What structured data actually does
Search engines read your page as text and make educated guesses about what it means. Structured data removes the guessing: it states explicitly that this string is a business name, that one is a postcode, and this number is an opening hour — in a vocabulary (schema.org) that Google, Bing, Yahoo and Yandex jointly maintain.
The payoff is rich results. Correct structured data is what lets a recipe show a star rating in search, an event show its date, or a local business appear with its address and hours in a knowledge panel. Those enhanced listings occupy more space and attract more clicks than a plain blue link.
Why JSON-LD rather than Microdata
There are three ways to add structured data, and Google explicitly recommends JSON-LD. Unlike Microdata and RDFa, which scatter attributes throughout your HTML, JSON-LD sits in a single <script> block — usually in the <head> — completely separate from your markup.
That separation is the whole advantage. You can restructure your HTML without breaking your structured data, generate it server-side independently of your templates, and read it as one coherent object rather than reverse-engineering it from attributes spread across a page.
The rule that gets sites penalised
Structured data must describe content that is actually visible on the page. Marking up a review rating that appears nowhere, or listing opening hours you don't display, violates Google's structured data guidelines and can trigger a manual action that removes your rich results entirely — sometimes site-wide.
This is the most common way well-intentioned SEO work backfires. The safe rule: if a user can't see it on the page, don't put it in the schema.
Testing and building up
Always validate before shipping. Google's Rich Results Test shows which rich result types your markup qualifies for, and the Schema Markup Validator at validator.schema.org catches syntax errors and unrecognised properties. Search Console then reports errors it finds across your live site.
Start small. A correct LocalBusiness or Organization block with name, URL, logo and address delivers most of the value. Once that's validating cleanly, layer on the types that fit your content — FAQPage for question sections (this site uses it on every page), BreadcrumbList for navigation trails, Article for posts. Each type has required and recommended properties; missing a required one disqualifies the whole block, which is exactly what the validators are for.