SAST and DAST are both application security testing methods, but they examine software from very different perspectives. By analyzing source code or other code representations without running the application, SAST can identify potentially vulnerable code early in development. In contrast, DAST tests a running application from the outside and evaluates how it actually behaves at runtime.
The distinction matters because neither approach sees everything. SAST has access to the application’s internal code but lacks the complete runtime environment. DAST sees the application’s externally observable behavior but does not normally have access to its source code. Understanding that difference makes it easier to decide when to use each method—and why many security programs use both.
Quick Answer
SAST (Static Application Security Testing) analyzes source code, bytecode, or other code representations without executing the application. It is commonly used early in the software development lifecycle to identify insecure coding patterns and potential vulnerabilities.
DAST (Dynamic Application Security Testing) tests a running application from the outside by sending requests and analyzing its responses and behavior. It is typically used after an application has been built and deployed to a test, staging, or other accessible environment.
The main difference is simple:
SAST examines the application from the inside by analyzing its code; DAST examines the application from the outside while it is running.
NIST describes static analysis as code-based analysis independent of program execution and distinguishes it from execution-based dynamic analysis.
SAST vs DAST at a Glance
| Feature | SAST | DAST |
|---|---|---|
| Full name | Static Application Security Testing | Dynamic Application Security Testing |
| What it examines | Source code, bytecode, or other code representations | Running application |
| Application running? | No | Yes |
| Perspective | Internal / white-box | External / black-box |
| Source-code access | Required or normally available | Not required |
| Typical timing | Early development, pull requests, CI/CD | Testing after deployment |
| Main focus | Code-level security weaknesses | Runtime and externally observable weaknesses |
| Language dependence | Generally language/framework dependent | Generally language agnostic |
| Can pinpoint code? | Usually yes | Usually not |
| Typical benefit | Early detection and cheaper remediation | Real-world runtime validation |
| Main limitation | Limited runtime/environment context | Cannot directly inspect code paths it never exercises |
The exact capabilities vary between tools, but this distinction is consistently reflected in current application-security guidance and vendor documentation.
What Is SAST?
SAST stands for Static Application Security Testing.
SAST analyzes an application’s code without executing the application. Depending on the tool, the analysis may involve source code, bytecode, binaries, abstract syntax trees, control flow, data flow, or related representations.
The goal is to identify coding patterns or data flows that could create security weaknesses.
For example, a SAST tool may identify code in which untrusted input reaches a security-sensitive operation without appropriate validation or sanitization.
Common areas SAST may identify include:
- Injection vulnerabilities
- Unsafe handling of user input
- Hardcoded secrets or credentials
- Insecure cryptographic practices
- Dangerous function usage
- Certain cross-site scripting patterns
- Command-injection risks
- Security-sensitive coding mistakes
- Some authorization or validation weaknesses
The exact findings depend heavily on the scanner, programming language, framework, rules, and configuration. SAST is therefore best understood as code-focused security analysis, not as a guarantee that every vulnerability in an application will be discovered.
OWASP describes SAST tools as source-code or compiled-code analysis tools that can be integrated into development environments and repeatedly used during development.
Example of SAST
Imagine a developer writes:
user_input → string concatenation → SQL query
A static analyzer may recognize that untrusted input is flowing into a database query and flag the code for possible SQL injection.
Importantly, the application does not have to be running for the scanner to identify the potentially dangerous data flow.
What Is DAST?
DAST stands for Dynamic Application Security Testing.
DAST examines an application while it is running. Instead of reading the application’s source code, the scanner interacts with the application through its exposed interfaces, such as HTTP endpoints or APIs.
The tester or automated tool can send requests, manipulate inputs, inspect responses, and look for behavior that indicates a security weakness.
Depending on the application and tool, DAST can help identify issues involving:
- Authentication
- Authorization
- Session handling
- Input processing
- Runtime injection
- Cross-site scripting
- Security headers
- API behavior
- Configuration problems
- Unexpected application responses
- Other externally observable security weaknesses
GitHub describes DAST as testing programs while they execute, whereas SAST examines code when the application is not executing.
