Nessus and SiteSecurityScore solve different problems
Nessus by Tenable is a paid, plugin-based vulnerability scanner for network and host infrastructure. Its plugin library covers CVEs across operating systems, network devices, and services, and it supports credentialed host scanning, internal infrastructure assessment, and compliance auditing. It is designed to find missing patches and known vulnerabilities across servers and networks. It is not built for web application security headers or response configuration.
That work happens at the network and host layer. The web configuration layer is a separate concern. A server can pass a network scan and still ship pages with no Content Security Policy, a missing HSTS header, cookies without Secure or HttpOnly flags, weak TLS settings, or absent DNS email authentication records. SiteSecurityScore is purpose built for that web response posture, the configuration layer attackers probe first. It grades all of these areas in a single free scan with no setup and no agents, so the two tools complement each other and you cover the web layer you should not skip.
Nessus vs SiteSecurityScore: side by side feature comparison
Web Security Headers
| Feature | SiteSecurityScore | Nessus |
|---|---|---|
| Content Security Policy (CSP) | Expert tier | |
| Strict Transport Security (HSTS) | Expert tier | |
| X-Frame-Options | Expert tier | |
| X-Content-Type-Options | Expert tier | |
| Referrer-Policy | ||
| Permissions-Policy, COOP, COEP, CORP |
Web Configuration Layer
| Feature | SiteSecurityScore | Nessus |
|---|---|---|
| Deep CSP directive breakdown | ||
| DNS security (SPF, DKIM, DMARC, CAA) | ||
| Cookie security attributes | ||
| CORS header analysis | ||
| security.txt validation | ||
| Mixed content and information disclosure |
Features
| Feature | SiteSecurityScore | Nessus |
|---|---|---|
| Free scan, no account for basics | ||
| Letter grade scoring | ||
| Actionable fix recommendations | ||
| PDF report generation | ||
| REST API for automation | ||
| Browser extension (authenticated pages) | ||
| Daily monitoring with email alerts | ||
| CSP violation and NEL reporting | ||
| MCP connector for Claude Code and Codex | ||
| Free header generator tools |
Network & Host Vulnerabilities
| Feature | SiteSecurityScore | Nessus |
|---|---|---|
| Plugin-based CVE detection | ||
| Operating system vulnerability checks | ||
| Credentialed host scanning | ||
| Network device and service scanning | ||
| Compliance and audit policy templates | ||
| Internal infrastructure assessment |
Nessus offers dynamic web application scanning in its higher Nessus Expert tier, which requires Docker and limits the number of web application URLs you can scan per period. SiteSecurityScore delivers instant, unlimited web header and deep CSP posture checks with a letter grade and copy and paste fixes, free and with no setup.
What Nessus scans vs the web configuration layer
The cleanest way to think about it is by layer. Nessus owns the network and host side. SiteSecurityScore owns the web response side and gives you everything you need for the web configuration layer in one scan. Here is the coverage a network and host scanner is not designed to focus on.
Security headers analysis
CSP, HSTS, X-Frame-Options, X-Content-Type-Options, Referrer-Policy, Permissions-Policy, COOP, COEP, and CORP. These headers prevent XSS, clickjacking, and data leakage at the browser level.
Deep CSP analysis
Directive by directive breakdown of your Content Security Policy. It flags unsafe-inline, overly broad wildcards, and missing directives, then helps you tighten the policy.
DNS security records
SPF, DKIM, DMARC, and CAA record analysis. Find gaps in email authentication before attackers exploit them for phishing and spoofing.
Cookie security audit
HttpOnly, Secure, SameSite, Path, Domain, and prefix checks for every cookie. Spot session hijacking and CSRF risks at a glance.
CORS and security.txt
Reviews Access-Control-Allow-Origin and credentials settings for permissive cross-origin rules, and verifies your security.txt disclosure channel.
Mixed content and disclosure
Detects insecure mixed content and information disclosure such as server banners and verbose error responses that leak details about your stack.
Continuous web security monitoring with email alerts
Infrastructure scans tend to run on a schedule you manage. Your web headers and CSP can drift between those runs. A deploy ships a header change or a third party script breaks your policy, and you will not know until the next manual scan.
SiteSecurityScore gives you free continuous daily monitoring that checks your HTTP security headers, Content Security Policy, TLS configuration, DNS records, and cookie security in a single pass with no setup and no agents. When anything changes, you receive an email alert immediately. It also collects CSP violation and Network Error Logging reports so you can see real browser-side problems as they happen.
