What does the SEO Structure Sniffer check?

It reports heading counts for H1, H2, and H3, identifies images that are missing alt text, and counts internal versus external links in the HTML you paste.

Why does having more than one H1 matter?

A single, clear H1 helps search engines and screen readers identify the main topic of a page. Multiple H1s can dilute that signal, so the heading counts make it easy to spot when a page has too many.

Why is missing alt text a problem?

Alt text describes an image for screen-reader users and gives search engines context about the image. Images without it are both an accessibility gap and a missed SEO signal.

Does this tool crawl my live site?

No. It only analyzes the HTML you paste in. It doesn't fetch URLs, follow links, or load external resources, which is why it works on staging and internal pages too.

Is the HTML I paste sent anywhere?

No. All parsing happens locally in your browser, so the markup you paste is never uploaded or stored.

SEO Structure Sniffer

Quickly analyze pasted HTML for basic on-page SEO structure: heading counts (H1, H2, H3), missing image alt text, and internal/external link counts. Paste HTML source code below to get a quick analysis.

HTML & Base URL

Paste HTML source code and provide the page's Base URL for accurate link analysis.

Base URL (for Link Analysis)

HTML Source Code

Analysis Results

Basic SEO structure checks.

Paste HTML on the left to see analysis.

Analysis Rules

This tool performs basic checks based on common SEO guidelines.

H1 Tag:
A page should ideally have exactly one <h1> tag representing the main topic or title. Warnings appear if zero or more than one is found.

Heading Hierarchy [H2-H6]:
Headings should create a logical outline. Levels should not be skipped (e.g., using an <h3> directly after an <h1> without an intermediate <h2>). This tool checks for direct level skips.

Image Alt Text:
All relevant images (<img> tags) should have descriptive alt text for accessibility and search engines. Purely decorative images can use an empty alt="". This tool checks for missing or empty `alt` attributes.

Internal/External Links:
Checks the ratio of links pointing within the same domain versus linking out. A good internal structure helps navigation and distributes link equity. Accurate classification requires providing the Base URL.

Note: This tool provides basic structural checks. Comprehensive SEO involves many other factors like content quality, keywords, site speed, backlinks, mobile-friendliness, and technical setup.

Learn more at Google Search Central

About SEO Structure Sniffer

Most on-page SEO problems are structural and invisible at a glance: a page with two H1s, headings that skip levels, images with no alt text, or a link profile that's almost entirely external. These issues rarely show up when you look at a rendered page, but they shape how search engines and assistive technology read it.

This tool takes raw HTML — whatever you paste from view-source, a template, or a build output — and reports the structure that matters. It counts your H1, H2, and H3 headings, flags images that are missing alt text, and tallies internal versus external links so you can see the shape of the page at a glance.

It's a fast sanity check, not a full crawl: paste markup, read the counts, and catch the obvious problems before they ship. Parsing happens entirely in your browser, so the HTML you paste — including anything from staging or internal pages — never leaves your machine.

How to use SEO Structure Sniffer

Copy your page HTML
Grab the HTML source of the page you want to check — from view-source, your CMS, or a template file.
Paste it into the tool
Drop the markup into the input area. The full document or a fragment both work.
Read the structure report
Review the heading counts, the list of images missing alt text, and the internal versus external link tally.
Fix and re-check
Adjust your markup to resolve any issues — a single H1, descriptive alt text, sensible heading order — then paste it again to confirm.

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