SAST reads the blueprints, DAST tries the doors of the finished building, and IAST puts sensors inside while people walk through. Each finds different problems, none finds everything, and a manual review of how the business logic works still matters. That is the one minute version for a budget holder.
SAST: reading the blueprints
Static analysis examines code without running it. OWASP describes it as examining source or compiled code for security flaws. It is cheap to repeat, runs on every change and points to the exact line.
The honest caveat for executives: it produces false alarms, and it misses problems that depend on how the business rules are meant to work. Budget developer time to sort through results.
DAST: trying the doors
Dynamic testing treats the running application like an outsider would. The OWASP DevSecOps Guideline calls it black-box testing: it sends malicious inputs to the live app to see what breaks. It needs no source code and can run on a schedule.
Caveat: it needs a running test environment, it can be slow, and it can only report what it can reach from outside.
IAST: sensors inside the building
Interactive testing places sensor modules inside the application. While tests or people use the app, the sensors watch what happens and report problems. The guideline describes feedback as near real time.
Caveat: it needs the sensors installed and it only sees what gets used. If your automated tests cover little, it learns little.
What none of them replace
The OWASP testing guide says automated tools are generic and that serious issues often hide in custom business logic. A human tester can try to misuse a feature the way a customer or attacker would. Ask for that on the high-value flows, such as payment and login.
What to ask them to fund
Frame it as a few concrete decisions.
- Time, not just tools. A scanner without someone to read the output is shelfware.
- A pilot on real repositories before a contract.
- A staging environment that mirrors production, so dynamic testing is meaningful.
- A periodic manual test of the riskiest flows.
What to ask for in return
Ask for three numbers each quarter: how much of the code is scanned, how long serious findings stay open, and how many serious findings were found before release versus after. Those tell you whether money is turning into fewer incidents.
A one sentence summary
Use cheap automated checks all the time, add environment-level checks when you have the environment, and pay for human testing where a single flaw would hurt most.
Quick check
Which one should we buy first?
For most teams, static analysis on pull requests and dependency scanning, then dynamic testing against staging.
Can one tool do all three?
Some products bundle them, but they remain different techniques with different setup needs. Check each one in a pilot.
Sources
- Source code analysis tools, OWASP Community
- DAST, OWASP DevSecOps Guideline
- IAST, OWASP DevSecOps Guideline
- OWASP Web Security Testing Guide
Last reviewed: 19 October 2026.