Example of DAST
Suppose an application has a login page at:
https://example.com/login
A DAST scanner can interact with that running application, submit requests, inspect responses, and test whether security controls behave as expected.
The scanner does not need to read the application’s PHP, Java, Python, JavaScript, or other source code to perform the external test.
That is one reason DAST is generally language agnostic.
What Is the Difference Between SAST and DAST?
The fundamental difference between SAST and DAST is what they observe.
SAST observes the application’s implementation.
DAST observes the application’s behavior.
Think of building a car.
SAST is like inspecting the engineering plans and components before the car goes onto the road.
DAST is like taking the finished car onto the road and checking how it behaves under real operating conditions.
Neither inspection replaces the other.
1. Static vs Dynamic
SAST is static because the application is not being executed during the primary analysis.
DAST is dynamic because the application is actively running while it is being tested.
NIST explicitly distinguishes code-based/static analysis from execution-based/dynamic analysis.
2. Inside vs Outside
SAST generally has access to the application’s internal implementation.
DAST approaches the application from the outside.
This is why SAST is often associated with white-box testing, while DAST is commonly described as black-box testing. GitLab uses this distinction in its comparison of the two approaches.
3. Early vs Later Testing
SAST can run very early. Developers can integrate it into an IDE, pre-commit workflow, pull request, or CI pipeline.
DAST requires a functioning application that it can interact with, so it normally occurs after the application has been built and deployed to an accessible environment.
That timing difference is one of SAST’s major advantages: problems can often be discovered before they move further through the development lifecycle.
4. Code Visibility vs Runtime Visibility
SAST can trace relationships inside code that DAST cannot directly see.
DAST, however, can observe behavior that depends on the actual runtime environment, configuration, deployed components, authentication flow, and external interactions.
This means a vulnerability may be visible to one approach but not the other.
5. Language Dependence
SAST tools generally need to understand the programming language or framework they analyze.
DAST interacts with the deployed application through its interfaces, so it generally does not care whether the backend was written in Python, Java, PHP, Go, C#, or another language.
GitLab specifically identifies language dependence as an important distinction between the two approaches.
What Can SAST Find?
SAST is particularly useful for identifying problems embedded in application code.
Examples include:
Hardcoded secrets
A scanner may flag credentials, API keys, or other sensitive values embedded directly in source code.
Injection risks
Static analysis can identify potentially dangerous data flows, such as user-controlled input reaching database or operating-system commands.
Insecure coding patterns
A SAST rule may identify a function or implementation pattern known to create security problems.
Weak cryptographic practices
Depending on the tool, SAST may identify inappropriate algorithms or insecure cryptographic implementations.
Unsafe data flows
Advanced static-analysis tools can trace how potentially untrusted data moves through an application.
However, a SAST finding does not automatically prove that an attacker can exploit the issue in the deployed application. Static analysis can lack runtime context and may therefore produce false positives. GitLab notes that SAST tends to produce more false positives because static analysis may not have all the contextual information needed to determine whether a suspicious code pattern is actually exploitable.
What Can DAST Find?
DAST is particularly useful for weaknesses that become visible only when the application is running.
Examples include:
Authentication weaknesses
DAST can test login and authentication behavior when appropriate access and configuration are provided.
Session problems
It can examine how the application handles sessions, cookies, and related runtime behavior.
Security-header issues
A deployed application may expose missing or incorrectly configured HTTP security headers that static code analysis cannot fully establish.
Runtime injection
DAST can send crafted inputs to an application and observe whether the application responds in a vulnerable way.
Access-control problems
When the scanner has the necessary authenticated contexts, dynamic testing can exercise endpoints and examine whether access controls behave as expected.
API vulnerabilities
DAST can interact with running APIs and analyze their externally observable responses.
The important qualification is that DAST can only test what it can reach and exercise. An application route that the scanner never discovers or triggers may remain untested.
When to Use SAST
Use SAST when you want to find security weaknesses as early as possible in development.
