SAST, DAST and SCA: which scanner do you actually need

Ask three vendors what security scanning you need and you’ll get three different answers, each one conveniently matching the tool they sell. The reality is simpler. There are three kinds of scanning, they catch different problems at different points, and a small team rarely needs all of them at full strength on day one.

SAST: scanning the code you wrote

Static application security testing reads your source code without running it. It looks for patterns that lead to vulnerabilities — unsanitised input, hard-coded secrets, risky function calls.

Because it runs on code, it works before the application is even built. That’s its real value: the issue is caught in the pull request, while the developer still has the file open. The cost is false positives. SAST tools flag things that aren’t real problems, and if you don’t tune them, developers learn to ignore the noise.

SAST is the one to start with. It’s cheap, it runs early, and it teaches developers security habits.

DAST: attacking the running application

Dynamic application security testing runs your application and attacks it from the outside, the way a real attacker would. It doesn’t care how the code is written — it tries to break the running system: injecting input, tampering with requests, finding misconfigurations.

DAST catches the problems SAST can’t see, because they only exist when everything is wired together: a misconfigured server, an endpoint that should require authentication but doesn’t, a data flow that leaks information at runtime.

The cost is that it needs a running application, so it happens later — typically against a staging environment before release. And it can’t see inside the code, so fixing what it finds often means hunting for the cause.

SCA: scanning the code you didn’t write

Software composition analysis looks at your dependencies. Most of a modern application is libraries you didn’t write, and a known vulnerability in one of them is a vulnerability in your product.

SCA checks your dependency list against databases of known vulnerabilities and tells you what to upgrade. It’s fast, it’s concrete, and it’s usually the highest ratio of real findings to noise. If you only adopt one thing this quarter, adopt this.

How to choose

The decision isn’t really “which one” — it’s “which one first, and how much of each.”

If your priority is…	Start with	Because
Catching issues early in development	SAST	It runs on pull requests, before merge
Finding real-world holes before release	DAST	It attacks the running system
Fixing known risks in dependencies	SCA	It’s the highest-signal, lowest-effort scan
Passing a customer security review	DAST + SAST	Reviewers expect both, with reports

A pragmatic sequence: start with secret scanning and SCA, because they’re cheap and high-signal. Add SAST on pull requests once you can tune the rules. Add DAST against staging once you have something worth attacking. For most small teams, that’s the whole roadmap, and each step is small enough to finish without slowing shipping.

Our SAST scanner checks each pull request, and our DAST scanner tests running applications before release. Both feed findings into a single register through the GRC Platform. If you’d rather not run them yourself, DevSecOps & Security Tooling adds and tunes them for your codebase.