I was tired of json-server — so I built a free mock API tool (no signup needed)

#javascript #python #webdev #productivity

Every frontend project I start hits the same wall.

I have a UI to build. I know what the API responses should look like. But the backend isn't ready yet.

So I spend 15–20 minutes doing the same setup ritual:

npm install -g json-server
# create db.json
# configure routes
# run json-server --watch db.json --port 3001

And that's the fast version. If I need CORS headers, custom status codes, or simulated delay, it gets longer.

I built MockBolt to remove that setup time entirely.

What MockBolt does

Paste JSON → click Generate → get a live public API URL.

That's it. No npm install. No terminal tab. No local port.

curl https://mockbolt.com/b/7f3d2c1a-9b8e-4f5a-b6d0-3e2c1f4a8b7d
# returns your JSON immediately

The endpoint:

Supports all HTTP methods (GET, POST, PUT, PATCH, DELETE)
Returns your JSON with the right status code
Has open CORS — works from any browser origin
Accepts custom response headers
Can simulate latency up to 10 seconds

Each mock gives you two URLs:

Public URL — share this with your frontend or teammates
Management URL — keep this private; edit payload, status code, methods, and delay anytime

No account. No email. No credit card. Free for 24 hours.

A real example

Say I'm building a frontend that needs a /users endpoint but the backend isn't ready. In MockBolt:

1. Paste this JSON:

{
  "users": [
    { "id": 1, "name": "Alice", "role": "admin" },
    { "id": 2, "name": "Bob", "role": "viewer" }
  ],
  "total": 2
}

2. Select GET, click Generate Endpoint

3. Get a URL like https://mockbolt.com/b/e8bdb0ce-8ed9-44a8-adcc-b0af6a054443

4. Hit it immediately:

curl https://mockbolt.com/b/e8bdb0ce-8ed9-44a8-adcc-b0af6a054443
# {"users":[{"id":1,"name":"Alice","role":"admin"},{"id":2,"name":"Bob","role":"viewer"}],"total":2}

Done in under 30 seconds.

Testing error states and slow responses

MockBolt lets you set any status code from 100 to 599 and add a response delay.

Want to test how your app handles a 503 Service Unavailable? Set the status code, generate the endpoint, point your error-state tests at it.

Want to test loading spinners and skeleton screens? Set a 2000ms delay.

The copy-as-code panel also generates ready-to-run snippets in curl, fetch, axios, and Python requests — paste directly into your test file.

How I built it

Stack:

Backend: FastAPI (Python) + PostgreSQL
Frontend: React + TypeScript + Vite + Tailwind CSS
Deployed on AWS Lightsail behind Cloudflare

A few interesting decisions along the way:

Rate limiting behind Cloudflare — slowapi needs to read CF-Connecting-IP instead of request.client.host (which returns the Docker bridge IP behind Nginx). Took a couple of iterations to get this right.

Hit count accuracy — early on the counter was off because Cloudflare was caching GET responses. Fixed it with aggressive cache-busting headers: Cache-Control: no-cache, no-store, must-revalidate, max-age=0.

Anonymous management — instead of accounts, each mock gets a UUID secret token as the only credential. Tradeoff: if you lose the management URL you can't recover it. But it removes signup friction entirely and means zero user data to protect.

What's next on the roadmap

OpenAPI/Swagger import — paste a spec, get mock endpoints for every path automatically
URL prefill — mockbolt.com/?template=auth so blog posts can link to a live editable example
Multiple endpoints — one mock ID that serves different JSON per path (e.g. /users and /products)