Are there any responsive design testing tools that focus on checking UI consistency across desktop, tablet, and mobile breakpoints?

Yes — there are several tools that are specifically useful for checking UI consistency across desktop, tablet, and mobile breakpoints. A few popular options:

Visual regression / responsive testing tools

• Percy
  Captures screenshots at different viewport sizes and highlights visual differences. Good for checking whether layouts stay consistent across breakpoints.

• Chromatic
  Especially popular with Storybook users. Great for testing component and layout changes across multiple screen sizes.

• Applitools
  AI-powered visual testing that can compare UIs across devices and breakpoints, useful for catching subtle inconsistencies.

• BackstopJS
  An open-source visual regression tool where you can define multiple viewport sizes and compare screenshots over time.

Browser/device testing platforms

• BrowserStack
  Lets you test real devices and browsers at desktop/tablet/mobile sizes. Good if you want to validate behavior beyond screenshots.

• LambdaTest
  Similar to BrowserStack, with cross-browser and responsive testing across many viewport/device combinations.

• Sauce Labs
  Provides real-device and browser testing, useful for verifying layout consistency and responsiveness.

Built-in browser tools

• Chrome DevTools Device Mode
  Not a dedicated consistency checker, but very useful for quickly previewing desktop/tablet/mobile breakpoints.

Good use cases

If your goal is:

• Compare the exact UI visually across breakpoints → Percy, Chromatic, Applitools, BackstopJS
• Test on actual devices/browsers → BrowserStack, LambdaTest, Sauce Labs
• Quick local breakpoint checks → Chrome DevTools

If you want, I can also suggest the best tool based on your stack (React, Vue, plain HTML/CSS, Storybook, etc.) or give you a short comparison table.