It’s best to get someone to perform manual testing (hands on with a screen-reader, etc). But you can try using the AIM wave tool (just google it), for some possible pointers. That tool might not be able to test what you’re developing however, and is only a basic substitute for manual testing.

I’ve done testing for several years, and may be able to assist. Just FYI.

I’m afraid you can’t fully automate it. Which is a slight downside if you wanted to build it into a CI pipeline. The Wave tool that was mentioned is a good start though. But like the other commenters have said, I would highly recommend a manual test. Even manual tests can be a little subjective, it depends on the person in question.And their level of experience.But they will catch many things that a tool just would not. Best of luck, and I hope this is helpful

Compliance Professional here. As others have said, there is no way to confirm WCAG2.1 level aa conformance with automated testing alone. Are you building a website?

It is pretty much guarantee that there is absolutely no way to 100% assess compliance, because many of the criteria are subjective. To give a trivial example, how can a tool know that your images have meaningful text alternatives? Not just any alternative but one which will actually be useful?
In general I've seen estimates that about 30% give or take of the testing can be done via automated means, the rest requires human judgement.

We are building a tool to no code create and publish website, with drag n drop, configurations.

This website will probably help you decide the best tool.
But as others have pointed out, manual testing is the superior option and will catch things that tools just never will.
https://www.w3.org/WAI/ER/tools/?q=wcag-21-w3c-web-content-accessibility-guidelines-21&q=wai-aria&q=css&q=xhtml&q=html&q=images&q=providing-step-by-step-evaluation-guidance&q=groups-of-web-pages-or-web-sites&q=restricted-or-password-protected-pages