Cybersecurity BlogFree SSL Labs Alternative: 8 Tools Compared

Yes. Gossling runs in your browser at gossling.checkfix.io, costs nothing, produces an overall grade from A+ to F, and may be used commercially. No download, no account, no shared queue.

For the record: Gossling is our own tool. It exists because a TLS assessment during a customer security check kept failing on us, and none of the available tools would return a result. Three weeks later the scanner was running. What it cannot do is further down.

SSL Labs is the reference test. Everyone understands the grade, and the Qualys SSL Server Rating Guide is the basis almost everyone else builds on, ourselves included. In daily work you still hit three walls.

The licence. Automating the test means using the API, because scraping results from the website is explicitly forbidden in the terms of use. The API in turn is not cleared for commercial purposes without express permission from Qualys. Hosting providers, CAs, CDNs and web development agencies can get relaxed terms, but with conditions attached: the service has to be free for all your customers, and full results may only be passed on as a link to ssllabs.com.

The scope. SSL Labs only tests publicly reachable web servers. Mail servers, non-standard ports and internal systems are out.

The queue. You share it with everyone else and have no idea when your scan runs.

Tool	Form	Overall A–F grade	Cost and limits	Commercial use
Gossling	Online + API, self-hosted optional	yes (A+ to F)	free	permitted
Qualys SSL Labs	Online + API	yes (A+ to F)	free, public web servers only	API by permission only, scraping the site forbidden
testssl.sh	CLI script (download)	yes	free (GPLv2)	permitted
sslyze	CLI (download)	no, checks against Mozilla configuration profiles	free	permitted
sslscan	CLI (download)	no, plain list of findings	free	permitted
ImmuniWeb SSL Security Test	Online + API	yes	10 tests per month without an account, 20 with a free account, then from 25 EUR per month	white-labelling of reports forbidden
Hardenize public report	Online	no, per-check assessment	public report free	product itself sold through Red Sift enterprise sales
Mozilla Observatory (TLS)	retired in 2024	–	–	–

The deepest free TLS tool available, maintained for years, with community experience no young project catches up on. The catch is the form: a bash script whose results depend on your OpenSSL version and your shell. On some targets it simply stops. Excellent for a technician with a terminal, wrong choice for „quickly check the client domain and forward the report”.

Both free, both command line, both give you solid technical detail. What they do not give you is an overall grade. sslyze checks against the Mozilla TLS configuration profiles and tells you pass or fail. That helps with hardening. It does not help when you have to explain to management where the company stands.

Online, graded, with a PDF report and checks against PCI DSS, HIPAA and NIST requirements. The limit is published openly: ten tests per month without an account, twenty with a free account, then from 25 EUR per month for 50 tests. An agency with thirty client domains burns through that in the first month.

Built by Ivan Ristić, the creator of SSL Labs, and the public report is still free to run. It is good, too: DNS, mail servers, SPF, DMARC, certificates and headers in one view. What it does not produce is an overall grade, only an assessment per check. Since the Red Sift acquisition the product behind it has moved into the enterprise segment and the self-service tier is gone.

The old Observatory had a dedicated TLS section. Mozilla shut that platform down in 2024. The new HTTP Observatory on MDN only checks HTTP headers, and according to Mozilla there are no plans to bring TLS and certificate analysis back. Anyone still pointing at an Observatory TLS rating is pointing at nothing.

Gossling is not a script but a Go scanner with a web interface and an API. Point it at a domain, an HTTPS service on any port, or a STARTTLS mail server (smtp://, imap://), and results stream in live.

Among the things it tests:

• Protocols: SSLv2/3, TLS 1.0 to 1.3, downgrade and consistency checks
• Cipher suites: enumeration per version, strength overview, server preference
• Certificates: chain validation, CT/SCT, OCSP stapling, Must-Staple, CAA, revocation
• Trust stores: Mozilla, Apple, Android, Java, Windows
• Vulnerabilities: Heartbleed, POODLE, ROBOT, DROWN, BEAST, CRIME, FREAK, Logjam, Sweet32
• HTTP headers: HSTS including preload eligibility, CSP, cookies

Grading follows the SSL Labs weighting (protocol 30 per cent, key exchange 30 per cent, cipher strength 40 per cent) and adopts the cap logic from testssl.sh. Heartbleed means F. TLS 1.0 still enabled caps the grade at B, no matter how clean the rest of the configuration is. Across multiple endpoints, the worst one counts.

How to run the scan step by step and what the individual values mean is covered in our guide Test SSL/TLS online. What sits behind a warning like „SSL obsolete version” is broken down in this article.

Gossling does not simulate browser and client handshakes the way SSL Labs does. For compatibility questions („will this still work with an older Java client?”) that is a real difference. The active padding oracle tests for Zombie POODLE and Golden DOODLE are deliberately opt-in, because they send additional manipulated handshakes to the server. And testssl.sh has simply seen more years and more edge cases.

Internal systems on a private network are out of reach for the online scanner, as they are for any online tool. If you need to assess staging environments or RFC1918 hosts, you run Gossling in your own network via Docker. SSL Labs does not offer that option at all.

A scanner tells you what is wrong. The more useful question is what to do about it.

Gossling covers TLS/SSL. CheckFix assesses your entire external attack surface in one run: mail security (SPF, DKIM, DMARC), TLS/SSL, known vulnerabilities through CVE correlation, security headers and internet interfaces. The free Security Check gives you the A to F rating across all five categories. With CheckFix you also get the prioritised ToDo CheckList: which finding, which system, how urgent, which action. No raw export that somebody has to interpret first.

SSL Labs remains a good choice for a single public web server. But the Gossling grade rests on the same rating guide, and we verify it continuously against badssl.com and the SSL Labs API itself. The grade you get speaks the language your auditors already use.

The difference sits next to it: mail servers, services on non-standard ports, automation through an API, and anything you do on behalf of a client. That is exactly where we built Gossling.

And after that? If you want to know what the rest of your attack surface looks like, the Security Check is free and takes barely longer than a coffee.