Every frontend developer knows this feeling.
The backend isn't ready. You've got a Figma file, a deadline, and absolutely nothing to call. So you do one of three things:
Hardcode JSON directly into your component. Spin up json-server locally. Or just wait.
All three are painful in different ways.
The real problem with existing mock tools
The tools that exist today fall into two camps.
Too heavy. MSW is powerful but requires install, config, and service worker setup. Mockoon is great but it's a desktop app — your mock lives on your machine, nobody else can use it. MirageJS requires you to essentially rebuild your API layer inside your frontend.
Too simple. Most online mock tools give you a JSON endpoint but nothing else. No error simulation. No latency. No way to test what happens when your API is slow or broken.
Neither camp solves the actual problem: I need a working API URL my whole team can hit in under a minute, without setting anything up.
What frontend devs actually need
Think about the real workflow:
Designer hands off a screen
Frontend dev needs to build it
Backend endpoint doesn't exist yet
Frontend dev is blocked
What unblocks them isn't a perfectly architected mock system. It's a URL that returns the right shape of data, right now, that they can share with a teammate without any setup.
That's it.
The gap nobody was filling
When building my own projects I kept running into the same wall. I didn't want to install anything. I didn't want to write config files. I didn't want a mock that only lived on my laptop.
I also wanted to test the hard stuff — what does my UI do when the API takes 3 seconds to respond? What happens when it fails 30% of the time? These are real production scenarios that most mock tools completely ignore.
Intermittent failures especially. Every tool lets you set a mock to always return 500. But real APIs don't always fail — they fail sometimes. Testing retry logic means you need a mock that fails 1 in 3 requests. I couldn't find anything that did this simply.
So I built mockserver.in.
How it works
Three ways to create a mock:
Plain English — Type "return a list of 5 products with name, price, and image URL." It generates the JSON and gives you a live URL instantly.
JSON editor — Paste your own response body, set your status code, done.
Form — Fill in fields if you prefer structured input.
Every mock gets a shareable URL immediately. No account needed to get started.
Then you can layer on:
Fixed or random latency
Specific HTTP status codes
Intermittent failure rates — "fail 20% of requests"
Timeout simulation
Your frontend hits a real URL. Your mobile team hits the same URL. No one needs to run anything locally.
Who this is for
Frontend devs blocked by missing backend endpoints
Mobile devs who need a stable URL during development
Teams where backend and frontend work in parallel
Anyone who wants to test loading states, error handling, and retry logic without touching the backend
Try it
mockserver.in — free for 20 mocks, no credit card, no setup.
Describe your endpoint and get a URL in 30 seconds.
Top comments (0)