Automated daily scans
Every monitored site is scanned once per day covering headers, CSP, TLS, DNS, and cookies.
Email alerts on changes
Get notified when your security posture changes, a certificate nears expiration, or a header is removed.
Free security header generator tools
Knowing which headers are missing is only half the job. You also need correct values. SiteSecurityScore gives you free generator tools that produce copy and paste configurations for your web server in seconds.
Scan authenticated pages a public scan cannot reach
Chrome Extension
Public scanners can only reach pages you can open without logging in. The SiteSecurityScore browser extension captures real response headers from your authenticated sessions, so you can grade admin panels, internal dashboards, and staging environments with one click. There is also an MCP connector to run scans from Claude Code or ChatGPT Codex.
Run a free website security scan
Enter any URL and get a complete web security audit covering HTTP headers, CSP, HSTS, TLS certificates, DNS records, and cookie security. No account required.
Start scanningFrequently asked questions
Is SiteSecurityScore a replacement for Nessus?
SiteSecurityScore and Nessus operate at different layers. Nessus by Tenable is a paid, plugin-based network and host vulnerability scanner that finds CVEs and misconfigurations across servers, operating systems, and devices. It does not focus on web application security headers or response configuration. SiteSecurityScore is the fastest way to grade and fix your web security posture. It is free and instant with no account and no setup, and it is purpose built for the web configuration layer attackers probe first. One scan grades your HTTP security headers, deep CSP analysis, TLS, DNS, cookies, CORS, and security.txt, then hands you copy and paste fixes in seconds. Teams that run Nessus on their infrastructure rely on SiteSecurityScore for the web layer they should not skip.
Does Nessus do web application scanning?
Nessus is built for network and host vulnerability assessment. Dynamic web application and API scanning is available only in the higher Nessus Expert tier, which requires Docker and limits you to a small number of web application URLs per scanning period. It does not target HTTP security headers or CSP posture. SiteSecurityScore owns that layer with everything you need for the web configuration layer in one scan. It delivers instant header and deep CSP analysis across as many sites as you want, with free continuous daily monitoring and email alerts so your posture never drifts unnoticed.
What does SiteSecurityScore check that Nessus does not focus on?
SiteSecurityScore gives you the complete web response posture in one pass. It checks Content Security Policy, HSTS, X-Frame-Options, X-Content-Type-Options, Referrer-Policy, Permissions-Policy, COOP, COEP, and CORP headers, deep CSP directive analysis, TLS and certificate checks, DNS email authentication (SPF, DKIM, DMARC, CAA), cookie security attributes, CORS configuration, security.txt, information disclosure, and mixed content. You get a clear letter grade with copy and paste fixes in seconds, plus free continuous daily monitoring with email alerts and CSP violation reporting, a REST API, a Chrome extension for authenticated pages, free header generator tools, and an MCP connector for Claude Code and ChatGPT Codex. Nessus is oriented toward host and network CVE coverage rather than this header and CSP layer.
Can I monitor my security headers and TLS automatically with SiteSecurityScore?
Yes, and it is free. SiteSecurityScore runs automated daily scans that check your HTTP security headers, Content Security Policy, TLS configuration, DNS records, and cookies in one pass with no setup and no agents. You get an email alert the moment something changes, such as an expiring certificate, a removed header, or a CSP policy edit. It also collects CSP violation and Network Error Logging reports so you can see real browser-side issues as they happen.
Is SiteSecurityScore free to use as a Nessus alternative for web checks?
Yes. SiteSecurityScore gives you free website security scans covering HTTP security headers, TLS certificates, DNS records, Content Security Policy, and cookie security with no account required and free continuous daily monitoring with email alerts. You also get free header generator tools and an MCP connector for Claude Code and ChatGPT Codex. Paid plans add PDF reports, expanded API access, and higher scan limits. Nessus is a paid commercial product, so SiteSecurityScore is the essential way to grade and fix the web configuration layer at no cost.
Can SiteSecurityScore scan pages behind a login?
Yes. SiteSecurityScore ships a Chrome browser extension that captures real HTTP response headers from your authenticated sessions, so you can grade admin panels, internal dashboards, and staging environments for header and CSP issues with one click. There is also an MCP connector so you can run scans directly from Claude Code or ChatGPT Codex.