Running a website means keeping a lot of plates spinning. Performance, security, SEO, accessibility, email deliverability — there's always something to check. The good news is there are plenty of free online tools that let you test all of these things in seconds, with no sign-up required for most of them.
Here's a curated collection of the best ones, organised by category.
Performance & Speed
Slow websites lose visitors. These tools analyse your page load times, Core Web Vitals, and give you specific recommendations to speed things up.
Google PageSpeed Insights
URL: pagespeed.web.dev
The go-to tool for most developers. Paste in a URL and get a detailed Lighthouse report covering performance, accessibility, best practices, and SEO. It shows both lab data (simulated) and field data from real Chrome users (CrUX). You get a score out of 100 for each category, plus a prioritised list of opportunities and diagnostics.
What makes it particularly useful is the Core Web Vitals assessment — Largest Contentful Paint (LCP), Cumulative Layout Shift (CLS), and Interaction to Next Paint (INP) — which are the metrics Google uses as ranking signals.
GTmetrix
URL: gtmetrix.com
GTmetrix gives you a detailed performance report with a waterfall chart showing exactly how your page loads. The free tier tests from a single location (Vancouver, Canada) using Chrome on a simulated desktop connection. You get a clear breakdown of performance scores, web vitals, and a visual timeline of the page rendering.
The waterfall view is what sets GTmetrix apart — it makes it easy to spot which specific resources are slow, blocking, or unnecessarily large.
WebPageTest
URL: webpagetest.org
WebPageTest is the most advanced free performance testing tool available. Originally open-sourced in 2008 and now maintained by Catchpoint, it lets you test from multiple global locations, different browsers, various connection speeds, and even real mobile devices. You get filmstrip views, video comparisons, detailed waterfall charts, and connection-level breakdowns (DNS, TCP, TLS timings).
If you want to go deeper than PageSpeed Insights allows, this is the tool. A free account unlocks the full feature set.
SEO
Make sure search engines can find, understand, and properly display your content.
Google Rich Results Test
URL: search.google.com/test/rich-results
If you use structured data (JSON-LD, Microdata, etc.), this tool checks whether your page is eligible for rich results in Google Search — things like star ratings, FAQ accordions, recipe cards, and event listings. Paste in a URL or code snippet and it'll validate your markup and show you exactly which rich result types are supported.
Ahrefs Free SEO Tools
URL: ahrefs.com/free-seo-tools
Ahrefs offers a collection of free tools without needing a paid subscription. Their free Webmaster Tools gives you site audit reports, backlink data, and keyword tracking for sites you own. They also offer standalone free tools for checking backlinks, broken links, and keyword ideas.
Google Search Console
URL: search.google.com/search-console
Not an instant checker like the others, but it's free and essential. Once you verify ownership of your site, Search Console shows you which queries bring traffic, your average position, crawl errors, indexing status, Core Web Vitals from real users, and mobile usability issues. If you only use one SEO tool, it should be this one.
SSL / TLS
HTTPS is non-negotiable in 2026. These tools check that your SSL certificate is valid, properly configured, and using modern protocols.
Qualys SSL Labs Server Test
URL: ssllabs.com/ssltest
The gold standard for SSL testing. It performs a deep analysis of your SSL/TLS configuration and gives you a letter grade (A+ through F). It checks your certificate chain, protocol support, key exchange, cipher strength, and known vulnerabilities like BEAST, POODLE, and Heartbleed. If you're not getting an A or A+, the report tells you exactly what needs fixing.
Hardenize
URL: hardenize.com
Hardenize goes beyond just SSL — it checks your entire domain's security posture including HTTPS configuration, certificate transparency, HSTS, DNS security (DNSSEC), email security (SPF, DKIM, DMARC), and more. The free public report gives you a comprehensive snapshot. Think of it as SSL Labs plus a whole lot more.
Security Headers & Configuration
Your site might be serving content over HTTPS, but are your HTTP security headers properly set?
Security Headers
URL: securityheaders.com
A quick scanner built by Scott Helme (now a Snyk project) that grades your site's HTTP response headers from A+ to F. It checks for the presence and correct configuration of headers like Content-Security-Policy, X-Content-Type-Options, X-Frame-Options, Referrer-Policy, Permissions-Policy, and Strict-Transport-Security. Over 362 million scans have been run on this tool — and the majority of sites still score an F.
Mozilla HTTP Observatory
URL: developer.mozilla.org/en-US/observatory
Developed by Mozilla, the HTTP Observatory performs an in-depth assessment of your site's HTTP headers and security configuration. It has scanned over 6.9 million websites through 47 million scans since launching in 2016. The scoring is strict but fair — it checks Content Security Policy, cookies, CORS, HTTPS redirection, Subresource Integrity, and more. It complements Security Headers nicely as they weight things slightly differently.
