A web application scanning tool probes a running application over HTTP the way an attacker would, and the real choice is between three shapes: open-source scanners you operate yourself (ZAP, Nuclei, Wapiti), interactive proxy suites for manual-plus-automated testing (Burp Suite), and managed DAST platforms that handle scheduling, authentication, and triage for you. The detection engines overlap far more than vendors admit; what you are actually buying at each tier is operational work you no longer do yourself.
This guide compares the options by the criteria that decide success in practice: coverage of authenticated surface, CI friendliness, triage burden, and cost of ownership.
First, place DAST correctly
Dynamic scanning is one of three complementary scan types, and teams get into trouble treating any one as complete:
- DAST (this post): tests the running app from outside. Finds injection, XSS, misconfigurations, auth flow bugs. Language-agnostic, no source access needed.
- SAST: a security code scan tool reads your source for dangerous patterns before anything runs. Finds bugs earlier, but drowns you in path-insensitive false positives without tuning.
- SCA: inventories your dependencies against advisory databases. Most real-world compromise paths in the last few years ran through this layer, not custom code — worth pairing any DAST rollout with dependency scanning.
A DAST finding is inherently credible (the scanner actually elicited the behavior over the wire), which is why DAST results tend to get fixed faster than static findings.
The open-source contenders
ZAP (ZAP by Checkmarx). The default free choice and a genuinely capable scanner: spider plus AJAX spider, passive and active rulesets, scriptable authentication, and packaged scan modes (baseline, full, API) that drop into CI as Docker one-liners. Since the core team moved to Checkmarx in 2024 the project has stayed open source and free. Weaknesses: single-page-app crawling requires care, authenticated scan setup is fiddly, and result management across runs is on you. Setup patterns are in our ZAP pipeline guide.
Nuclei. Not a general fuzzer but a template engine: thousands of community YAML templates matching specific known vulnerabilities, exposures, and misconfigurations. Extremely fast, very low false-positive rate, trivially CI-friendly. It will not find a novel XSS in your custom form, but it will tell you within seconds that you left a debug console exposed. Best used alongside a generic scanner, not instead of one.
Wapiti. A lean command-line black-box scanner covering the classic injection classes (SQLi, XSS, SSRF, XXE, file disclosure). Lighter than ZAP, fewer features, reasonable choice when you want a small dependency footprint.
Nikto. Server-configuration focused and showing its age, but still quick value on legacy stacks: dangerous default files, old server software banners, misconfigured methods.
The proxy suite: Burp
Burp Suite occupies a different niche: it is primarily a manual tester's instrument with automation attached. The free Community edition is an intercepting proxy with heavily throttled scanning; the Professional edition adds the real scanner and is priced per tester per year. If you have humans doing penetration testing, Burp Pro is close to mandatory equipment. If your goal is unattended scanning in a pipeline, Burp is the wrong shape — its strength is a human driving it, and its enterprise CI product is a separate, considerably more expensive purchase.
Managed DAST platforms
Hosted platforms (Safeguard's DAST product is one; Invicti, StackHawk, and Detectify are others in the space) converge on the same pitch: the engine is table stakes, the product is everything around it. Concretely that means:
- Authenticated scanning that keeps working. Recorded login flows, session management, and re-authentication handled by the platform rather than by your custom scripts that break every UI change.
- Scheduling and drift detection. Scans run on every deploy or on a calendar without a human remembering.
- Findings lifecycle. Deduplication across runs, regression detection ("this was fixed in March, it is back"), ownership routing, and ticket integration.
- Modern app support. JavaScript-heavy SPA crawling and API scanning from OpenAPI specs, which is where open-source crawlers struggle most.
Evaluate them on exactly those claims. Ask each vendor to scan your actual staging app behind your actual login during the trial; brochure detection rates mean nothing if the crawler cannot get past your auth.
Comparison at a glance
| Tool | Cost | Best at | Weakest at |
|---|---|---|---|
| ZAP | Free | Full-featured CI scanning | SPA crawling, findings management |
| Nuclei | Free | Known-issue detection, speed | Novel logic/injection bugs |
| Wapiti | Free | Lightweight injection testing | Coverage breadth, auth flows |
| Nikto | Free | Legacy server misconfig | Modern applications |
| Burp Suite Pro | Paid per tester | Manual + assisted testing | Unattended pipeline scanning |
| Managed DAST | Subscription | Authenticated, scheduled, triaged scanning at scale | Zero-budget teams |
How to choose without regretting it
- Count your authenticated surface. If more than roughly 80 percent of your app sits behind login (typical for SaaS), authenticated-scan reliability is your primary criterion and most tool comparisons written around unauthenticated scans are irrelevant to you.
- Decide who owns triage. A scanner without an owner produces reports nobody reads. If no one has hours budgeted weekly, buy triage workflow, don't just download an engine.
- Start free, measure the glue. Run ZAP plus Nuclei in CI for a month. If the maintenance of auth scripts, result diffing, and report routing stays under a few hours a month, you may never need to pay. When glue time exceeds that, a platform subscription is usually cheaper than the engineering time — compare against actual pricing rather than instinct.
- Demand API scanning. If you ship APIs (you do), spec-driven scanning from OpenAPI definitions gives better coverage than crawling ever will.
The failure mode to avoid is buying or deploying a scanner, pointing it at an unauthenticated marketing page, and declaring DAST "done." Coverage is the whole game.
FAQ
What is the difference between a web application scanning tool and a vulnerability scanner?
"Vulnerability scanner" usually refers to network/host scanners (Nessus, OpenVAS) that inventory services and known CVEs. Web application scanners speak HTTP to one application and probe its logic — different layer, different findings, both useful.
Is a security code scan tool a replacement for DAST?
No. SAST sees code paths DAST never reaches, and DAST sees deployment reality (headers, auth wiring, server config) that SAST cannot. Mature programs run SAST, DAST, and SCA together because their finding sets barely overlap.
Are free web application scanning tools good enough for compliance?
Often yes for the scanning requirement itself — SOC 2 and PCI DSS care that scans happen, get triaged, and get remediated on schedule. What free tools lack is the evidence trail; you will be assembling reports and remediation records manually.
How long should a scan take?
Baseline/passive scans: minutes. Full active scans: from twenty minutes to many hours, scaling with crawlable URLs and payload count. Runaway scan times usually indicate the spider is trapped in infinite URL spaces (calendars, search facets) and needs scope rules.