Run a free on-page SEO audit on any URL. Analyze 70+ ranking factors across meta tags, headings, social tags, structured data, accessibility, readability, and AI search readiness — with actionable fix recommendations.
Written by Ishan Karunaratne, full-stack developer and SEO engineer building DNS and web analysis tools since 2024. · Last reviewed:
An on-page SEO checker is a tool that analyzes a single web page to evaluate how well it is optimized for search engine rankings. It examines HTML elements that search engines use to understand, index, and rank the page — including the title tag, meta description, heading hierarchy, canonical tags, Open Graph tags, structured data (JSON-LD), image alt text, internal links, content readability, and technical factors like HTTPS, viewport configuration, and render-blocking resources. A comprehensive on-page SEO audit identifies specific issues and provides actionable recommendations to improve search visibility.
DNSChkr's free on-page SEO checker performs 70+ individual checks across 12 categories, including areas that most SEO tools miss: accessibility auditing (WCAG 2.2 landmark and form label checks), render-blocking script detection, mixed content identification, deprecated HTML flagging, and AI search readiness scoring (GEO/citability analysis for Google AI Overviews, ChatGPT, and Perplexity citations). Results include SERP previews, social share previews, heading tree visualization, and structured data syntax highlighting.
Every on-page SEO audit should cover these 12 categories. This tool checks all of them automatically when you enter a URL:
Title presence and length (30-60 chars), meta description (120-160 chars), robots directives, viewport, charset declaration.
H1 presence and count, first heading position, H1 length, H2 presence, empty headings, hierarchy validation. JS framework-aware.
og:title, og:description, og:image, og:url, og:type. Includes Facebook share preview rendering.
twitter:card, twitter:title, twitter:description, twitter:image. Includes X card preview rendering.
Presence, absolute URL validation, self-referencing detection, cross-domain canonical warnings.
JSON-LD, Microdata, and RDFa detection. JSON syntax validation and @type declaration check.
Internal/external link counts, broken hrefs, generic anchor text, nofollow ratio, excessive link warnings.
Alt text coverage, width/height for CLS prevention, lazy loading usage, alt text length validation.
Word count (thin content detection), text-to-HTML ratio, paragraph structure, Flesch-Kincaid readability grade.
DOCTYPE, html lang, favicon, HTTPS, DOM size, hreflang, render-blocking scripts, async/defer analysis, resource hints, mixed content, deprecated HTML, iframes.
Main landmark, nav landmark, skip navigation link, form labels (WCAG SC 1.3.1), tabindex misuse detection.
Citability score, optimal passage length (134-167 words), question headings, FAQ sections, author signals, publication dates, structured content analysis.
Most on-page SEO tools are either paid, limited in scope, or require installing software. Here is how DNSChkr's free on-page SEO checker compares:
| Feature | DNSChkr | Ahrefs Toolbar | Screaming Frog | SEMrush |
|---|---|---|---|---|
| Free to use | Yes | Yes | 500 URLs | Paid |
| No install required | Yes | Extension | Desktop app | Yes |
| SERP + social previews | Yes | Partial | No | Partial |
| Heading hierarchy tree | Yes | Yes | Yes | No |
| Structured data validation | Yes | Yes | Yes | Yes |
| Readability scoring | Yes | No | No | Yes |
| Render-blocking detection | Yes | No | Yes | No |
| Accessibility checks | Yes | No | No | No |
| AI search readiness (GEO) | Yes | No | No | No |
| Free API access | Yes | No | No | No |
On-page SEO refers to the optimization of individual web pages to improve their search engine rankings and attract organic traffic. Unlike off-page SEO (backlinks, social signals) or technical SEO (site speed, crawlability), on-page SEO focuses on the content and HTML source code of a specific page. According to Google's SEO Starter Guide, the title tag is one of the most important signals for understanding what a page is about.
The key elements of on-page SEO include: the title tag (the most important single ranking factor for a page), the meta description (influences click-through rate from search results), heading hierarchy (H1-H6 tags that structure content per the W3C page structure guidelines), canonical tags (prevent duplicate content issues), structured data (enables rich results in search), internal linking (distributes page authority and helps crawlers discover content), image optimization (alt text, dimensions), and content quality (depth, readability, relevance).
As of 2026, on-page SEO also includes optimizing for AI search engines. Google AI Overviews, ChatGPT web search, and Perplexity now cite web pages directly in their responses. Pages with clear, structured, authoritative content are significantly more likely to be cited — making on-page optimization more important than ever.
Trace HTTP redirect chains visually with TLS certificate and security header analysis.
Validate and parse robots.txt crawl rules for any domain.
Analyze HTTP security headers and get a letter grade with fix recommendations.
Validate SPF records with DNS lookup limit analysis and RFC 7208 compliance checking.