Your build passes. The new feature works. But its button looks different from the rest of the app, the heading uses a new font size, and the page scrolls sideways on a phone.
These problems show up in code written by people and AI alike. As changes arrive faster, it gets harder to check every screen and remember every component the project already has.
Design Bug Bot adds UI review to your GitHub workflow. It examines changes against your project's components, styles, and rendered UI, then explains the issues it finds and suggests code to address them.
What it looks for
- Components that should be reused. A new button or card may duplicate an existing component. The bot looks for compatible components and variants in your repository before recommending another implementation.
- Inconsistent typography and styling. A one-off font, text size, or style can make one screen feel disconnected from the rest. The review compares changes with patterns already used in the project.
- Layouts that break on mobile. Fixed widths, horizontal overflow, and hidden actions can survive a desktop check. When rendering is available, the bot inspects desktop and mobile views.
- Performance concerns with evidence. Heavy resources or repeated React renders can affect the interface. Performance findings require measurements, rather than guesses about whether a change is slow.
A review you can act on
A finding explains the problem, identifies the relevant file and line when available, and describes a suggested fix. Code suggestions give you something concrete to inspect, copy into your editor, or hand to a coding agent.
For example, a mobile layout issue might lead to a change that lets a container shrink. A consistency issue might point you to the button your project already uses. The aim is to make the next edit clear without making you translate a vague design comment into code.
Reviews can include screenshots when the app renders successfully. If rendering is unavailable, the bot can still report issues supported by source code and offer code proposals, clearly marked as not visually verified. You review and test those changes before applying them.
Fits your existing workflow
Connect GitHub in 21st, choose your repositories, and enable pull request reviews. Read the results in GitHub or open the full review in 21st. You can also review recent changes on the default branch manually, after a chosen number of commits, or on a schedule.
For a solo developer, it adds another check before shipping. For a designer, it connects UI feedback to the code that needs attention. For a team, it helps keep contributions consistent as more people work on the same product.
Design Bug Bot is included with 21st AI. All paid plans can try five successful reviews free within seven days of the first review. After the trial, reviews use AI credits on an AI-enabled plan. See the trial and billing details.