How to Read JSON File: Clear, Practical Examples for Every Developer

JSON is the backpack of modern data—lightweight, flexible, and easy to carry between systems. If you’ve ever worked with APIs, configs, logs, or test fixtures, you’ve met it. In this guide, we’ll demystify how to read JSON file content across popular languages, highlight common pitfalls, and share simple patterns you can reuse anywhere.

What JSON Is and why it matters

JavaScript Object Notation (JSON) is a text format for structured data. It’s human-readable, maps neatly to objects and arrays, and is supported by virtually every language. Because it’s just text, you can store it on disk, send it over HTTP, and version it in Git without special tooling. The trick is reading it correctly: open the file, decode it using the right character set (usually UTF-8), and parse it into native structures (objects, maps, lists).

How to Read JSON File in Python

Python’s built-in json module makes this almost effortless.

import json
from pathlib import Path

path = Path("data.json")

# Option 1: Read and parse in one go
with path.open(encoding="utf-8") as f:
    data = json.load(f)       # dict/list
print(data["name"])

# Option 2: If you already have a string
raw = path.read_text(encoding="utf-8")
data2 = json.loads(raw)

A few tips: always set encoding="utf-8" to avoid surprises on non-ASCII characters; prefer json.load() for files and json.loads() for strings. For very large files, consider streaming libraries such as ijson to avoid loading everything into memory.

How to Read JSON File in JavaScript (Node.js and the browser)

In Node.js, read a file as text, then JSON.parse it:

import { readFile } from "node:fs/promises";

const raw = await readFile("data.json", "utf8");
const data = JSON.parse(raw);
console.log(data.name);

In older Node versions you might see require('./data.json'), but explicit reading plus JSON.parse is clearer, safer, and works consistently with ESM.

In the browser, you typically fetch JSON instead of reading from a local filesystem:

const res = await fetch("/data.json");
if (!res.ok) throw new Error(`HTTP ${res.status}`);
const data = await res.json();
console.log(data.name);

Note how Response#json() does both the text read and parse for you. If you’re handling very large payloads or streaming APIs, use the Streams API for chunk-wise processing.

How to Read JSON File in Java and C#

Both languages offer first-class parsers that map JSON to objects.

Java (Jackson example):

import com.fasterxml.jackson.databind.ObjectMapper;
import java.nio.file.*;

var mapper = new ObjectMapper();
var json = Files.readString(Path.of("data.json"));
var user = mapper.readValue(json, User.class); // or Map<String,Object>
System.out.println(user.getName());

C# (.NET 6+, System.Text.Json):

using System.Text.Json;
var raw = await File.ReadAllTextAsync("data.json");
var user = JsonSerializer.Deserialize<User>(raw); // or JsonDocument for DOM
Console.WriteLine(user.Name);

Prefer strongly-typed models for compile-time safety. If the shape is dynamic, use a DOM (JsonNode/JsonDocument in C#, Map/List in Java) and access properties defensively.

Common Pitfalls When Reading JSON Files

• Wrong encoding: JSON defaults to UTF-8. Mismatched encodings cause mojibake or parse errors.
  
• Trailing commas: JSON doesn’t allow them; { "a": 1, } will fail.
  
• Comments: Plain JSON doesn’t support comments. Use JSONC only if your parser explicitly supports it.
  
• Huge files: Loading multi-GB files into memory can crash your app. Stream or chunk instead.
  
• Type mismatches: Don’t assume keys exist or have the type you expect—validate before using.
  
• Locale traps: Numbers and dates are JSON primitives/strings, not localized formats. Parse them explicitly.

At-a-Glance: Methods and Libraries

This table doubles as your quick reference. Pick the row for your platform, follow the pattern, and you’re done.

Performance, Encoding, and Large Files

When you expect large JSON files, favor streaming. In Node, read with streams and parse incrementally using a SAX-style parser. In Python, tools like ijson let you iterate over arrays without loading them entirely. In Java, Jackson’s JsonParser streams tokens; in C#, Utf8JsonReader is the low-level, allocation-friendly option. These approaches preserve memory and speed up processing on constrained environments like containers.

Encoding deserves equal attention. Save and read as UTF-8 consistently. If a partner sends ISO-8859-1 or Windows-1251 files, recode them to UTF-8 before parsing. Finally, validate structure with a schema (e.g., JSON Schema) when you control the contract. That single step catches missing fields and type errors early, well before production traffic hits.

Quick Checklist and Next Steps

If you came here wondering “how to read JSON file,” the essentials are straightforward: open the file as UTF-8 text, parse to native structures, and validate the expected shape. For production systems, add streaming for big data, explicit error handling, and schema checks. When your data source is remote and you need reliable connectivity patterns (like stable egress or geo-routed requests for third-party APIs), services such as proxys.io can help you keep integrations steady at scale.

With these patterns and snippets, you can read JSON confidently in Python, JavaScript, Java, or C#, and you’ll know exactly what to tweak as files grow larger or contracts evolve.