The Five Tools at a Glance
The differences that matter most aren't feature counts — they're the three constraints below. Whether you need to own the site, whether the tool runs a live crawl on demand, and where the free tier stops.
| Tool | Free limit | Needs site ownership? | Live crawl? | AI / GEO checks |
|---|---|---|---|---|
| SearchVitals | Instant audit on any URL | No | Yes | ✓ Core feature |
| Screaming Frog | 500 URLs per crawl | No | Yes — desktop app | ✗ |
| Semrush Site Audit | 100 pages per audit | No | Yes | ✗ |
| Ahrefs Webmaster Tools | 5,000 crawl credits / project / month | Yes — verification required | Yes | ✗ |
| Google Search Console | Unlimited, but no crawl of your choosing | Yes — verification required | No — reports Google's own index | ✗ |
What "Free" Actually Means Here
"Free SEO audit tool" covers three quite different arrangements, and conflating them is how people end up with the wrong tool:
- Free for any URL. Point it at a competitor, a prospect, or a client site you haven't been given access to yet. SearchVitals, Screaming Frog and Semrush's free Site Audit all work this way.
- Free for sites you own. Ahrefs Webmaster Tools and Google Search Console both require you to prove ownership via DNS record, HTML file or tag. Generous limits, but useless for competitive research or for a prospect who hasn't signed yet.
- Free tier of a paid platform. Semrush's free account is a sample of a $139/month product. The 100-page cap is not a technical limit — it's a trial boundary.
SearchVitals — Free Audit
Cloud-based, no install, and no ownership verification for the free scan. Enter a URL and you get a technical health score alongside an AI Readiness score covering AI crawler access, llms.txt, and citation-ready structured data.
Best for: a fast first read on any site, and the only free option in this list that scores GEO/AI visibility at all.
Where it stops: it's not a 500,000-URL data-extraction crawler. If your job is exporting every H1 on a large e-commerce catalogue to a spreadsheet, this is the wrong shape of tool. Paid plans start at $29/month for continuous monitoring and scheduled crawls.
Screaming Frog SEO Spider — Free Version
A desktop crawler that has been the technical SEO standard since 2010. The free version caps crawls at 500 URLs; the paid licence is £199/year and lifts that to unlimited, bounded only by your machine's memory.
Best for: depth. Redirect chains, duplicate titles, broken links, and — on the paid licence — XPath custom extraction that nothing else on this list matches.
Where it stops: 500 URLs runs out fast on any real site. It runs on your laptop, so crawls are as fast as your connection and reports are files rather than links you can send a client. And it does not evaluate AI crawler access. We cover the trade-offs in depth in SearchVitals vs Screaming Frog.
Semrush Site Audit — Free Account
A free Semrush account includes Site Audit limited to 100 crawled pages. Within that ceiling the issue detection is strong and well explained, with clear severity grouping.
Best for: sampling the quality of a full SEO platform, or auditing a small brochure site that genuinely fits in 100 pages.
Where it stops: 100 pages is the tightest cap here. Semrush is also a full marketing platform — keyword research, backlinks, competitor intelligence — so the entry paid plan is $139/month, which is a lot if auditing is all you needed. See SearchVitals vs Semrush Site Audit for the full breakdown.
Ahrefs Webmaster Tools
The most generous free crawl allowance in this comparison: 5,000 crawl credits per verified project per month, plus backlink and organic keyword data for sites you own. Credits are only consumed by successful HTML page crawls, so redirects and broken links don't eat into the allowance.
Best for: ongoing technical monitoring of your own sites, especially when you also want backlink data in the same place.
Where it stops: verification is mandatory. You cannot audit a competitor, a prospect, or a client site before you have access — which rules it out for the pitch stage of agency work. No AI crawler or GEO checks.
Google Search Console
The odd one out, and the one nobody should skip. GSC is not a crawler you point at a site — it's Google reporting back what its own crawler found on a property you've verified. Index coverage, actual impressions and clicks, Core Web Vitals field data from real visitors, manual actions.
Best for: ground truth. No third-party tool can tell you what Google has actually indexed or which queries you already rank for. It's free and unlimited.
Where it stops: it's diagnostic reporting, not an on-demand audit. It won't tell you a page is slow before Google has enough field data, it can't audit a site you don't own, and it says nothing about non-Google crawlers. Use it alongside a crawler, never instead of one.
The Gap Every Traditional Tool Leaves
All four of the established tools above were designed around one model of search: a crawler fetches HTML, an index stores it, a ranking algorithm orders it. None of them answer the question a growing share of traffic now depends on — can AI answer engines read and cite this page?
That question breaks into checks no traditional audit performs:
- Whether GPTBot, ClaudeBot, PerplexityBot and Google-Extended are allowed through robots.txt and at the CDN. Check yours free.
- Whether your pages render their content without JavaScript, since most AI crawlers don't execute it. See what they receive.
- Whether an
/llms.txtfile tells AI systems what your site covers. Generate one. - Whether your structured data is shaped for citation rather than just rich results. Score your markup.
A site can pass a clean Screaming Frog crawl and a green Search Console report while every AI crawler is being turned away at robots.txt — usually by a rule inherited from a template that nobody revisited. Our complete guide to generative engine optimization covers how to audit for this properly.
Which Free Tool for Which Job
- check_circlePitching a prospect: SearchVitals
- check_circleCompetitor teardown: SearchVitals or Screaming Frog
- check_circleSmall site, deep issue list: Semrush free tier
- check_circleAI visibility check: SearchVitals
- check_circleWhat Google indexed: Search Console
- check_circleMonthly technical sweep: Ahrefs Webmaster Tools
- check_circleOne-off deep crawl: Screaming Frog
- check_circleContinuous monitoring: SearchVitals paid
The pragmatic setup for most people is two tools: Google Search Console for what Google sees, plus one crawler that can be pointed at any URL. The crawler is where the real choice is, and it comes down to whether AI visibility matters to you.