The Tool Desk
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What do SAST, DAST, IAST and SCA mean?
Application security testing is an umbrella term for methods that examine different parts of a software system. The main distinction is what evidence a check can see: code before execution, components used to build the application, or behavior while the application runs.
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| Method | What it examines | Car analogy | Key visibility limit |
|---|---|---|---|
| SAST (static application security testing) | Source code or related artifacts without running the application | Review the design and build plans | Does not observe live application behavior |
| SCA (software composition analysis) | Third-party libraries and components used by the application, including known vulnerabilities | Inspect the parts list and suppliers | A component check does not prove the whole application is secure |
| DAST (dynamic application security testing) | A running application, tested from the outside | Take the assembled car out for a road test | External interaction does not reveal every internal code path |
| IAST (interactive application security testing) | A running application observed from within as tests or other activity exercise it | Instrument the car during a test drive | Findings depend on exercised behavior and supported instrumentation |
These analogies are illustrations of the methods’ technical differences, not exact equivalents. No one category sees every risk source, and a combination of checks does not by itself guarantee security. OWASP’s IAST guidance describes IAST as an instrumented running-application approach, while its DevSecOps overview covers a broader set of testing categories.
How does each method fit into development?
Checks can be placed at different points in a development workflow, depending on the evidence they need. OWASP’s Security Testing guidance gives an example workflow: SAST, secrets scanning and infrastructure-as-code checks at commit time; SCA and image scanning at build time; and DAST at deployment against a running application. This is an example of placement, not a mandatory schedule for every team.
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- Before execution: SAST can inspect code early, and secrets or IaC checks can examine repository changes or infrastructure definitions.
- During the build: SCA can check the third-party components included in the application.
- Against a running application: DAST probes from outside; IAST observes from within when application behavior is exercised.
Actual timing varies with the application and workflow. API security testing is also a distinct area in OWASP’s DevSecOps overview; it should not be treated as simply another name for DAST.
What does each check reveal—and what does it miss?
SAST: inspect code before it runs
SAST analyzes source code or related artifacts without observing the live application. In the car analogy, it is like reviewing plans for risky design or assembly patterns before the vehicle is on the road. Its early access to code is useful, but it cannot show how the application behaves at runtime.
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SCA: check the components you rely on
Applications often use third-party libraries. SCA checks those components, including for known vulnerabilities; the car equivalent is examining the parts list and suppliers. It provides evidence about dependencies, not proof that the application’s own code or overall behavior is safe.
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DAST: test externally visible behavior
DAST interacts with a running application from the outside and observes its responses. Like a road test, it can reveal how the assembled system responds to external interaction. But driving the car does not expose every internal mechanism, and probing an application externally does not mean every code path has been examined.
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IAST: observe exercised behavior from inside
IAST instruments a running application and observes it from within while activity exercises it. The OWASP Foundation’s DevSecOps Guideline says: “Interactive Application Security Testing combines the strengths of static and dynamic analysis by instrumenting the running application — typically with an agent inside the runtime — and observing it from the inside while it executes.” In the car analogy, this is an instrumented test drive.
IAST visibility depends on what tests or other activity actually exercise, as well as supported runtimes and instrumentation. An installed agent does not establish that an unvisited path was tested. OWASP’s IAST comparison also discusses timing, visibility, source-code needs, fix guidance and CI integration effort as ways to distinguish implementations.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Where do secrets scanning, IaC and API testing fit?
These related checks broaden the view beyond the four main acronyms; they are not synonyms for SAST.
- Secrets scanning checks repositories or configuration for exposed sensitive values, such as credentials or API keys. In the car analogy, it is like checking where the keys are handled.
- IaC (Infrastructure as Code) refers to infrastructure described in files or code. Checking those definitions early is like inspecting the factory setup before production.
- API security testing examines API surfaces as a distinct testing area. It should not be silently folded into DAST, even though a DAST tool may interact with an application’s exposed interfaces.
OWASP places secrets scanning and IaC analysis among commit-time activities in its workflow guidance, and identifies API security as a related area in its DevSecOps overview.
How should you compare testing approaches?
Choose by the evidence you need and the point in the workflow where it can be collected—not by treating one acronym as a universal replacement for the others. When assessing tools or a testing plan, ask:
- Timing: Can the check run when code or dependencies change, during the build, or only after deployment?
- Access: Does it need source code, a running application, an agent in the runtime, or a dependency inventory?
- Visibility: Does it examine code, components, externally observable behavior, or instrumented execution?
- Coverage: Which code paths and application behaviors are actually exercised?
- Investigation context: What evidence helps a developer understand and investigate a result?
- Integration: What setup is required for the team’s CI workflow and supported languages or frameworks?
Category labels do not establish that every tool works alike. OWASP’s comparisons offer practical evaluation dimensions, but the official category-level material does not establish universal numerical claims about accuracy, false-positive rates, cost or breach reduction.
What the car analogy can—and cannot—tell you
The analogy is useful for remembering that application security checks inspect different things: plans, parts, external behavior and instrumented operation. Its limit is just as important: software checks analyze code, dependencies or application behavior, not a physical vehicle. Passing one inspection—or having one kind of instrument installed—does not establish that every risk has been found.
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