SEO audit tools: what each kind actually checks

A complete SEO audit runs on three tools, and two of them are free. Use a site crawler to see your pages the way a bot does, Google Search Console to see what Google actually did with them, and PageSpeed Insights for speed and layout. Four different kinds of product are sold as SEO audit tools, they check different layers, and once you know which layer each one owns you can assemble a full audit in an afternoon.

That matters because people buying an audit tool are answering one of two questions. Either something has gone wrong and they want to find it, or nothing has gone wrong and they want to know what to improve next. Pick the tool by which question you are asking, and read the findings rather than the score out of a hundred.

The four kinds of tool

Site crawlers. These fetch your pages one by one, follow the links, and report what a bot sees. Screaming Frog SEO Spider and Sitebulb are the common desktop options, with Lumar, OnCrawl and JetOctopus used on large sites. A crawler is the only tool that gives you the real structure of your site: every redirect chain, every broken link, every page with no internal links pointing at it, every duplicate title. Screaming Frog is free up to 500 URLs per crawl, which covers a small site completely.

Platform suites with an audit module. Ahrefs Site Audit, Semrush Site Audit and Moz Pro run a cloud crawl on a schedule and present the findings as a prioritised list with a score. Their real advantage is not the crawl. It is that they sit next to their own keyword and backlink indexes, so a technical finding sits beside the traffic and links it affects.

Google's own free tools. These report what Google did rather than what it should have done, which makes them the reference the others get checked against. Search Console shows which pages are indexed, which were excluded and why, your actual queries, and your Core Web Vitals from real visits. PageSpeed Insights and Lighthouse measure performance. The URL Inspection tool shows the rendered page Google holds. Set these up first, because they cost nothing and they settle arguments.

Single purpose checkers. A structured data validator, a robots.txt tester, an hreflang checker, a mobile rendering check. Reach for these once a crawl has told you where to look, and they will give you a precise answer fast.

There is a fifth category worth naming plainly: the free "enter your URL for an instant SEO score" page. Those run a handful of checks on one URL and collect your email address. Use one as a prompt to look properly, then do the real audit with the three tools above.

Kind of tool	What it sees	Pair it with
Site crawler	Your real site structure, every page, every link and redirect	Search Console, for what Google indexed
Suite audit module	Technical findings next to keyword and backlink data	Search Console, for Google's indexing decisions
Search Console	Indexing status and reasons, real queries, real speed data	A crawler, for pages Google never discovered
Single purpose checker	One thing, precisely	A crawl, to tell you where to point it
Instant score page	A few checks on one URL	The afternoon method further down this page

What a complete audit actually covers

Six layers. Check each report against this list, and cover any layer it skips with the tool that owns it.

Crawling and indexing. Can a bot reach every page that should be reachable? Is anything important blocked in robots.txt or carrying a noindex tag? Are canonical tags pointing where you think? Is the sitemap current and does it contain only indexable URLs? This layer first, always, because nothing below it matters if a page cannot be indexed.

Architecture and internal links. How many clicks from the home page to your money pages? Which pages have no internal links at all? Which pages are competing with each other for the same query? Internal linking is the most under used lever on most sites and crawlers find the problems in minutes.

Content and coverage. Does a page exist for each question your buyers actually ask, and does each page answer one question rather than six loosely? Thin and duplicated pages belong here too. This layer is judged by reading, so put a person on it and give them the crawl's title and word count export to work from.

On page and markup. Titles, headings, descriptions, image alt text, structured data. For structured data, check it against the types Google lists in its search gallery, because a validator will happily approve markup that produces nothing in search.

Performance. Google's published thresholds for the Core Web Vitals, measured at the 75th percentile of real page loads, are 2.5 seconds or less for Largest Contentful Paint, 200 milliseconds or less for Interaction to Next Paint, and 0.1 or less for Cumulative Layout Shift. Use the field data in Search Console for the verdict and Lighthouse to find the cause.

Off site and measurement. Your backlink profile, your presence on the directories and listing sites in your category, and whether your analytics actually records what you think it does. Broken conversion tracking is more common than any technical SEO fault.

How to read the score and the issue list

Each vendor weights its score differently, so use the score for the one job it does well: tracking your own direction on the same tool over time. Two vendors will disagree on the number, and both can be right about their own scale.

Audit tools count issues, so do the weighing yourself. A thousand missing alt attributes on decorative images will fill a report while one wrongly applied noindex tag on a category page sits lower down. Re-sort every report by what happens if you ignore the finding, and work from the top of your own list.

How to audit a site in an afternoon

• Crawl the site. Export the redirect chains, the 404s, the pages with no inbound internal links, and the duplicate titles.
• Open the Search Console page indexing report. Read the excluded reasons. Anything commercially important in that list is your first job.
• Compare the two lists. Pages a crawler can reach but Google excluded are where the real problems are.
• Check your robots.txt and your sitemap by hand. They take two minutes and cause the largest failures.
• Run your five most important pages through PageSpeed Insights and read the field data, not the lab score.
• Read your three most important pages as a buyer would. Decide whether the first paragraph answers the question the page is named after.

What this page covers, and what it leaves out

This page covers what each kind of audit tool checks, the six layers a full audit has to reach, and how to run one in an afternoon. For a feature by feature comparison and current prices, go to the vendors directly, since both move. For link building and local listings, use a separate guide.

What people ask about SEO audit tools

Is a free SEO audit tool enough?

For a small site, yes, for nearly everything that matters. Search Console plus a free crawl of up to 500 URLs plus PageSpeed Insights covers the same ground as a paid report. Pay when you need scheduling, history, large crawls, or keyword and backlink data in the same screen.

What does a person add that a tool does not?

Judgement is the part a person brings. Read the audit, then go and look at your pricing page, your overlapping pages and your weakest opening paragraphs, because that is where the wins are. Those findings usually outrank everything in the technical list.

How often should I run an audit?

Run a full audit whenever something changes materially: a migration, a redesign, a platform change, or a traffic drop. Schedule a crawl monthly to catch regressions, and check Search Console weekly so you are always working from current data.

Why do two tools report different numbers of issues?

Crawl settings, JavaScript rendering, parameter handling and each vendor's definition of an issue all differ. Pick one tool as your reference, track it over time, and judge progress on that single scale.

Do I have to fix everything the report lists?

Work in this order and you will capture nearly all the value: anything that stops a page being indexed, anything that breaks a page for a visitor, then anything on a page that makes money. Everything after that is housekeeping you can schedule.

One layer worth adding to your audit

Every audit tool in this guide reads your site: crawl, speed, markup, links. None of them reads the answer a buyer gets when they skip the results page and ask an assistant which provider to trust. That answer is assembled from sources you may never have audited, such as review sites, directories and other people's comparison pages.

Add one row to the audit. Take five questions a customer would ask, put each to ChatGPT, Gemini and Perplexity, and write down who is named and which pages are cited. AI Knows Us runs that exercise at a scale a spreadsheet will not, and the sources it lists are your next audit targets.