Website audit tools: what each type checks

SEO tools

They crawl the site the way a search engine bot does, link by link, and flag what gets in the way of indexing: missing or overlong titles, duplicate descriptions, broken links, redirect chains, pages excluded from the index. It is the largest family of tools, and the one that covers the most pages.

Google's Search Console adds what no outside crawler can see: the pages Google actually indexed and the searches that lead to them. Only the site owner can open it. These tools tell you whether a page can be found; they don't tell you whether what it says is accurate. Our guide to SEO audits versus full website audits shows where the line falls.

Speed tools

PageSpeed Insights runs Lighthouse, Google's tool, on one URL, on mobile and on desktop. It gives two kinds of measurement: a lab load, on a simulated device and network, and, when Google has it, the experience of real visitors.

The two can differ widely, and Google's documentation explains why: one fixed device and network on one side, all of your visitors on the other. These tools measure one URL at a time. Our guides to a slow website and to Largest Contentful Paint explain what those numbers mean.

Security scanners

Configuration scanners such as Mozilla's HTTP Observatory read what the server shows to every visitor: HTTP headers, cookies, redirects. They do it in seconds and can tell you what is missing. Our guide to HTTP security headers explains what each one is for.

They read the public configuration; they are not penetration tests and don't try to get in. Nor do they know whether an unprotected cookie carries a login session or a display preference: that takes knowing what the cookie is for.

Accessibility checkers

They flag what a rule can detect on its own: an image without alt text, low contrast, a field without a label, a button without a name. On those points they are fast and consistent.

The W3C says so in its guide to selecting evaluation tools: tools cannot check all accessibility aspects automatically, and human judgment is required. Lighthouse says it in its own way: part of its accessibility criteria are manual checks, which it lists without scoring. Alt text that is present but wrong, or a path that can't be completed with a keyboard, shows up only when someone uses the page. Our guide to the accessibility statement covers what one commits you to.

What common tools don't look at

Some questions belong to none of these families. They take reading the site, then checking it against a rule or against another of its own texts.

• What the page stores before the visitor makes a choice, and whether rejecting is as easy as accepting.
• What the legal notice actually says, not just whether a link points to it.
• Who supplies each layer of the site, and which country's law that provider answers to: the CLOUD Act question.
• What one page promises and another takes back, such as a description that advertises a benefit the terms of sale withdraw.

Our guide to free website audits covers these points in detail, with extracts from a published report.

Cross-check the tools, then review

Two correct tools can give two different numbers. In our sample report on an online store, real visitors see the home page's main content in 1.6 seconds; in the lab, on a phone with a constrained network, it takes more than 26. The report gives both, and traces the gap to its cause: the weight of the carousel images.

Cross-checking also means placing a defect. A defect found on one page may come from a template a hundred other pages share, and then it gets fixed once. A tool that measures one URL can't know that; an audit that scores pages one by one can see it.

Reviewing, finally, means sorting. A tool lists everything its rules detect, all at the same level. A report says what affects your visitors and what can wait. Our guides on how to audit a website and on auditing a competitor's website show this work from two angles, and the one on website audit cost explains what moves the price.

What we find on the sites we audit

These percentages cover about 30 websites we audited between August 14, 2026 and September 24, 2026. Each one counts only the sites where the point could be checked. Many were audited because a defect showed up quickly, so these figures describe our audits, not websites in general.

What this check doesn't tell you

By Quentin Mathis, Z29K · updated September 28, 2026