HTML Checker: Headings, Meta Tags, JSON-LD

How to use

Open the page in your browser and copy everything from “View page source” (Ctrl+U / ⌘+Option+U).
Paste it into “HTML source” or open a saved .html file.
Optionally enter the page URL to separate internal and external links.
Check the score and findings in “Overview”, then the Headings, Meta & social, Links, Images and Structured data tabs.

What it does

SEO basics in one pass

Title and description length (accounting for wide CJK characters), duplicate or relative canonicals, noindex, viewport, lang, hreflang x-default and meta refresh.

Heading outline

h1–h6 shown as an indented tree, highlighting a missing h1, skipped levels and empty headings.

Images, links and forms

Counts and lists images without alt or width/height (a CLS cause), links without text, unnamed buttons, unlabeled fields and duplicate ids.

Structured data and social previews

Parses JSON-LD, lists @types and shows syntax errors. Shows Open Graph / Twitter tags and an approximate search and social preview.

Safe analysis

HTML is loaded as an inert document in your browser: scripts never run and external resources are never fetched.

Use cases

Catch missing title, description, canonical or Open Graph tags before launch
Check that headings (h1–h6) are properly nested
Find images without alt text and links without text
Validate JSON-LD syntax and see which @types are present
Review HTML delivered by an agency using only your browser

Supported formats

Input

HTML (paste or .html / .htm file)

Capability matrix

Feature	Support	Notes
title, description, canonical, robots, Open Graph	Supported	—
Heading structure, image alt, links, forms	Supported	—
JSON-LD syntax check and @type list	Supported	—
Schema.org required-property validation (rich result eligibility)	Not supported	—
Content rendered by JavaScript	Partial	Only what is in the pasted HTML
Fetch a page by URL / check broken links	Not supported	Paste the source instead

Limits & notes

Pages are not fetched. Copy the HTML from “View page source”. For JavaScript-rendered content, copy the HTML from the Elements panel of the developer tools.
Files up to 10 MB; link and image tables show up to 1,000 rows.
The score subtracts 12 per error and 5 per warning — a rough guide, not a ranking signal.
Images such as og:image are shown as URLs only, so no third-party server is contacted.

Privacy & safety

The HTML you paste is analysed in your browser only and never sent to a server. Scripts are not executed and external resources are not loaded.

FAQ

How long should the title and meta description be?

Roughly 50–60 characters for titles and 120–160 for descriptions in English (Japanese about half). Longer text is truncated in results; this tool accounts for wide CJK characters.

Should a page have only one h1?

Several are not an error, but one h1 stating the topic keeps the structure clear. Also avoid skipping levels (h2 followed by h4).

Do decorative images need alt?

They need the attribute: use alt="" so screen readers skip them. This tool only flags images with no alt attribute at all.

Can it check content rendered by JavaScript?

Not from “View source”. Copy the <html> element from the Elements panel in the developer tools and paste that to inspect the rendered page.

Is the HTML I paste sent anywhere?

No. Analysis runs entirely in your browser and nothing is sent to a server.

robots.txt Tester

Paste a robots.txt to see instantly whether a URL is allowed or blocked for Googlebot or AI crawlers, and which line decided it. Misspellings and directives Google ignores are flagged too.

No upload

XML Sitemap Generator & Validator

Paste a list of URLs to create a correctly written sitemap.xml, or paste an existing sitemap to find the errors that stop Google from reading it — with line numbers.