Accessibility
Around 16% of the world's population has a disability. Making your website accessible isn't just good practice — in many jurisdictions it's a legal requirement.
WAVE
URL: wave.webaim.org
WAVE is a widely-used web accessibility evaluation tool from WebAIM at Utah State University. Paste in a URL and it overlays icons directly onto your page showing errors, alerts, structural elements, and ARIA usage. It checks against WCAG (Web Content Accessibility Guidelines) and highlights issues like missing alt text, poor contrast, empty links, and missing form labels.
There are also browser extensions for Chrome, Firefox, and Edge if you need to test pages behind a login or on localhost.
Lighthouse Accessibility Audit
This is built into Google PageSpeed Insights (mentioned above) and Chrome DevTools. While it only catches around 30-50% of accessibility issues through automated testing, it's a good starting point and surfaces the most common problems.
HTML & Code Validation
Browsers are forgiving of bad markup, but that doesn't mean your code is correct. Invalid HTML can cause rendering inconsistencies, accessibility problems, and SEO issues.
W3C Markup Validation Service
URL: validator.w3.org
The official HTML validator from the World Wide Web Consortium. Submit a URL, upload a file, or paste in code directly. It checks your HTML against the relevant specification and reports errors and warnings. Modern HTML5 validation is available at validator.w3.org/nu (the Nu Html Checker).
W3C CSS Validation Service
URL: jigsaw.w3.org/css-validator
The companion validator for CSS. Checks your stylesheets against the CSS specification and catches syntax errors, invalid properties, and deprecated features.
Email Deliverability
If your website sends email (contact forms, newsletters, transactional emails), you need to make sure those emails actually arrive in inboxes.
Mail-Tester
URL: mail-tester.com
Brilliantly simple — it gives you a unique email address, you send a test email to it, then check your score out of 10. It analyses your SPF, DKIM, and DMARC records, checks if your sending IP is on any blacklists, evaluates your message content for spamminess, and verifies your reverse DNS. Three free tests per day.
MXToolbox
URL: mxtoolbox.com
A comprehensive suite of email and DNS diagnostic tools. The SuperTool lets you run MX lookups, blacklist checks, SMTP diagnostics, SPF/DKIM/DMARC validation, and much more. If you're debugging email delivery issues, this is where you'll likely end up. The individual tools are free; monitoring and alerts are paid.
DNS
When you change hosting, nameservers, or DNS records, you need to know whether the changes have propagated globally.
whatsmydns.net
URL: whatsmydns.net
A clean, fast DNS propagation checker. Enter a domain, pick a record type (A, CNAME, MX, TXT, etc.), and instantly see the results from DNS servers around the world, displayed on a global map. Ideal for checking whether your DNS changes have propagated after switching hosts or updating records.
DNSChecker
URL: dnschecker.org
Similar to whatsmydns.net but with more than 100 global DNS servers and additional tools. Beyond propagation checking, the site offers a full suite of DNS diagnostics including domain health reports, WHOIS lookups, blacklist checks, port scanning, and SPF/DKIM/DMARC validation.
Technology Stack
Curious what a website is built with? Or want to check what your own site is exposing?
BuiltWith
URL: builtwith.com
Enter any domain and BuiltWith identifies the technologies in use — CMS, hosting provider, analytics tools, JavaScript frameworks, CDN, email services, advertising platforms, and more. The free lookup is surprisingly detailed. It's useful for competitive research, but also for auditing your own site to see what third-party scripts and services are visible to the outside world.
Bonus: All-in-One Checkers
A few tools that cover multiple areas at once:
- web-check.xyz — An open-source all-in-one site analysis tool that checks DNS, SSL, headers, performance, cookies, server info, redirects, and more in a single scan.
- webhint.io — Microsoft's linting tool for the web. Checks accessibility, performance, security, PWA readiness, and cross-browser compatibility.
- yellowlab.tools — Focuses on front-end quality: page weight, requests, DOM complexity, CSS complexity, JavaScript issues, and server configuration.
Making It a Habit
No single tool covers everything, and no tool replaces manual testing and real user feedback. But running your site through a few of these checkers on a regular basis — especially after making changes — is one of the easiest ways to catch problems early.
A good routine might look like:
- Monthly: PageSpeed Insights + Security Headers + SSL Labs
- After DNS changes: whatsmydns.net or DNSChecker
- After design changes: WAVE accessibility check
- After email config changes: Mail-Tester + MXToolbox
- Quarterly: Full sweep with Mozilla Observatory + W3C Validator
Bookmark the ones that matter most for your site and make them part of your workflow. They're free, they're fast, and they'll save you from a lot of preventable headaches.
