Applitools

It is a set of web developer tools built directly into the Google Chrome browser. It can help you edit pages on-the-fly and diagnose problems quickly, which ultimately helps you build better websites, faster

Catch visual bugs in static & dynamic UI components with Percy. Ensure your website’s UI reliability in dynamic environments. Detect and resolve bugs at speed for each component across browsers and viewports.

It lets you create and manage UI tests that check specific functionality in your website or application. We execute these automated browser tests continuously from the cloud and alert you if anything breaks.

It is a modified browser built using Electron that helps in responsive web development. Preview all target screens in a single window side-by-side. Brings down your development time. Use your already-familiar dev-tools from the browser. No additional learning curve.

Requestly is a lightweight proxy available as a browser extension & desktop app to intercept & modify network requests. Using Requestly you can Modify Headers, Redirect URL, Mock API response, Delay/Throttle requests, etc.

It is a Screenshot Testing service. It will connect your existing Android, iOS or Selenium tests to track how screenshots change over time, notifying you on Pull Requests, Jira etc.

It is an open-source and cross platform Web debugging proxy. You can capture network request & response. It is available for macOS & Windows.

One-click full-site HTML validation, CSS validation, JavaScript static analysis and broken link checking.