structured data

What it is

A page says one thing to a reader and another to a parser. The prose says “I charge from 1600 zł and reply within two hours”; the structured data says the same thing as typed fields — an Offer with a price, an organisation with a LocalBusiness type and an address — in a script tag the visitor never sees.

Almost everyone uses JSON-LD for it, and schema.org is the shared vocabulary that makes one site’s Article mean the same as another’s.

Why it matters if you are paying for a website

Two reasons, and they are pulling further apart every year.

The old one is rich results: stars, prices, FAQ accordions, breadcrumbs in the search listing. Worth having, never guaranteed — Google decides, and it has withdrawn whole result types before.

The newer one is that structured data is how a machine that is not a search engine works out what your business is. A model summarising your company reads the same markup, and it is far more reliable at reading typed fields than at inferring facts from marketing copy.

What almost nobody does

Validate the graph rather than the snippets.

The testing tools check one block at a time: is this Article well-formed? What they do not check is whether the blocks on a page agree with each other — whether the author your Article points at is actually defined anywhere, whether two nodes claim the same identifier, whether the identifiers stay stable between pages. Sites accumulate JSON-LD from three plugins that have never been introduced to each other, and the result parses, passes the snippet test and describes nobody.

On this site the whole page is one graph with stable identifiers, and the build fails on a dangling reference: if a node points at an @id that no node on that page defines, no deploy happens. That check exists because the failure is completely invisible otherwise — the markup looks fine, the test tool is happy, and the page says nothing coherent about who wrote it.

What structured data is not

It is not a ranking factor, and adding it does not make a page rank. It is also not a place to put claims the page does not make: marking up prices, reviews or availability that do not appear to a visitor is what the spam policies call structured data abuse, and it is one of the few SEO mistakes with a manual penalty attached.