The best vulnerability scanner is the one that checks the things you run: a network scanner for servers and devices, a web scanner for sites and APIs, or a template scanner for engineers. Free options exist for each. This page lists ten in no particular order and shows how to sort the results so the dangerous ones come first.
A scanner doesn't fix anything. It hands you a list, sometimes a very long one, and the real work starts there: deciding which findings matter this week and which can wait. So the tool you want is one whose results your team can read and act on, not the one that finds the biggest pile of issues.
Here are ten scanners in no particular order, listed alphabetically, covering open source projects, free tiers and demo-led products. Each description comes from the tool's own website, re-checked today. Two of them have changed names recently, and I've noted the former names so you can match them to older articles and forum threads.
I've written this for small business owners, IT leads and developers who look after their own systems, so it's plain English and focused on what to ask before you trust a report.
Scanners compared at a glance
In the free plan column, Yes means the tool's own site describes a free plan, free edition or open source version, Trial only means a time-limited or restricted licence, and No means you're pointed to a demo.
| Tool | Type | Good for | Free plan |
|---|---|---|---|
| Burp Suite | Web security testing toolkit | Manual web testers learning security | Yes |
| Detectify | Web and attack surface scanner | Developers wanting crowd-sourced checks | Yes |
| Intruder | Cloud vulnerability scanner | Small teams scanning internet-facing systems | Yes |
| Invicti Web + API | Web and API scanner | Teams scanning web apps and APIs | No |
| Nessus | Network vulnerability scanner | Learning and home lab scanning | Trial only |
| Nuclei | Open source template scanner | Engineers writing custom detection templates | Yes |
| OpenVAS | Open source network scanner | Network scanning with an open source engine | Yes |
| Pentest-Tools.com | Online scanner toolkit | Consultants running quick scans online | Yes |
| Probely | Web and API scanner | Small teams scanning a single web app | Yes |
| ZAP | Open source web app scanner | Free web app security testing | Yes |
Ten vulnerability scanners for small teams
Burp Suite
Best for: Penetration testers and students who want a manual web testing toolkit, starting with the free Community Edition and upgrading later.
Detectify
Best for: Developer-led teams who want automated web and attack surface scanning, with checks informed by ethical hackers, starting on a free tier.
Intruder
Best for: Small teams without a dedicated security hire who want continuous scanning of internet-facing systems, beginning on a free plan.
Invicti Web + API
Best for: Formerly known as Acunetix, this is for application teams who want an established web and API scanner, bought through a demo.
Nessus
Best for: Students and home lab users learning network scanning; the Essentials licence lasts 30 days and is for non-commercial or personal use only.
Nuclei
Best for: Engineers who want to write or reuse community detection templates and run fast checks against known vulnerabilities.
OpenVAS
Best for: Teams who want a full-featured network scanner with an open source community edition and a daily-updated test feed.
Pentest-Tools.com
Best for: Consultants who want browser-based network, website and WordPress scanners with branded reports, starting on a free edition.
Probely
Best for: A small team scanning one web app or API on a free plan before adding more targets.
ZAP
Best for: Developers new to security who want a free, open source web app scanner; it was previously called OWASP ZAP.
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Sorting findings by what attackers already use
This is the part most scanner round-ups skip. CISA, the US Cybersecurity and Infrastructure Security Agency, keeps a Known Exploited Vulnerabilities catalogue, which it describes as the authoritative source of vulnerabilities that have been exploited in the wild. CISA says organisations should use it as an input to how they prioritise vulnerability management, and it publishes the list as CSV and JSON files.
What that means for you: when a scan returns hundreds of findings, the ones on that list go to the top, because someone is already using them. Ask each vendor whether their scanner flags known exploited issues, or whether you'll need to cross-check the list yourself. It's a simple filter that turns an overwhelming report into a short to-do list you can get through.
Network, web or template scanning
- Network scanners look at servers, laptops, routers and other devices for missing patches and weak settings.
- Web and API scanners crawl your site or app looking for issues such as injection flaws and exposed data.
- Template scanners run small, specific checks written by a community, which engineers can extend.
- Manual toolkits help a tester probe a site by hand, which finds things automated scans miss.
If injection flaws are new to you, this plain-English explainer on SQL injection shows why web scanners look so hard for them.
Running your first scan safely
- Write down what you own: domains, IP addresses, web apps and APIs.
- Get written permission for anything hosted by someone else before you scan it.
- Start with a light scan outside busy hours, so you don't slow a live site.
- Sort the results, putting known exploited issues and internet-facing systems first.
- Fix, then rescan to prove the fix worked.
- Schedule regular scans so new issues don't sit unnoticed.
Where scanners fall short
- False positives. Some findings won't apply to your setup, so someone has to check before you panic.
- Logged-in areas. A web scanner that can't sign in won't see most of your app.
- Business logic. Scanners rarely spot a checkout that lets someone change an order total.
- One-off scans. A clean report today says little about what changes after your next release.
For deeper checks, my round-up of tools testers use for penetration testing covers the kit that goes beyond automated scanning.
Do you make vulnerability scanning software? Tool makers can ask to be considered for a featured place on this list.
My plain advice before you pick a scanner
Match the scanner to what you run. If your main exposure is a website or app, start with a web scanner on a free plan and scan one target thoroughly. If you've got an office network and servers, an open source network scanner is a sensible first step, as long as someone can read and act on the results.
Whatever you choose, don't measure success by the number of findings. Measure it by how quickly the serious ones get fixed. And never scan systems you don't own or haven't got permission to test; that's a quick way to fall out with your host or a partner.
Frequently asked questions
What does a vulnerability scanner do?
It checks your systems, sites or apps for known weaknesses, such as missing patches or risky settings, and gives you a list to fix.
Is a vulnerability scan the same as a penetration test?
No. A scan is automated and broad. A penetration test is a person trying to break in, which finds issues a scan can't.
Are free vulnerability scanners any good?
Several open source and free-tier scanners are widely used. The limits tend to be in targets, reporting and support rather than the core checks.
How often should I run a vulnerability scan?
Regularly, and after any big change to your site or network. Many tools can schedule scans so nobody has to remember.
Which findings should I fix first?
Start with issues known to be exploited in the wild, which CISA lists in its Known Exploited Vulnerabilities catalogue, then anything facing the internet.
Can I scan a website I don't own?
Not without written permission. Scanning other people's systems can break their terms and the law.
