How to Use JSON Server: Build a Fake REST API in Seconds

What is JSON Server?

A Node.js package that creates a full REST API from a simple JSON file. It works with a single-file database (db.json) and auto-generates every CRUD endpoint your frontend needs — no backend code to write. It's ideal for prototyping, demos and teaching.

Why Use JSON Server?

When a project starts and the backend isn't ready, the frontend team is blocked. JSON Server removes that delay and lets you build the UI as if there were a real API.

• Instant REST API setup — seconds
• No database needed — just a JSON file
• Speeds up frontend development
• Great for demos and training environments
• Works without any backend dependencies

Installation

Install globally or per-project. The most common modern approach is via an npm script.

# Global
npm install -g json-server

# Verify install
npx json-server --version

Create a Database File

JSON Server expects a JSON object at the root level. Each key becomes a collection that's automatically available at /key.

{
  "posts": [
    { "id": 1, "title": "Hello", "views": 120 },
    { "id": 2, "title": "Mock API", "views": 87 }
  ],
  "comments": [
    { "id": 1, "postId": 1, "body": "Awesome!" }
  ],
  "profile": { "name": "DevCards" }
}

Start the Server

The command below watches db.json and starts an API on port 3001. Use --port to choose another port and --delay to simulate latency.

npx json-server --watch db.json --port 3001 --delay 250

REST API Endpoints

All verbs are auto-generated; GET, POST, PUT, PATCH, DELETE write directly to the file.

GET    /posts       → all posts
GET    /posts/1     → one post
POST   /posts       → create (id assigned)
PUT    /posts/1     → replace whole record
PATCH  /posts/1     → partial update
DELETE /posts/1     → delete

Query Features

Rich query parameters cover filtering, search, sort and pagination so you get an experience close to a real API.

# Filtering
GET /posts?views_gte=100

# Full-text search
GET /posts?q=hello

# Sort
GET /posts?_sort=views&_order=desc

# Paginate
GET /posts?_page=1&_limit=10

Relationships

Foreign-key fields support embed and expand. Nested routes like /posts/1/comments work out of the box.

# Comments of a post
GET /posts/1/comments

# Embed: include comments inside the post
GET /posts?_embed=comments

# Expand: include the parent post
GET /comments?_expand=post

Key Features

JSON Server alone gives you a remarkably capable mock backend:

• Full CRUD support
• Auto-generated routes
• Custom routes via middleware
• Watch mode auto-reloads on file change
• Realistic latency simulation with --delay
• CORS enabled

Use Cases

Where JSON Server shines:

• Starting the frontend before the backend
• Prototyping APIs quickly
• Building demos with middleware and seed data
• Teaching and training
• Pairing with libraries like React Query

Summary

JSON Server turns a db.json file into a working REST API instantly. It shortens development time, is great for prototypes and works seamlessly with libraries like React Query. It's not built for production — use it for demos, prototypes and development.