What this audit can't tell you
Every free audit tool has a boundary. Most don't publish theirs, and some report numbers they're actually estimating. Here's exactly where this one stops, and what to use instead.
Why there's a boundary at all
The audit works by fetching your pages and reading the HTML that comes back. That's the same raw material a search engine starts with, so it covers a lot. But some things simply aren't in the HTML: how fast the page loads on a real phone, who links to you, where you rank, how many people search for a term.
Those need a browser running your page, or a crawl of the whole web, or Google's own data. None of that is available from a page fetch. The audit says so instead of filling the gap with a plausible-looking number.
The five things it can't measure
Page speed and Core Web Vitals
It can spot things that usually hurt speed — enormous uncompressed images, a pile of render-blocking scripts, missing width and height on images. It cannot give you an LCP, INP or CLS number, because those need the page actually running in a browser with real user data behind it.
Use instead: pagespeed.web.dev, free, no account needed. Paste your URL and you get both lab scores and, if you have enough traffic, real-world field data.
Backlinks and domain authority
It can see the links going out from your pages. It has no way to see the links coming in, which requires an index of the whole web. Any free tool quoting you a domain authority score is either using a third-party index or making it up.
Use instead: Google Search Console has a Links report for your own site, free. Ahrefs and Semrush have limited free tiers for competitor data.
Your actual rankings
It cannot tell you what position you hold for a term. Search results are personalised, localised and constantly moving, so a single check wouldn't mean much even if it could.
Use instead: Search Console's Performance report gives you real average positions, impressions and clicks per query. This is the only ranking data that's genuinely yours.
Keyword search volume
It can tell you what your pages appear to be about and where the topic gaps are. It cannot tell you how many people search for a phrase each month.
Use instead: Google Keyword Planner, free with a Google Ads account. Search Console also shows the queries already bringing you impressions, which is often more useful.
Pages that render with JavaScript
If your site builds its content in the browser rather than sending it in the HTML, the audit sees an empty shell. This affects some React, Vue and Angular sites — though not those using server rendering or static generation, which most modern frameworks default to.
What it does: detects this and tells you plainly, rather than reporting your page as having no content. If you see that message, it's worth knowing that search engines have their own difficulties with these pages, so it's a finding in itself.
What it covers well
For balance, the flip side. These are the areas where reading the HTML gives you a genuinely complete picture, and where most sites have real problems waiting.
Everything in your page source
Titles, descriptions, headings, canonicals, robots directives, structured data, social tags, alt text, internal links and anchor text. All of it is in the HTML and all of it gets checked across every page fetched.
Content judgement
Whether a page answers its question, whether the answer is near the top, whether the copy says anything a competitor couldn't also say. This is the part traditional crawlers are worst at and a language model is genuinely good at.
Writing the correction
A crawler can tell you a title is too long. It can't write you a better one that fits the character limit, reads well and matches what the page is actually about.
Explaining it in plain terms
No jargon dump. Each problem comes with one sentence on why it costs you something, and an honest estimate of the effort to fix.
A sensible order to work in
If you want a complete picture of a site and you're paying for nothing, this sequence covers almost everything:
- Run this audit for structure, content, markup and the fixes.
- Run your slowest page through pagespeed.web.dev for speed.
- Open Search Console for real queries, positions and indexing problems. If you haven't set it up, do that first — it's the single most valuable free thing in SEO.
- Come back with what you found. Paste the Search Console numbers into the same conversation and Claude can work with them.
That last step is worth knowing about. The audit can't reach Google's data by itself, but it can read a screenshot or an export you paste in. That closes most of the gap without any setup.