Free Website Security Scanner Tools Compared (2025)
Free Website Security Scanner Tools Compared (2025)
I've tried probably a dozen security scanners over the years. Some are great at one thing, useless at others. Some require signup for basic features. Some give you a score with no explanation of what's actually wrong.
Here's my honest breakdown of the free tools worth using, what each one does well, and when to use which.
The Quick Answer
If you only want to run one tool: use DomainOptic (yeah, that's us - but I'm saying this because I built it specifically to solve the problems I had with other scanners). It checks SSL, DNS, security headers, blacklists, and exposed secrets in one scan. No signup.
If you need really deep SSL analysis: Qualys SSL Labs. It takes 2-3 minutes but gives you everything.
If you just want to check headers: SecurityHeaders.com. Quick and simple.
Comparison Table
| Tool | SSL | DNS/Email Auth | Headers | Secret Scanning | Blacklist | Needs Signup |
|---|---|---|---|---|---|---|
| DomainOptic | Yes | Yes | Yes | Yes | Yes | No |
| SecurityHeaders.com | No | No | Yes | No | No | No |
| Mozilla Observatory | Basic | No | Yes | No | No | No |
| Qualys SSL Labs | Very Deep | No | No | No | No | No |
DomainOptic (What We Built)
I'm biased, obviously. But here's why I built this: I was tired of running 4 different tools to check one website. SSL Labs for certs. SecurityHeaders for headers. MXToolbox for DNS. Then manually checking for exposed API keys.
So we combined everything:
- SSL certificate status, expiration, protocol versions
- DNS health including SPF, DKIM, DMARC (the email authentication stuff Gmail requires)
- All the security headers with a letter grade
- Blacklist checks
- Secret scanner that actually looks at your JavaScript for exposed API keys
That last one is big. GitGuardian reported 12.8 million secrets leaked on GitHub in 2024. Most scanners completely ignore client-side JavaScript where keys often end up.
The scan takes about 20 seconds. No signup required. Try it here.
SecurityHeaders.com
Scott Helme's tool. It's been around for years and it does one thing well: check your HTTP security headers and give you a grade.
No SSL checking. No DNS. No secret scanning. But if you just want to know "do I have HSTS? what about CSP?" - it's quick and easy.
Mozilla Observatory
Mozilla's take on security scanning. Checks headers and gives you a score. The scoring is a bit opinionated (it really wants you to have a strict CSP), but the explanations are good.
Doesn't check SSL configuration or DNS. Doesn't scan for secrets.
Qualys SSL Labs
The gold standard for SSL/TLS analysis. If you want to know every single detail about your certificate, cipher suites, protocol support, and potential vulnerabilities - this is it.
The downside: it's slow (2-3 minutes per scan) and it only checks SSL. No headers, no DNS, no secrets. Use it when you need deep SSL analysis, not for quick checks.
What Free Scanners Usually Miss
Secret scanning. Most tools don't look at your JavaScript at all. They check headers, certificates, maybe DNS. But exposed API keys sitting in your bundle? They'll miss it completely. Email authentication. SPF, DKIM, DMARC - these matter a lot now that Gmail and Yahoo require them for bulk senders. Most security scanners don't check DNS records at all. The full picture. You end up running 3-4 different tools to get a complete view. That's why we built an all-in-one.My Workflow
For a quick check: DomainOptic scan, takes 20 seconds, tells me if anything is obviously broken.
For a new client or deep dive: DomainOptic first to get the overview, then Qualys SSL Labs if I need to dig into certificate chain issues.
For header debugging: SecurityHeaders.com is nice because it shows exactly what each header should look like.
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