On-Page SEO Checker — Find and fix page tag issues
Weak titles, missing meta descriptions, duplicate H1s and broken canonicals quietly cost rankings and clicks. Paste a URL or HTML to audit title, H1, meta description, canonical, Open Graph, JSON-LD, mixed content and render-blocking, each with a fix suggestion. Paste mode runs on your device; URL mode fetches the page once without storing it. Example: a sample page with a duplicate H1 and one http:// image.
How it works
The checker parses the markup you paste (or the HTML fetched from a URL) and evaluates a fixed list of on-page SEO checks. Each check reads a single kind of tag: the title, the meta description, H1 tags, the canonical link, robots meta, Open Graph fields, JSON-LD blocks, mixed content and render-blocking resources. Paste mode runs entirely in your browser; URL mode fetches the page once through our worker and does not store it.
Rules the checks follow
These are the standards each check compares against. They come from Google Search Central and the HTML specification.
- Title: a page should have one descriptive <title>. Google may rewrite it, but a concise title near 50–60 characters usually displays well.
- H1: use exactly one H1 that states the page topic. Additional headings should be H2–H6 and form a logical outline.
- Canonical: a self-referencing canonical tells Google which URL is the preferred one when duplicates exist. Link rel="canonical" goes in <head>.
- Mixed content: an https page referencing http:// resources is blocked by browsers. This check lists those references as warnings.
- Render-blocking: a stylesheet in <head> without a media attribute blocks rendering. This check is heuristic and does not measure real load time.
Example
Sample input is a page with a 71-character title, no meta description, two H1 tags, a canonical to another URL, one og:image, a valid JSON-LD block and one http:// image. The checker reports the title as likely truncated, H1 as a warning, canonical as non-self-referencing, and mixed content as a warning, matching what the tool shows when you load the sample.
Good fits
- Before a redesign or relaunch: run the same page through the checker and fix the reported issues in one pass.
- Template handoff: when you receive HTML from an agency or a page builder, verify the head tags instead of trusting the export.
- Content updates: after a CMS edit, confirm the title, description and canonical still match the new page.
Frequently asked questions
What does an on-page SEO checker look for?
It checks the tags a page controls itself: the title, meta description, H1, canonical, robots meta, Open Graph fields, JSON-LD structured data, mixed content and render-blocking resources. It does not measure rankings or backlinks.
Why should a page have exactly one H1?
A single H1 states the topic of the page clearly for both readers and search engines. Multiple H1s blur the outline; use one H1 and structure the rest with H2–H6.
Does canonical have to point to itself?
For the page that should rank, yes — a self-referencing canonical is the clearest signal. Pointing canonical at another URL tells Google that page is a duplicate, which is useful only when that is true.
Why does the checker flag http:// resources as mixed content?
When a page is served over https and references http:// images, scripts or styles, browsers block the request by default. This check lists those references as warnings so you can switch them to https.
Does the JSON-LD check test validation?
It verifies the blocks parse as valid JSON and reminds you to keep structured data consistent with visible content. It does not run a full schema.org validator.
Is my HTML uploaded anywhere?
No. When you paste HTML, parsing happens on your device and nothing is sent to a server. URL mode fetches the page once through our worker and does not store it.
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