Scanners differ by what they look at. Web application scanners, which OWASP also calls dynamic application security testing tools, probe a running site from the outside for problems such as cross-site scripting, SQL injection and insecure server configuration. Static analysis tools read source code. Dependency scanners compare your packages against published CVEs. Secret scanners search code and history for leaked keys. Most teams need more than one kind.
The value of a scanner is coverage and repetition. It checks hundreds of known patterns in minutes and can run on every change, which matters when an AI tool is rewriting large parts of your app in a single prompt. Something that was safe last week may not be after a regeneration.
Scanners also have limits. They report false positives that need a human decision, and they are weak at flaws in business logic, such as whether user A should be able to see user B's invoice, because the tool does not know your rules. Use scanning as a regular baseline, fix high-severity findings first, and combine it with manual testing of your access controls and a penetration test before handling sensitive data at scale.