SAST is particularly valuable:
- While developers are writing code
- During pull requests
- Before merging changes
- In CI pipelines
- During regular development builds
- When enforcing secure coding policies
- When you want findings connected to specific code locations
For example, if a developer introduces an unsafe data flow today, a SAST scan can potentially identify it before the application is deployed.
This is the basic idea behind shift-left security: move security checks earlier in the development lifecycle.
NIST recommends performing static source-code analysis as soon as code is written because small pieces of code can be checked before the application is fully assembled.
When to Use DAST
Use DAST when you have a running application that you want to test from an external perspective.
It is particularly useful:
- After a build is available
- In QA environments
- In staging
- Before production releases
- During recurring security testing
- For testing deployed web applications
- For examining APIs and runtime behavior
- When runtime configuration is part of the security question
DAST is especially valuable because deployment can introduce variables that are difficult to understand from source code alone.
For example, the source code may appear secure while a production-like configuration exposes an endpoint incorrectly.
Can SAST and DAST Be Used Together?
Yes. In most mature application-security programs, SAST and DAST are complementary rather than competing alternatives.
SAST can identify potential problems inside the code.
DAST can test the application’s externally observable behavior.
Using both creates broader coverage because each method has a different viewpoint.
A simplified workflow might look like this:
Write Code
↓
SAST
↓
Build
↓
Deploy to Test/Staging
↓
DAST
↓
Security Review
↓
Production
Modern DevSecOps pipelines can include SAST, DAST, SCA, and other security checks at different stages. NIST’s DevSecOps guidance explicitly discusses integrating SAST and DAST testers into CI/CD pipelines.
SAST vs DAST in CI/CD
SAST is usually easier to place near the beginning of a CI/CD workflow because it does not require a deployed application.
For example:
Developer Commit
↓
SAST
↓
Build
↓
Unit/Integration Tests
↓
Deploy to Staging
↓
DAST
↓
Release
The exact pipeline depends on the organization’s architecture and risk tolerance.
The important principle is that security testing does not have to happen at only one stage.
SAST can provide early feedback, while DAST can provide runtime validation later in the pipeline.
GitLab recommends using DAST against a test environment and also describes its use for continuously testing running web applications.
SAST vs DAST vs SCA vs IAST
SAST and DAST are not the only application-security testing approaches.
| Method | Primary focus |
|---|---|
| SAST | Application code |
| DAST | Running application |
| SCA | Third-party/open-source dependencies |
| IAST | Runtime behavior with instrumentation |
| Penetration testing | Human-led adversarial testing |
SCA is especially important because an application can contain secure proprietary code while depending on a vulnerable third-party package. Sonatype distinguishes SAST as proprietary-code analysis, SCA as dependency-risk analysis, and DAST as testing running applications.
This is why SAST should not be treated as a replacement for every other security-testing method.
Common Mistakes With SAST and DAST
Mistake 1: Thinking SAST and DAST are interchangeable
They are not.
SAST examines code. DAST examines a running application.
Mistake 2: Assuming SAST proves an application is secure
It does not.
A SAST scan can identify potential weaknesses in code, but it does not reproduce every runtime condition or attacker interaction.
Mistake 3: Assuming DAST tests everything
It does not.
DAST depends on what the scanner can discover and exercise. Unreachable or untested functionality may remain outside its coverage.
Mistake 4: Thinking DAST can identify the exact source-code line
Normally, DAST identifies externally observable behavior rather than directly pointing to the underlying source-code location. GitHub notes this as an important DAST limitation.
Mistake 5: Choosing only one because it is “better”
There is no universal winner.
The two approaches answer different security questions.
Common Collocations
SAST
- SAST scan
- SAST tool
- SAST analysis
- SAST findings
- SAST pipeline
- SAST integration
- SAST testing
- static code analysis
- SAST vulnerability detection
DAST
- DAST scan
- DAST tool
- DAST testing
- DAST scanner
- DAST findings
- DAST pipeline
- dynamic security testing
- runtime security testing
- DAST assessment
Combined usage
- SAST and DAST
- SAST/DAST testing
- SAST and DAST integration
- SAST and DAST in CI/CD
- SAST and DAST security testing
Are SAST and DAST Interchangeable?
No.
