Pa11y is an open-source automated accessibility testing tool designed to run from the command line or as part of an automated build process, making it a common choice for teams that want accessibility checks to run automatically every time code changes, rather than only during periodic manual audits.
Like other automated scanners, it is effective at catching a defined set of programmatically detectable issues but cannot evaluate subjective or context-dependent problems, which is why it works best as one layer of a testing strategy that also includes regular manual and screen reader testing.