Cypress Component Testing "dev-server: failed to start" in CI

Cypress component testing spins up a dev server (Vite or Webpack) to mount components. The run aborts at startup when the devServer framework/bundler is mismatched, the project’s build config is not found, or that config fails to compile.

What this error means

Component specs never start: Cypress reports "Cypress failed to start the dev server" with an underlying Vite/Webpack error. E2E specs are unaffected - only component testing, which needs the dev server, fails.

Cypress output

Cypress failed to start the dev server:

Error: Failed to resolve Vite config - could not load
/app/vite.config.ts (framework: 'react', bundler: 'vite')

Common causes

Framework/bundler mismatch or missing config

The component.devServer declares a framework/bundler that does not match the project (e.g. bundler: "webpack" with no webpack config, or vite without a resolvable vite.config).

Project build config fails to compile

The Vite/Webpack config the dev server loads throws (a bad plugin, a missing env, a TS error), so the server cannot come up and component testing aborts.

How to fix it

Point devServer at the right framework and config

cypress.config.ts

// cypress.config.ts
import { defineConfig } from 'cypress';
import viteConfig from './vite.config';
export default defineConfig({
  component: {
    devServer: { framework: 'react', bundler: 'vite', viteConfig },
  },
});

Fix the underlying build config

Read the nested Vite/Webpack error Cypress prints under the dev-server failure.
Confirm the bundler matches your app (vite vs webpack) and the config path resolves.
Ensure any env the config reads at load time is present in CI.

How to prevent it

Match devServer.framework/bundler to the project’s actual stack.
Reuse the app’s existing Vite/Webpack config for component testing.
Provide required env for the build config in CI.