The axe browser extension (for Chrome and Firefox) is an immensely helpful tool for auditing web pages for accessibility defects. This extension is powered by the same rules engine developed by Deque Labs in their axe-core open source library which also powers the react-axe development tool. Each reported defect offers a ton of information about the defect, why it's a problem, severity level, groups impacted and ways to fix the defect. This can be a great resource for learning more about how to write accessible code.