Format, beautify, validate, and minify XML documents instantly in your browser. Catch malformed tags, choose your indent size, and download clean, readable XML.
XML (Extensible Markup Language) is a text-based markup language designed to store and transport structured data in a format that's both human-readable and machine-parseable. Unlike HTML, which uses a fixed, predefined set of tags for describing web page layout, XML lets you define your own tag names to describe whatever data you're representing — <invoice>, <customer>, and <lineItem> are all equally valid, because XML cares about structure and well-formedness, not about which specific tag names you choose.
XML became the dominant data-interchange format of the late 1990s and 2000s, powering everything from SOAP web services and RSS feeds to configuration files, Microsoft Office document formats (.docx and .xlsx are internally XML), and Android UI layouts. While JSON has since overtaken XML as the default choice for most modern REST APIs due to its more compact syntax, XML remains deeply embedded in enterprise systems, document standards, and any context that benefits from its richer feature set — namespaces, schemas, attributes, and mixed content.
Raw XML — especially from a minified API response, a database export, or a build artifact — is often delivered as a single unbroken line with no spacing, which is efficient for machines to transmit but nearly unreadable for a human trying to understand or debug it. Formatting (also called 'pretty-printing') adds consistent indentation and line breaks so that the nesting structure of elements becomes visually obvious at a glance: you can immediately see which elements are children of which, how deeply something is nested, and where a repeated block starts and ends.
Formatting is especially valuable when debugging a SOAP request or response, reviewing a configuration file before deploying it, comparing two XML documents for differences, or simply understanding a data structure you didn't author yourself. It also makes structural errors far easier to spot — a missing closing tag is easy to miss in a single-line 3,000-character string, but jumps out immediately once the structure is indented and mismatched nesting becomes visually obvious.
XML, JSON, and YAML all solve the same basic problem — representing structured data as text — but make different tradeoffs. XML uses opening and closing tags (<name>value</name>) and supports attributes, namespaces, mixed content, and formal schemas (DTD or XSD) that can enforce strict validation rules, making it powerful and self-describing but noticeably more verbose than the alternatives. This richer feature set is exactly why XML persists in enterprise systems, SOAP APIs, and document formats where schema validation and namespace disambiguation genuinely matter.
JSON is far more compact than XML and maps naturally onto data structures every programming language already has (objects, arrays, strings, numbers), which is why it became the default for REST APIs and mobile app data — most JSON consumers don't need XML's namespace or mixed-content features and benefit from the smaller payload and simpler parsing. YAML is more human-readable still, using indentation instead of braces or tags and supporting comments (which strict JSON doesn't), making it popular for configuration files like Docker Compose and Kubernetes manifests. In practice, XML wins where formal schemas and document-style mixed content matter, JSON wins for APIs and data interchange, and YAML wins for human-edited configuration.
The vast majority of XML well-formedness errors fall into a handful of predictable categories. Unclosed tags — opening an element like <item> and forgetting the matching </item> — are the single most common mistake, especially in deeply nested documents where it's easy to lose track of how many closing tags you still owe. Mismatched tags, where a closing tag's name doesn't match its corresponding opening tag (like closing <item> with </items>), are a close second, often introduced by find-and-replace edits that only touched one half of a tag pair.
Multiple root elements are another frequent issue: XML requires exactly one top-level element wrapping everything else, so pasting two or more sibling elements at the very top of a document without a common container will fail well-formedness even if every individual tag is otherwise correctly closed. Unescaped special characters inside text content — a bare & instead of &, or an unescaped < inside a value — will also break parsing, since XML reserves &, <, >, ", and ' for markup and requires them to be escaped as entities when they appear literally in text. This tool's validator surfaces the exact structural problem and the tag name involved for each of these cases, so you can jump straight to the fix instead of scanning the whole document by hand.
XML Formatter handles well-formedness checking and pretty-printing. These related developer tools cover other structured-data formats you'll often work with alongside XML.