They overlap in their overall goal—finding application security weaknesses—but they do not examine the application in the same way.
SAST asks questions about the implementation:
Does the code contain a potentially insecure pattern or data flow?
DAST asks questions about runtime behavior:
Can the running application be induced to behave in a vulnerable way?
Those are related questions, but they are not the same question.
How to Remember the Difference
Use this simple rule:
SAST = Source code.
DAST = Deployed application.
Or remember:
SAST sees inside. DAST tests outside.
If the software does not need to be running for the test, think SAST.
If the test requires a working application and sends requests to it, think DAST.
Which One Should I Use?
Use SAST when you want to inspect code before deployment.
For a running application, DAST is the better choice for testing runtime behavior.
Developers can also use SAST to receive security feedback early in the development process.
By contrast, DAST helps identify security issues that appear while an application is running.
For broader application-security coverage, combining SAST and DAST is usually the strongest approach.
A practical AppSec program may also add SCA, IAST, API testing, fuzz testing, or penetration testing depending on the application’s risks and requirements.
SAST or DAST? Practice Examples
Choose SAST or DAST for each situation.
- You want to inspect newly committed source code for insecure patterns.
- You want to test a deployed web application’s login behavior.
- You want to run a security check before a pull request is merged.
- You want to send crafted requests to a staging application.
- You want a scanner to identify a suspicious data flow in source code.
- You want to examine security headers returned by a live server.
- You want security feedback before the application is deployed.
- You want to test the externally observable behavior of an API.
Answers
- SAST — the source code is being analyzed.
- DAST — the running application is being tested.
- SAST — it can be integrated into the development workflow.
- DAST — the scanner is interacting with a deployed application.
- SAST — data-flow analysis is a code-analysis task.
- DAST — the actual HTTP response is being evaluated.
- SAST — static analysis can happen before deployment.
- DAST — the running API is being tested from the outside.
Frequently Asked Questions
What is the main difference between SAST and DAST?
SAST analyzes application code without executing it, while DAST tests a running application from the outside. SAST therefore provides internal code visibility, while DAST evaluates externally observable runtime behavior.
Is SAST better than DAST?
No. SAST and DAST serve different purposes. SAST is valuable for finding potential security weaknesses early in code, while DAST evaluates a running application’s behavior. Using both can provide more complete coverage.
Is DAST better than SAST?
No. DAST is not a replacement for SAST. It can find runtime issues that static analysis may not reveal, but it cannot directly inspect every part of the source code.
Does SAST require a running application?
No. SAST analyzes code or another static representation and therefore does not require the application to be running.
Does DAST require a running application?
Yes. DAST needs an accessible running application or service to test its behavior.
Which comes first, SAST or DAST?
In a typical development pipeline, SAST comes earlier because it can analyze code before deployment. DAST generally follows once a working application is available.
Can SAST and DAST find the same vulnerability?
Sometimes, yes. Their coverage can overlap, but they detect or validate weaknesses from different perspectives. A vulnerability that appears as a suspicious code pattern in SAST may also produce observable behavior during DAST testing.
Does SAST produce false positives?
It can. Static analysis may identify code that looks vulnerable without having all the runtime context needed to determine whether it is actually exploitable. The frequency depends on the tool and its configuration.
Can DAST find vulnerabilities in source code?
Not directly. DAST interacts with the running application and generally does not have access to the underlying source code.
Are SAST and DAST part of DevSecOps?
Yes. Both can be integrated into DevSecOps and CI/CD workflows at different stages. NIST’s DevSecOps guidance includes SAST and DAST among security testing activities that can be incorporated into CI/CD pipelines.
Conclusion
The difference between SAST and DAST comes down to perspective and execution. SAST analyzes application code without running the application, while DAST tests a running application from the outside. SAST is particularly useful for finding potential weaknesses early, when developers can address them close to the source. DAST is useful for evaluating real runtime behavior, deployed configurations, interfaces, and externally observable weaknesses.
The best choice is usually not SAST or DAST. They answer different security questions. A practical rule is simple: use SAST to examine the code early, and use DAST to test the running application later.
