"country": "Russia"
},
"reviews": [
{
"user": "reader123",
"rating": 5,
"comment": "A masterpiece!"
},
{
"user": "bookworm",
"rating": 4,
"comment": "Very long, but worth it"
}
]
}

Let’s break down this simple JSON block and explain what each element is responsible for:

• { – The opening curly brace denotes the start of an object. An object contains a set of key-value pairs.

• "title": "War and Peace", – The key title with a string value. Strings must be in double quotes. The comma at the end means another property will follow.

• "author": "Leo Tolstoy", – Another string, the key author.

• "publicationYear": 1869, – The key publicationYear with a number value (integer). Numbers are written without quotes.

• "genres": ["novel", "historical fiction"], – The key genres with an array value (square brackets). The array contains two strings. Arrays can contain any data type, including objects.

• "available": true, – The boolean value true. In JSON, true, false, and null are valid. They are all written in lowercase without quotes.

• "price": 59.99, – A floating-point number (decimal).

• "publisher": { ... }, – The key publisher, whose value is a nested object (in curly braces). Inside the publisher object are its own keys: name and country. This nesting allows for structuring data.

• "reviews": [ ... ] – The key reviews, whose value is an array of objects. Each object in the array represents one review with the fields user, rating, and comment. Array elements are separated by commas, with no comma after the last element.

• } – The closing curly brace completes the entire object.

This next example shows JSON with a root array:

[
{
"id": 1,
"name": "Everest",
"height": 8848
},
{
"id": 2,
"name": "K2",
"height": 8611,
"firstAscent": 1954
},
null,
[
"additional information",
{"key": "value"}
],
true,
42,
"just a string",
[]
]

Again, let’s break down the elements, focusing only on those not covered earlier to avoid repetition:

• [ in the first line – The opening square bracket means the root element of the entire document is an array. Arrays can contain any valid JSON values, listed separated by commas.

• null – A special value denoting the absence of data. It appears as a standalone array element.

• [ "additional information", {"key": "value"} ] – An array within an array (nesting). This element itself is an array containing a string and an object. Nesting can be of any depth.

• true – A boolean value. It can be simply true in an array without a key.

• 42 – A number as a standalone array element.

• "just a string" – A string as an array element.

• [] – An empty array. A valid element meaning an empty list.

• { "id": 2, "name": "K2", "height": 8611, "firstAscent": 1954 } – Notice that inside the object for the second element, an additional field firstAscent appears, which the first one doesn’t have. JSON allows different object structures within the same array — this is the format’s flexibility.

All array elements are separated by commas, with no comma after the last element. Object keys are still in double quotes.

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