If you’re looking for a fast way to mock APIs from HAR files, MockCraft is a lightweight Node.js tool designed just for that.

The Problem: When Mocking Becomes a Bottleneck

During frontend or integration development, having a reliable mock server is crucial. Whether you’re building features before the backend is ready, debugging complex UI flows, or just trying to simulate production-like behavior in a local environment — mocking saves time and headaches.

Like many developers, I initially turned to popular tools like Postman and Mockoon. They’re well-known and offer mock server capabilities, so I figured I was covered. But I quickly ran into frustrating limitations.
• 🧪 I was using a mock API service with a free trial license.
• 📉 That came with a monthly request limit, which I unexpectedly hit during testing.
• 💸 Even with a paid license, I realized I’d still need to create example responses manually for each endpoint.
• 🧱 The workflow was slow, repetitive, and error-prone. Export HAR files from Chrome… create Postman mocks… paste in responses… again and again.

At some point, I found myself thinking:

“I just wanted to test my frontend with real captured traffic, not spend hours manually writing mock routes.”

I knew there had to be a better way — or if there wasn’t, I’d make one.

The Solution: How to Mock APIs from HAR Files

To eliminate the manual overhead, I built a custom Node.js tool that takes a .har file — the kind you can export straight from your browser’s DevTools — and turns it into a fully functional mock server. No extra setup. No hand-written routes.

🛠️ What it does:
• ✅ Reads the HAR file captured during real API traffic
• 🔍 Parses request method, path, and response body
• 🧠 Identifies dynamic segments (like UUIDs) and replaces them with route parameters (e.g., /answer-sheets/:id/start)
• 📦 Outputs a mockRoutes.js file that maps each API call to its mock response
• 🚀 Boots up an Express server and serves responses instantly
• ⚡ Requires zero manual work once you have the HAR

This means: as soon as your browser has seen the API, your mock server can simulate it — with real request/response data.

No need to:
• Copy/paste response payloads
• Write custom mock logic
• Configure routes manually

It just works.

Why No Other Tool Could Solve This

Before building my own solution, I explored all the popular tools — hoping one would just work. But every option fell short in at least one critical way.

What I needed was a tool that could:
• Understand real captured traffic
• Handle dynamic paths like /answer-sheets/:id/start
• Work with real examples, not templates
• Launch a mock server instantly

None of the existing tools gave me that experience. So I built one that did.

What Makes My Tool Special

Why Mock APIs from HAR Files Instead of Manual Setup

Most mock tools feel like overkill — or underpowered. I wanted something lean, developer-first, and automation-ready. Here’s what sets my tool apart:

🔄 HAR → mocks in seconds

Just export a .har file from your browser, and the tool instantly converts it into mockable routes — including the responses.

📦 Fully local and lightweight

It’s a simple Node.js script. No cloud, no bloat. Everything runs on your machine with minimal dependencies.

⚡️ No internet or GUI required

Run everything from the terminal. Perfect for CI pipelines, offline development, or environments where GUI-based tools aren’t practical.

🔥 Handles dynamic paths

The tool automatically replaces UUIDs and other dynamic parts of the URL with route parameters like :id, so one route can serve many requests.

🚀 Ready for future extensions

WebSocket support, dynamic query matching, and delay simulation — all are on the roadmap. It’s built with flexibility in mind.

It’s not just a mock server — it’s a developer productivity hack.

Bonus: How I Might Extend It

This started as a quick utility to make my frontend life easier — but it’s evolving fast. Here are some powerful extensions I’m planning:

🔁 WebSocket Support

Mocking APIs is one thing, but simulating real-time events is another. I want to emit custom WebSocket messages when specific routes are triggered — like sending a testStarted event right after /start is called.

🧠 Load Local Storage Context

Many frontends rely on tokens or state stored in localStorage. I plan to auto-load predefined values so the app “just works” without manual prep.

🖥 UI for Inspecting Active Mocks

A lightweight dashboard where I can view, edit, or toggle mock routes live — perfect for debugging and demos.

🔄 Convert to OpenAPI

Imagine turning real traffic into usable OpenAPI specs for documentation or schema validation. That’s on my radar too.

This project isn’t just a stopgap — it’s becoming a full mock ecosystem, tailored for real-world frontend workflows.

Conclusion: Build What You Need

Sometimes, no existing tool fits just right — especially when you’re juggling real-world development constraints, deadlines, and repetitive tasks. That’s when you stop waiting and build what you need.

My HAR-to-Mock Server tool was born out of frustration, but it turned into something surprisingly powerful — a lightweight, zero-config way to turn real API traffic into working mocks in seconds.

If this sounds useful to you:
• 👉 Check it out on GitHub
• 🛠 Found an edge case or want to contribute? Pull requests welcome!
• 💬 I’d love to hear about your own mocking challenges or how you’re solving them

Mocking shouldn’t be a bottleneck. It should be one of the fastest parts of your development flow.

Let’s make it that way — together.

Related Work

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