Which format should we use?

JSON-LD where the site's setup allows it, which is what Google recommends on the grounds that it is the easiest solution. Microdata and RDFa are also supported, so an existing implementation in either is not something to rush into replacing.

We added markup and nothing appeared. Why?

Most often because required properties are missing: all of them have to be present for an object to be eligible. The other reason is that eligibility is not appearance, and the decision to show anything sits with whoever is displaying it.

Does it matter for AI answers as well as search results?

The documented behaviour concerns search appearance specifically, and the underlying argument is broader than that: machines reading your pages cannot infer from layout what a person infers instantly, so saying explicitly what a page contains helps anything at all that reads it.

Glossary

Structured data

Machine-readable markup describing what a page contains, so a machine reading it knows whether it holds a product, a question and answer, or a definition.

In plain terms

Labels on a page that a machine can read, saying what the page is about. A person can see that a block of text is a price or an opening time; a machine cannot, unless somebody has said so in a form it understands.

Why it matters

Because more of what reads your pages is now software rather than people, and software cannot infer from layout what a person infers instantly. Saying explicitly what a page contains is the cheapest thing you can do about that, and it is a one-off piece of work.

How it works

It is a standardised way of describing a page and classifying what is on it. The description sits alongside the visible content and says what the parts are, rather than adding anything a reader sees.

Most of it uses a shared vocabulary called schema.org, which is what makes it interoperable. The value comes from everybody describing a price or an author the same way, so the words are not yours to choose.

Three formats are supported and one is recommended. JSON-LD, Microdata and RDFa are all read, and JSON-LD is what Google recommends where a site's setup allows it, on the grounds that it is the easiest to work with.

Completeness decides eligibility. All the required properties for an object have to be present for it to be eligible for enhanced display, so a partial description is frequently the reason nothing appears despite the markup being there.

Eligible is not the same as shown. The word in the guidance is eligibility, and treating markup as a mechanism that produces a particular appearance is how disappointment happens, because the decision to show anything is not yours.

It describes what is already on the page, and that is a constraint rather than a formality. Markup asserting something the visible content does not support is a misrepresentation of your own page, and it is the kind that is trivially detectable by whoever is reading it.

It is a one-off with an ongoing edge. Adding it to a template covers every page of that kind at once, and the maintenance is remembering that a redesign which changes where a price lives can leave the description pointing at something that has moved.

What a page says to a person and to a machine

The reason this is worth the small effort is that the proportion of readers who are software has been rising steadily and nothing about that is reversing. A page written entirely for people is not wrong, it is simply relying on a shared visual grammar that only people have, and the cost of also saying the same things in a form machines read is an afternoon of work per site rather than an ongoing programme. The discipline that keeps it useful is narrower than the effort of adding it: when a template changes, check that the description still points at what it claims to. Markup describing a price that moved during a redesign is worse than no markup, because it is confidently wrong rather than absent, and nothing in the visible page will ever look broken to the person who made the change.

Seen in the wild

A definition page describing itself as a definition, so a machine reading it knows.
Perplexity
Markup added to a template, covering every page of that type at once.
Writer
A page whose markup describes a price that a redesign moved elsewhere.
Glean

Common misconceptions

People assume

Adding it improves ranking.

In fact

The documented effect is eligibility for enhanced display, and the guidance is careful about that word. Treating markup as a ranking lever confuses being describable with being preferred, which are different things.

People assume

Any reasonable description works.

In fact

The value comes from a shared vocabulary that everybody uses the same way, so the terms are not yours to invent. A bespoke description is readable by nothing and does the job of neither prose nor markup.

Questions

Which format should we use?: JSON-LD where the site's setup allows it, which is what Google recommends on the grounds that it is the easiest solution. Microdata and RDFa are also supported, so an existing implementation in either is not something to rush into replacing.
We added markup and nothing appeared. Why?: Most often because required properties are missing: all of them have to be present for an object to be eligible. The other reason is that eligibility is not appearance, and the decision to show anything sits with whoever is displaying it.
Does it matter for AI answers as well as search results?: The documented behaviour concerns search appearance specifically, and the underlying argument is broader than that: machines reading your pages cannot infer from layout what a person infers instantly, so saying explicitly what a page contains helps anything at all that reads it.