Search engines read your pages as text, but they understand them best when you label what the text means. Schema markup is that labelling. It is a shared vocabulary for describing the things on a page — an article, a product, a recipe, an FAQ — in a way machines can act on. Done well, it helps search engines represent your content accurately and can unlock richer listings.
What structured data is
Structured data is information added to a page specifically for machines, describing the entities the page is about. Instead of leaving a search engine to infer that a block of text is a set of questions and answers, you state it explicitly: this is an FAQ, here are the questions, here are the answers. The vocabulary most search engines use comes from a shared project called Schema.org, which defines types like Article, Product, Organization, and Event, along with the properties each can have.
JSON-LD, the preferred format
Schema can be expressed in a few ways, but the one search engines recommend is JSON-LD. It is a block of JSON, placed in the page, that describes the entities separately from the visible HTML. Keeping it separate is a real advantage: you are not weaving attributes through your markup, so the description is easy to read, generate, and maintain. A single script block can describe several connected entities at once.
How a graph fits together
Real pages are about more than one thing. A blog post has an author, belongs to a site, sits within a breadcrumb trail, and may include an FAQ. Structured data models this as a graph of connected nodes: an Organization, a WebSite, a BreadcrumbList, the Article itself, and a FAQPage, each referencing the others. Thinking in terms of a graph — entities and the relationships between them — is the key to describing a page faithfully rather than as a bag of disconnected labels.
Where rich results come in
Some structured data can make a page eligible for enhanced search listings — an FAQ that expands directly in the results, review stars, a recipe’s cooking time. It is important to be clear-eyed here: marking up a page makes it eligible, but the search engine decides whether to show a rich result, and eligibility is never a guarantee. The markup must also reflect content genuinely visible on the page; describing things that are not there breaks the rules and can lead to penalties.
Getting it right
A few principles keep schema honest and effective. Describe only what is actually on the page. Use the most specific type that fits — Article rather than a vague generic, and a more specific article subtype where appropriate. Fill in the properties a type expects rather than the bare minimum. And keep the structured data in step with the page as it changes, so the two never contradict each other.
Validate before you trust it
Structured data is easy to get subtly wrong — a mistyped property, a missing required field, a value in the wrong format. Because the markup is invisible to visitors, those errors can sit unnoticed. Running a page through a structured-data validator confirms the syntax is sound and the required properties are present. It cannot promise a rich result will appear, but it does confirm you have described the page in a way machines can read.