Microdata is a syntax for embedding machine-readable metadata inside HTML documents using attributes like itemscope, itemtype, and itemprop. Unlike JSON-LD, which isolates structured data in a script block, Microdata intertwines annotations with visible content, allowing search engines to parse semantic meaning directly from the DOM. It relies on the Schema.org vocabulary to define entity types and properties.
Glossary
Microdata

What is Microdata?
Microdata is an HTML specification used to nest structured data directly within existing page content using tag attributes, serving as an alternative to JSON-LD for annotating entities.
While historically significant, Microdata has been largely superseded by JSON-LD as Google's recommended serialization format due to JSON-LD's cleaner separation of concerns and easier dynamic injection. However, Microdata remains relevant for legacy systems and specific use cases where tight coupling between visible text and structured markup is required for entity linking and semantic HTML authoring.
Microdata vs. JSON-LD vs. RDFa
A technical comparison of the three primary syntaxes for implementing Schema.org structured data markup on web pages.
| Feature | Microdata | JSON-LD | RDFa |
|---|---|---|---|
W3C Recommendation Status | Completed (HTML5) | Completed (JSON-LD 1.1) | Completed (HTML+RDFa 1.1) |
Google Preferred Format | |||
Markup Location | Inline within HTML body | Standalone script block in head or body | Inline within HTML body |
Separation of Concerns | Mixed with content markup | Cleanly separated from content | Mixed with content markup |
Ease of Manual Authoring | Moderate | High | Low |
Dynamic Injection via JavaScript | |||
Supports @id Node Referencing | Limited (itemid) | ||
Supports All Schema.org Types |
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Frequently Asked Questions
Clear, technical answers to the most common questions about implementing HTML Microdata for structured data markup and AI-driven search visibility.
Microdata is an HTML5 specification that allows you to nest machine-readable structured data directly within the existing content of a web page using specific tag attributes. It works by annotating HTML elements with itemscope, itemtype, and itemprop attributes to define entities and their properties. When a search engine or AI parser crawls the page, it extracts these annotations to understand the semantic meaning of the content—such as identifying a person's name, a product's price, or an event's location—without requiring a separate data block. Unlike JSON-LD, which lives in a <script> tag in the document head, Microdata is interwoven with the visible markup, making it a direct, inline method for declaring structured entities.
Related Terms
Explore the core structured data formats, properties, and types that form the foundation of modern entity-based SEO and generative engine optimization.
RDFa
An HTML5 extension providing attribute-level markup for embedding rich metadata directly within web documents. RDFa uses attributes like vocab, typeof, and property to express linked data triples within existing page content. It bridges the gap between Microdata's simplicity and RDF's expressive power, supporting vocabularies beyond Schema.org.
@id
A JSON-LD keyword assigning a globally unique Internationalized Resource Identifier (IRI) to an entity. This enables unambiguous node identification across a knowledge graph, allowing multiple structured data blocks to reference the same entity without duplication. Essential for connecting a WebSite to its Organization and Person nodes.
SameAs Property
A Schema.org property establishing an equivalence relationship between a local entity and its canonical URLs on external authoritative knowledge bases. Common targets include Wikipedia, Wikidata, and Crunchbase. Explicit sameAs links help AI models disambiguate entities and consolidate authority signals across the semantic web.
MainEntity
A Schema.org property identifying the primary, most prominent entity described on a web page. When a page contains multiple entities—such as an article about a product—mainEntity disambiguates the central topic for search engines. Critical for preventing AI overviews from misidentifying secondary content as the page's focus.
ClaimReview
A Schema.org type used to fact-check a specific statement, indicating the claim's author, the review's verdict, and the source of the assessment. Supported verdicts include True, False, MostlyTrue, and Misleading. Essential for publishers seeking to have fact-checks displayed prominently in Google News and AI-generated summaries.

About the author
Prasad Kumkar
CEO & MD, Inference Systems
Prasad Kumkar is the CEO & MD of Inference Systems and writes about AI systems architecture, LLM infrastructure, model serving, evaluation, and production deployment. Over 5+ years, he has worked across computer vision models, L5 autonomous vehicle systems, and LLM research, with a focus on taking complex AI ideas into real-world engineering systems.
His work and writing cover AI systems, large language models, AI agents, multimodal systems, autonomous systems, inference optimization, RAG, evaluation, and production AI engineering.
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