Search for free SEO tools and you get listicles recommending products that cost $129 a month, with "free trial available" doing a lot of work in the small print.
This list is organised differently — by the problem you actually have. And for every tool it states where the free tier genuinely stops, because that is the thing these articles always omit.
Full disclosure: we build one of the tools mentioned. It is in the section where it belongs, with its limitations stated alongside everything else.
First: the two tools everyone should have
Google Search Console — free, and nothing substitutes for it
This is the only tool that shows what Google actually does with your site: which pages are indexed, which were excluded and why, what queries you appear for, and your real click-through rates.
Every third-party tool estimates. Search Console reports. If you do one thing after reading this, verify your domain there.
Limitation: only works for sites you own and can verify. Useless for auditing a competitor or a prospect.
Google PageSpeed Insights / Lighthouse — free, unlimited
The reference implementation for Core Web Vitals, and it uses real Chrome user data where available. Built into Chrome DevTools as Lighthouse, so it costs nothing and requires no account.
Limitation: one page at a time, performance and basic accessibility only. No security checks, no crawl, no SSL or DNS.
If you need to crawl a whole site
Screaming Frog — free up to 500 URLs
The reference desktop crawler, and for deep configurable work it is still the tool most technical SEOs reach for. Custom extraction with XPath, log file analysis, granular crawl rules.
Where the free tier stops: 500 URLs. A small brochure site never notices; a store with 3,000 products hits it on the first crawl. It is also a desktop application, so you need a machine you can install software on.
siteIQ — free, no URL cap, browser-based
Ours. It crawls the whole site from the browser with nothing to install and no cap on a standard audit, and it covers ground SEO crawlers skip: security headers, SSL expiry, known CVEs in detected libraries, SPF and DMARC records, and WCAG accessibility — in the same report.
Where it stops: no custom XPath extraction, no log file analysis, and no keyword or backlink data. If you need those, you need one of the tools below instead. We wrote a fuller comparison with Screaming Frog that is honest about which to pick.
If your problem is speed
GTmetrix — free with an account
The waterfall chart is the clearest way to see request-by-request what made a page slow, and you can test from a chosen region — which matters enormously if your problem is geographic rather than structural.
Where the free tier stops: limited tests per day, and the more useful locations and device profiles sit behind a paid plan. Our side-by-side comparison covers where each wins.
WebPageTest — free, genuinely deep
The most detailed performance tool available at any price. Multi-location, multi-device, filmstrip view, connection throttling. Steeper learning curve than anything else here, and worth it once speed is definitely your problem.
If your problem is security
SSL Labs — free, unlimited
The definitive TLS configuration test. Grades your certificate chain, protocol support and cipher suites. Nothing else comes close for that specific job.
Limitation: TLS only. Nothing about headers, content or SEO.
Mozilla Observatory — free
Focused security header analysis with clear explanations of what each missing header exposes you to. Pairs naturally with our guide to what each header does.
MXToolbox — free with limits
The standard for email and DNS diagnostics — SPF, DMARC, blacklist checks, MX records. The interface is dated but the data is reliable. See our explainer on SPF, DKIM and DMARC for what the results mean.
If your problem is keywords and competitors
Be realistic about this category. Keyword volumes, difficulty scores and backlink graphs come from proprietary crawl infrastructure that costs millions to run. Free tiers here are trials, and no genuinely free tool will replace them.
Ahrefs Webmaster Tools — free for verified domains
A genuinely generous free tier: site audit and backlink data for domains you can prove you own.
Where it stops: verification required, so you cannot check a competitor or a prospect.
Ubersuggest — a few free searches daily
Reasonable keyword ideas and content suggestions, cheaper than the enterprise suites if you upgrade. The free allowance runs out quickly.
SEMrush free plan — account required
Around ten requests a day, roughly 100 crawled pages a month, one project. A real trial of a serious product rather than a free tool. Our comparison lays out the free-tier limits in detail.
Google Keyword Planner — free with an Ads account
Volumes come straight from Google. It shows broad ranges rather than exact figures unless you are spending on ads, but the data is first-party.
If your problem is accessibility
WAVE and axe DevTools — both free
WAVE overlays issues visually on the page, which makes it easy to explain to a client. axe runs in DevTools and is the engine behind a lot of automated testing.
Worth knowing: automated tools catch roughly a third of WCAG issues. Keyboard navigation and screen reader testing still need a human. Our accessibility checker covers the automated portion alongside the rest of an audit.
A stack that actually works
For a freelancer or small agency, without paying for anything:
- Google Search Console — real index and query data for sites you own. Non-negotiable.
- A whole-site crawler — Screaming Frog under 500 URLs, or siteIQ above it or when you cannot install software.
- PageSpeed Insights for Core Web Vitals, GTmetrix or WebPageTest when you need the waterfall.
- SSL Labs before any launch.
- One paid suite only when a client is specifically paying for keyword and link work.
How to judge any tool on this list
- Does it crawl the whole site or one page? Single-page checks miss the template-level problems that affect hundreds of URLs.
- Does it need domain verification? That decides whether you can use it on a prospect's site.
- Does it explain findings or just list them? An unprioritised list of failed rules is not actionable.
- What does the free tier actually allow? Not what the pricing page implies — what you can do on day one without a card.
No single tool covers everything, and any list claiming one does is selling something. Pick by the problem you have today.
If you are not sure what your problem is yet, start with a broad audit to find out which category it falls into, then bring in the specialist tool for that area. And if you want to know what a health score is actually measuring before you trust one, we published our full scoring methodology.