One scans your dependencies, the other scans your code. You need both.
| SCA | SAST | |
|---|---|---|
| What it scans | Third-party libraries and dependencies | Your own source code |
| Finds | Known CVEs, license violations | Bugs, injection flaws, logic issues |
| Data source | Package manifests + vulnerability DBs | Source code or bytecode |
| Speed | Fast — just matching versions | Slower — full code analysis |
| False positives | Lower — CVE is either present or not | Higher — lacks runtime context |
| Languages | Package-manager aware (npm, pip, maven) | Language-specific analyzers |
| Shift-left fit | PR checks, lockfile monitoring | PR checks, IDE plugins |
Software Composition Analysis tools like Snyk, Dependabot, and Grype scan your dependency tree against known vulnerability databases. They're fast and accurate for known issues because CVE matching is deterministic — either you're running a vulnerable version or you're not. The gap is zero-days and vulnerabilities in your own code.
Static Application Security Testing tools like Semgrep, CodeQL, and Checkmarx analyze your source code for vulnerability patterns without running the application. They find injection flaws, hardcoded secrets, and unsafe API usage. The tradeoff is higher false positive rates and language-specific rule sets.
SCA catches the 80% of code you didn't write (open source dependencies). SAST catches bugs in the 20% you did write. Running both in CI gives you the broadest pre-production coverage. Add DAST for runtime issues neither can see.