LABS
Service Worker API Mocker
Stop writing custom mock backends. Define your API JSON responses here and generate a secure injection script that mocks fetch calls instantly in your browser.
Service Worker API Mocker (Local-First)
Define your mock API routes below. We will generate a secure, dependency-free Monkey-patch script that intercepts window.fetch in your app. 100% Zero-Server. No Node.js backend required.
Generated Injection Script
// Paste this in your browser console or top-level React/Next.js layout
(function() {
const originalFetch = window.fetch;
const mockRoutes = [
{
"method": "GET",
"path": "/api/users",
"response": "{\n \"status\": \"success\",\n \"data\": []\n}",
"delay": 500
}
];
window.fetch = async function(url, options) {
const method = (options?.method || 'GET').toUpperCase();
const routeUrl = typeof url === 'string' ? url : url.url;
const matchedMock = mockRoutes.find(r =>
routeUrl.includes(r.path) && r.method === method
);
if (matchedMock) {
console.log(`%c[Castov Mock Server] Intercepted ${method} ${r.path}`, 'color: #8b5cf6; font-weight: bold;');
if (matchedMock.delay > 0) {
await new Promise(res => setTimeout(res, matchedMock.delay));
}
return new Response(matchedMock.response, {
status: 200,
headers: { 'Content-Type': 'application/json' }
});
}
return originalFetch.apply(this, arguments);
};
console.log("%c[Castov Mock Server] Installed and listening for fetch requests!", "color: #10b981; font-weight: bold; font-size: 14px;");
})();Local API Mocking
Intercept fetch calls without a backend.
How to use this tool
- Define your routes
- Copy the script
- Paste into your browser console or layout file.