Three formats, and the raw block
Extraction, not validation. The difference matters and it is stated further down.
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JSON-LD, microdata and RDFa
Three formats, not one. Most free extractors read JSON-LD and stop, which makes an older site or a shop on an older platform look like it has no structured data at all.
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One row per block, with its type
A page with an Organization block, a BreadcrumbList and two FAQPage entries gets four rows, not one summary line.
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The raw JSON in the export
The whole block, not a description of it, so you can diff what shipped against what you meant to ship.
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Parse failures flagged, not dropped
A malformed block is reported as malformed. Silence would be the same output as a page with no markup, and those are very different situations.
Five findings hiding in the rows
Structured data fails quietly. Nothing breaks, nothing warns, the rich result simply never appears.
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A page with no blocks where the template should have added some
One product page out of twenty-five with an empty schema column is a template condition somebody wrote and forgot.
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A block that will not parse
Usually a stray comma or an unescaped quote from a templating engine. The markup is on the page, it looks right in the source, and it counts for nothing.
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Types that do not match the page
A Product block on a category listing, an Article block on a contact page. Templates apply the same block everywhere far more often than they should.
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Two blocks describing the same thing
A plugin and a theme both adding an Organization block is common, and the two rarely agree about the name, the logo or the phone number.
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Markup that contradicts the visible page
The rule is that structured data describes what is on the page. A price, a rating or a date in the JSON that a visitor cannot see is the kind of thing manual actions are written about.
What it will not tell you
Stated here rather than discovered later.
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It extracts, it does not validate
You get the types and the raw JSON. Whether a block satisfies Google's requirements for a particular rich result is a separate question, and Google's Rich Results Test is the authority on it.
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No rich result preview
There is no picture of what the listing might look like. That is a rendering question and it belongs to the search engine, not to an extractor.
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Static HTML only
Structured data injected by a tag manager after load is not in the HTML the server sent. How reliably that gets picked up in the wild is its own long-running argument.
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Twenty-five URLs per run
It runs in a browser tab. Enough to check a template across a section, not to inventory a catalogue.
Reasonable questions
Which format should I use: JSON-LD, microdata or RDFa?
Google recommends JSON-LD and it is the easiest to maintain, because it sits in one block rather than being woven through the markup. Microdata and RDFa still work, and there is rarely a reason to start with them now.
Does structured data improve rankings?
Not on its own. Google has been consistent that it is not a ranking factor. It makes a page eligible for rich results, which changes how a listing looks and how often it is clicked.
Why does this show blocks that Google's testing tool does not?
This extracts everything on the page, including formats and types Google does not use for rich results. Google's tool reports what it can act on, which is a deliberately narrower list.
Can I mark up something that is not visible on the page?
No. Google's guidelines require structured data to describe content a visitor can see. Marking up prices, reviews or dates that are not on the page is the most common cause of a structured data manual action.
Structured data is one tab of the checker
The same run returns titles, meta descriptions, headings, word counts, links and images as well. It is one tool with seven tables and seven CSV exports, not seven separate tools you have to run one after another.
Other checks the same tool runs: Bulk SEO checker, Meta tag checker, Heading checker, Alt text checker, Word count checker, Canonical checker, Open Graph checker