SEO check glossary: what each finding means.
Every finding in the free SEO audit links to a one-page explainer: what it is, why it matters and how to fix it, with the official source.
How to use this glossary
Each entry below matches a check in the free audit. When a finding appears in your report, its title links here. The short line under each title tells you the fix, and the detail page adds the reason it matters and the official sources. Start with checks marked Failed in your report, since those carry the most weight in your scores.
The checks are grouped in the report into five areas: Common SEO, Speed, Server and security, Mobile and Advanced SEO. The glossary is a single alphabetical-style list so you can scan for a term you have seen elsewhere, such as canonical, hreflang, HSTS or soft 404. If you do not recognise a term, open its page for a plain-words definition.
A few terms in plain words
Canonical is the one address you want search engines to treat as the main version of a page. Indexing means a search engine has stored a page so it can appear in results. Crawling is the act of fetching pages by following links. Redirect sends visitors from one address to another. Structured data is markup that describes a page to machines. HSTS is a header that tells browsers to always use https. TTFB is how long the server takes to start replying.
Why the audit shows both failures and passes
A list of problems alone can feel discouraging and hides what is working. Showing every check, including the ones that passed, tells you what you can safely leave alone and gives you a baseline. When a passed check later turns into a failure, you will know that something changed, and you can look at what was deployed around that time.
How checks are weighted
Not every check matters equally. A missing https certificate or a noindex tag on an important page can remove a site from search, so those carry more weight than a missing favicon. Each category score is the severity-weighted share of its checks that ran, and checks that affect only a few pages cost less than ones that affect many. The result is a score that reacts sensibly: a handful of small warnings leaves you in the high eighties, while one critical failure pulls a category down fast.
All checks
- HTTP-001 · Broken or missing pageRestore the page, or redirect it to the closest working page.
- TITLE-001 · Missing page titleWrite a short, clear title that says what the page is about.
- TITLE-002 · Title too longShorten it. Put the most important words first.
- TITLE-DUP · Duplicate titlesGive each page its own title that says what makes it different.
- META-001 · Missing meta descriptionWrite 1 to 2 sentences describing the page and inviting the click.
- META-DUP · Duplicate meta descriptionsWrite a unique 1 to 2 sentence summary for each important page.
- H1-001 · Missing or multiple H1 headingsUse exactly one main heading matching the page topic.
- CANON-001 · Missing canonical tagAdd a tag pointing to the main version of the page.
- IMG-001 · Images missing alt textWrite one short sentence describing each picture.
- CONTENT-001 · Thin contentAdd helpful details and examples: or merge with a sibling page.
- PERF-001 · Heavy pageCompress images to WebP/AVIF and lazy-load below-the-fold content.
- SOCIAL-001 · Missing preview imageAdd one wide preview picture (1200×630).
- LINK-ORPHAN · Orphan pageLink it from a related page using descriptive words.
- NOIDX-001 · Page set to noindexRemove the noindex from money pages; keep and document it on utility pages.
- MOBILE-001 · Missing viewport tagAdd <meta name=viewport> to the page template.
- H2-001 · Skipped heading levelsReorder headings so levels step down one at a time.
- HREFLANG-001 · Invalid hreflang codesUse ISO codes: language lowercase, region UPPERCASE.
- IMG-002 · Images missing dimensionsAdd width and height matching the real image size.
- MIXED-001 · Mixed contentServe every subresource over https.
- SCHEMA-002 · Schema missing required fieldsAdd the missing properties with values matching visible content.
- SCHEMA-003 · Broken JSON-LD syntaxValidate in the Rich Results Test and fix the syntax error.
- TRAIL-001 · Duplicate URL variantsPick one URL form, redirect the other, keep canonicals consistent.
- ANCHOR-001 · Generic anchor textRewrite with 2 to 5 words describing the target page.
- CONTENT-DUP · Near-duplicate pagesDifferentiate each page or merge them with a redirect.
- SITEMAP-001 · Broken URLs in sitemapRegenerate the sitemap from live URLs only and resubmit.
- SITEMAP-002 · Sitemap missing lastmodEmit real modification dates in lastmod.
- ROBOTS-001 · No sitemap in robots.txtAdd a Sitemap: line with the absolute sitemap URL.
- ROBOTS-002 · robots.txt blocks CSS/JSAllow resource paths while keeping admin areas blocked.
- BROKEN-001 · Broken internal linksPoint each link at the live URL or remove it.
- KEY-001 · Target phrase missing from key spotsWork the phrase into title, H1 or intro: naturally.
- CHARSET-001 · Missing character encodingAdd <meta charset="utf-8"> as the first tag in the head.
- LANG-001 · Missing page languageAdd lang="en" (or your language code) to the html tag.
- DEPR-001 · Deprecated HTML tagsReplace old tags such as font or center with semantic HTML and CSS.
- EMAIL-001 · Plain-text email addressUse a contact form or hide the address from scrapers.
- BLANK-001 · Unsafe target=_blank linksAdd rel="noopener noreferrer" to links that open a new tab.
- DOM-001 · Very large page structurePaginate long lists and flatten unnecessary wrapper elements.
- REFRESH-001 · Meta refresh redirectUse a server-side 301 redirect instead.
- RENDER-001 · Render-blocking scriptsAdd defer or async to scripts in the head.
- SOCIAL-002 · Missing Twitter/X card tagAdd twitter:card=summary_large_image.
- SOCIAL-003 · Incomplete Open Graph tagsAdd og:title and og:description next to og:image.
- HTTPS-001 · Site not served over HTTPSInstall a free certificate and redirect everything to https.
- HTTPS-002 · http does not redirect to httpsAdd a permanent redirect from http to https.
- HSTS-001 · No HSTS headerSend Strict-Transport-Security once https works everywhere.
- TLS-001 · Certificate problem or near expiryRenew the certificate and enable auto-renewal.
- TLS-002 · Outdated TLS versionAllow TLS 1.2 and 1.3 only.
- HTTP2-001 · HTTP/2 not enabledEnable HTTP/2 (or HTTP/3) on the server or CDN.
- WWW-001 · www and non-www both serve the siteRedirect one hostname to the other with a 301.
- COMPRESS-001 · No text compressionEnable gzip or brotli for HTML, CSS and JavaScript.
- TTFB-001 · Slow server responseCache pages at the edge and speed up server code.
- CACHE-001 · Weak browser cachingServe static files with a long Cache-Control max-age.
- SEC-001 · Missing security headersAdd X-Content-Type-Options, Referrer-Policy and a CSP or X-Frame-Options.
- SEC-002 · Server version disclosedHide version numbers in Server and X-Powered-By.
- NOTFOUND-001 · Soft 404 or bare 404 pageReturn a real 404 status with a helpful page.
- SPF-001 · No SPF recordPublish an SPF TXT record if the domain sends email.
- FAVICON-001 · No faviconAdd a square icon and link it in the head.
- ANALYTICS-001 · No analytics detectedInstall an analytics tool and connect Search Console.
- SITEMAP-003 · No XML sitemapGenerate sitemap.xml and submit it in Search Console.
- ROBOTS-003 · No robots.txtAdd a simple robots.txt with a Sitemap line.
- REDIR-001 · Redirect chainRedirect each old URL straight to its final page.
Fixing issues safely
Change one thing at a time, note what you changed and re-run the audit to confirm the finding has cleared. Be careful with changes to robots.txt, redirects and canonical tags, because mistakes there can hide whole sections of a site from search engines. Test a sample of URLs by hand before and after, and keep a backup of the previous settings.
For deeper reading, see the guides on technical SEO, on-page SEO, off-page SEO and AI SEO.