SEO audit tools fall into three groups, and the difference between them decides how you have to read a number. First, the first-party tools: Google Search Console and Bing Webmaster Tools show what the search engine itself recorded about your website, meaning clicks, impressions, and indexing status, free of charge once you verify ownership. Second, the crawlers: Screaming Frog, Lighthouse, PageSpeed Insights, and linkinator fetch your pages themselves and measure what they find. Third, the third-party index suites such as Ahrefs, Semrush, and Sistrix, which estimate search volume, visibility, and authority scores from their own data set. Group one is the authoritative source for your own site's search performance, group two measures the live object, group three extrapolates. A basic audit costs you nothing: Search Console, Bing Webmaster Tools, Lighthouse, PageSpeed Insights, free Screaming Frog, and linkinator carry a small website. Whether you pay beyond that depends on two axes: the number of your URLs and the feature you need. JavaScript rendering in the crawl, saved and comparable crawls, and data about other people's websites are not available for free.
I run my business as a solo freelancer with a workforce of AI employees, and measuring my own website is a standing role there, not a subscription. The concept is on AI employees, the process of an audit in How to Run an SEO Audit With AI. This piece covers the other half: what each tool really does, and when paying for one earns its money.
The three kinds of SEO audit tools
Most tool lists sort by price and throw the three groups together. That misleads: two tools with the same price tag can deliver very different qualities of truth. All three measure something, but not the same thing. The search engine tools report what the search engine itself recorded, and say nothing about other people's websites. A crawler measures your server's answer at the moment of the fetch, never how often somebody searches for it. A suite extrapolates from an incomplete data set, but does see domains you do not own. Cash book, sample, market research: all three have their place, but only the first tells you what actually happened in search.
The comparison by criteria that carry a decision
All prices and limits as of September 2026: Screaming Frog and Moz rechecked on 20 September 2026, the rest retrieved on 19 September 2026.
Look at the last column at the top: the two tools with the best data quality in the field have no paid tier, because they are not a product but the search engine's feedback channel to the site owner.
Search Console and Bing Webmaster Tools: the search engine's first-party data
Google describes Search Console as a tool that helps "anyone with a website to understand how they are performing on Google Search". Once you verify ownership you get clicks, impressions, CTR, and average position per query and per page, plus the reasons a page is not in the index. Performance data reaches back 16 months and then disappears, so export it regularly. The interface serves 1,000 rows per report: if you want to analyse more, you need the API or the export, not a more expensive subscription.
Since 3 June 2026 there is an additional report on generative AI search, available worldwide since 31 August 2026. It shows impressions in AI Overviews and AI Mode by page, country, device, and date, but explicitly no clicks, no CTR, and no queries. That is the yardstick when someone sells you a tool that promises exactly those numbers for AI search.
Bing Webmaster Tools is free as well and matters more for AI search than Bing's market share suggests. "Search Performance" shows clicks and impressions per page and per keyword, and since 10 February 2026 "AI Performance" comes on top: "Total Citations", "Average Cited Pages", and "Grounding Queries", meaning how often, across how many pages, and with which phrasings the AI pulled in your content as a source. Microsoft recommends running both tools side by side, because Bing pools web search as well as chat and Copilot answers. The Bing view only reaches back six months instead of Google's 16: there you start exporting earlier.
Crawlers: what your own fetch tells you
A crawler does not replace search engine data. It answers a different question: what does a visitor or a bot find when it requests your page?
Screaming Frog crawls up to 500 URLs per run for free, and that is only the best known of its limits. The vendor's pricing page puts both editions side by side, line by line: broken links and redirects, page titles and metadata, meta robots, hreflang, exact duplicates, XML sitemaps, and the visualisations are included for free. Not included are, among others, JavaScript rendering, saving and reopening crawls, the crawl configuration, scheduling, crawl comparison, structured data validation, custom source code search and extraction, and the integrations with Google Analytics, Search Console, and PageSpeed Insights (pricing page retrieved on 20 September 2026). For the basic audit of a small website that ships finished HTML, that is enough. As soon as content is loaded via JavaScript, or you want to compare two crawls and repeat a measurement on a schedule, the licence at 245 euros a year stops being a question of size and becomes a question of features.
Lighthouse is open source and audits a single page across several categories, performance and SEO among them. PageSpeed Insights combines that lab measurement with field data from the Chrome UX Report, which according to Google only contains pages with "a large enough number of visitors in order to create a statistically significant dataset". For a young website that means lab data instead of field data, and the two belong in separate columns. Anyone who still shows you real-user values in that situation has estimated.
linkinator and curl round it off: broken links, redirect chains, robots.txt and sitemap checked against each other, no interface, no limit, no subscription.
Third-party suites: what they are good for and what not
Ahrefs, Semrush, and Sistrix run their own crawler and data set. That produces the real value of this category: competitor backlink profiles, their rankings, and their development over years. There is no free equivalent for that, and anyone fighting for contested search terms is right to buy it.
What they do not deliver is precision about your own site. Search volume is an extrapolation, even in the original: Google writes about its own Keyword Planner that "Your search volume statistics are rounded". The same blur sits in every volume figure built on top of it. Autocomplete suggestions, too, only prove that a phrasing gets typed, not how often and not by whom: of ten suggestions for "seo audit tool", three were recognisably exam questions from a learning platform.
The second figure that calls for caution is authority scores: Domain Authority at Moz, Domain Rating at Ahrefs, Authority Score at Semrush. Those are vendor metrics, not Google values, and Moz says so on its own explainer page: "Domain Authority is not a Google ranking factor and has no effect on the SERPs" (page last updated 18 March 2025, retrieved on 20 September 2026). Google's John Mueller said the same in 2020: "Just to be clear, Google doesn't use Domain Authority at all when it comes to Search crawling, indexing, or ranking." As a rough comparison between two domains inside the same tool these scores work. As a target in an action plan they do not.
The free tiers do not help much here: Ahrefs Webmaster Tools only covers verified sites you own, the Semrush free access is "1 demo project" and "10 reports per day across all vital tools" according to the vendor, and Sistrix has no free tier at all. So you do not assess other people's domains for free.
When a paid tool pays off
Two axes decide, not one: the size of the website and the feature you need.
- Up to roughly 500 URLs, finished HTML: the six free tools in the table carry the basic audit. A paid suite rarely answers a question here that you had not already answered.
- Beyond 500 URLs: the crawl stops. A Screaming Frog licence costs 245 euros a year and lifts exactly that limit.
- As soon as a feature is missing: JavaScript rendering for a page that loads its content dynamically, saved crawls for the before-and-after comparison, custom extractions, scheduling. That can happen at eighty URLs, and then the feature decides, not the size.
- As soon as you have to assess other domains: competitor backlinks, other people's rankings, market trends. No free route leads there, and that is the reason to buy Ahrefs, Semrush, or Sistrix. For the German market Sistrix is worth a look, for international backlink depth Ahrefs.
If you only need the occasional ranking sample, SerpAPI or DataForSEO come cheaper than a subscription: you pay per query, not per month.
What AI adds and what it does not
"AI SEO audit tool" has become a search term of its own. AI changes nothing about the grouping above, it only shifts who reads the output. A language model without connected tools has no crawler and no way into your Search Console; ask it for your Core Web Vitals anyway and you get an invented number. An agent with tool access starts Lighthouse or the API call itself and delivers real values. The rule that holds the difference: every figure in the report points at a saved file, otherwise it comes out.
The employee who works this toolbox
The bottleneck on small websites is almost never the missing tool, it is that nobody runs the measurement regularly and keeps the results. That is exactly why this is a role here and not a project.
Sebastian, my AI employee for SEO and GEO, works with the box from this piece, free tier as the default: Lighthouse, Unlighthouse, linkinator, Playwright, and the PageSpeed Insights data run without approval, he reads Search Console and Bing Webmaster Tools once access is in place, and paid tools only after an explicit decision from me. Every raw output lands in a dated job folder, every finding names its source. He changes nothing on a live website and submits nothing in someone else's account. He measures, I decide.
Why Bing sits next to Google as an equal here comes from a finding on my own website: the page with the most Google clicks and the one with the most Copilot citations were not the same page. Measure only one and you see half. How the roles are split here is in My AI Workforce; if you are still working out where AI pays off in your business, start with Bringing AI to a Small Business.
Frequently asked questions
What is an SEO audit, exactly?
A stock-take of your website in four areas: technical setup, on-page work, structured data, and, for a local business, local relevance. The result is a list of findings, each with its source, plus a prioritised action plan. An audit tells you where you stand, not where you will stand afterwards.
What is the best free SEO audit tool?
There is no single one, because these tools measure different things. Search Console, Bing Webmaster Tools, Lighthouse, and free Screaming Frog together cover the basic audit of a website under 500 URLs. Not covered: JavaScript rendering in the crawl, saved crawl comparisons, data about other people's domains.
Is there an SEO audit tool from Google?
Three of them: Search Console for clicks, impressions, and indexing, PageSpeed Insights for load times with lab and field data, Lighthouse as an open-source audit of individual pages. All three free. A single overall "SEO score" is not among them, and that is correct.
Does an AI SEO tool beat the free tools?
For assessment yes, for measurement it depends on the connection. Without connected tools a language model collects no measurement itself; with tool access an agent starts the crawl or the API call. The sequence stays the same: measure, save the output, have the output assessed.
Are Domain Authority and visibility indexes reliable numbers?
They are reliable metrics of the respective vendor, but not Google values: Moz itself writes that Domain Authority is not a Google ranking factor and has no effect on the search results. Usable as a rough comparison of two domains inside the same tool, not as a target in an action plan.
Where to go from here
Start on the first-party side, because it is the foundation and costs nothing: set up Search Console, put Bing Webmaster Tools next to it, verify ownership on both. Then one Lighthouse run over your most important page and one Screaming Frog crawl over the domain. After those four steps you have, under 500 URLs, the basic audit in hand and you can see which feature you are still missing. Usually none; what is missing more often is the order in which a small business approaches SEO.
If you do not want to run this every quarter yourself, the role is more interesting than the tool: how to build one is in Creating an AI Employee: How to Start. The templates and the tool checklist are in my community: if you get stuck on your first crawl, ask there or bring it to the call.
