XML Formatter & Validator

XML (eXtensible Markup Language) is a text-based markup language for storing and transporting structured data. Standardized by the W3C in 1998, it was designed to be both human-readable and machine-readable, and to be completely independent of any platform, language or vendor. Unlike HTML — which has a fixed vocabulary of tags like <p> and <div> — XML lets you invent your own element and attribute names to describe exactly the data you are modeling.

An XML document is built from elements (delimited by start and end tags), attributes (name/value pairs on a start tag), text content, comments, CDATA sections and an optional declaration such as <?xml version="1.0" encoding="UTF-8"?>. Every well-formed document has exactly one root element that contains everything else, forming a strict tree. Because that tree maps naturally onto hierarchical data, XML became the backbone of countless formats and protocols: SOAP web services, RSS and Atom feeds, SVG vector graphics, Office Open XML (DOCX, XLSX), Android layouts, Maven and Spring configuration, sitemaps and much more.

XML formatting — also called beautifying or pretty-printing— is the process of adding consistent indentation and line breaks so the document's hierarchy is visually obvious. Machine- generated XML is frequently emitted as one long line to save bytes, which makes it nearly impossible to read. A formatter parses that XML into a tree and re-serializes it with the indentation you choose, so nested elements line up cleanly and you can scan the structure at a glance.

Under the hood, an XML beautifier performs a two-step dance: parse, then serialize. First the raw text is fed into an XML parser, which walks the characters and builds an in-memory tree of elements, attributes, text and other nodes — reporting an error the instant the syntax breaks the rules. Once that tree exists, the serializer writes it back out, increasing the indentation level each time it descends into a child element and decreasing it on the way out.

Good pretty-printing is more nuanced than simply adding tabs. A quality formatter keeps a short element with a single text child on one line (<title>Hello</title>) for readability, but expands elements that contain child elements onto separate lines. It preserves CDATA sections and comments verbatim, keeps attribute order stable so diffs stay clean, and collapses the meaningless whitespace between tags while protecting significant whitespace inside text. This tool lets you choose 2 spaces, 4 spaces, tabs or a custom indent width, and because every step runs locally in your browser, your data never leaves your device.

Minification is the inverse operation: the formatter drops the whitespace-only text nodes that exist purely for layout, producing the smallest possible document for transport or storage. The tool reports the original size, the minified size and the exact percentage saved so you can quantify the win.

XML defines two distinct levels of correctness, and it is important to understand the difference. A document is well-formed when it obeys XML's core syntax rules; it is validwhen, in addition, it conforms to a schema (a DTD or XSD) that defines the allowed structure.

For a document to be well-formed it must satisfy rules such as:

• There is exactly one root element wrapping all other content.
• Every start tag has a matching end tag, or is a self-closing empty element (<br/>).
• Elements are properly nested — they may not overlap.
• All attribute values are wrapped in matching single or double quotes.
• The reserved characters < and & are escaped in text as < and &.
• Element and attribute names are case-sensitive and follow XML naming rules.

This tool's validator checks well-formedness in real time and goes beyond a simple pass/fail:

• Exact line and column — jump straight to the first error instead of scanning hundreds of lines.
• Plain-English explanations — understand why the document is invalid, not just that it is.
• Suggested fixes — get an actionable recommendation for each error.
• Notes — non-fatal observations like a missing declaration or multiple root elements are surfaced too.

For schema-level validation, you can generate a starter XSD from a representative sample and use it as the contract that future documents must satisfy — catching breaking changes long before they reach production.

JSON overtook XML as the default format for web APIs, but the two coexist for good reasons. Both represent hierarchical data; they differ in verbosity, capability and ergonomics.

Choose JSON for lightweight, high-throughput web and mobile APIs where payload size and parsing speed dominate. Choose XML when you need attributes, namespaces, mixed content, comments or rich schema validation — document formats, enterprise messaging, financial standards and configuration files. When you need to move between the two, this tool converts XML to JSON (and back) in a single click.

1. Always declare encoding. Start documents with <?xml version="1.0" encoding="UTF-8"?> so parsers interpret bytes correctly.
2. Use elements for data, attributes for metadata. Put the core data in child elements and reserve attributes for identifiers, flags and units that describe that data.
3. Pick one naming convention and stick to it. Whether camelCase, PascalCase or kebab-case, consistency makes documents predictable and tooling-friendly.
4. Escape reserved characters. Replace <, > and & with entities, or wrap free-form text in a CDATA section.
5. Keep one root element. A well-formed document has exactly one top-level element; wrap collections in a container.
6. Define a schema for contracts. Use an XSD to document and enforce the structure other systems depend on, and validate incoming documents against it.
7. Use namespaces to avoid collisions. When mixing vocabularies, qualify elements with a namespace prefix so names never clash.
8. Minify in production, beautify in development. Ship the smallest payload to consumers, but keep a formatted copy for debugging.

The overwhelming majority of "not well-formed" problems fall into a handful of recurring categories:

Our validator detects each of these and reports the exact location, while the Auto-fix button repairs the most common ones — escaping bare ampersands and normalizing smart quotes — in a single click.

As documents combine vocabularies from different sources, two elements can easily end up with the same name but different meanings — a <table> of furniture versus an HTML <table>. XML namespaces solve this by qualifying names with a unique URI, so the parser can tell them apart.

A namespace is declared with an xmlns attribute, usually bound to a short prefix: xmlns:h="http://www.w3.org/TR/html4/". An element written as <h:table>then belongs to that namespace. A default namespace (xmlns="…" with no prefix) applies to an element and its unprefixed descendants. The URI is an identifier, not a location — the parser never fetches it. Our analyzer counts and lists every namespace your document declares so you can audit them at a glance.

A schema is a formal description of what a class of XML documents is allowed to contain. It turns an informal agreement ("every order has a customer and one or more line items") into a machine-checkable contract. There are several schema languages:

• DTD (Document Type Definition) — the original, compact schema language. It defines elements, attributes and entities but has no data-type system and isn't itself written in XML.
• XSD (XML Schema Definition) — the W3C standard and the most widely used today. It is written in XML, supports rich data types (integer, date, decimal, custom restrictions), and expresses cardinality with minOccurs and maxOccurs.
• RELAX NG — a simpler, expressive alternative popular in document publishing.

Schema validation checks that a well-formed document also matches its schema: the right elements appear in the right order, attributes have valid types, and required fields are present. This tool can generate a starter XSD directly from a sample document — inferring element occurrence and simple types — giving you a contract you can refine and reuse to validate future data.

XPath (XML Path Language) is a query language for selecting nodes in an XML document, much like a file-system path selects files. It is the foundation of XSLT transformations, XQuery and many libraries that extract data from XML.

A few of the most common patterns:

• /catalog/book — every book that is a direct child of the root catalog.
• //title — every title element anywhere in the document.
• /catalog/book[2] — the second book (XPath indexes are 1-based).
• //book/@id — the id attribute of every book.
• //book/title/text() — the text content of each book title.

Our XPath explorer evaluates expressions against your document in real time and lists the matching nodes, and the tree viewer generates the absolute XPath of any node you select so you can copy it straight into your XSLT, code or test assertions.

XML remains central to enterprise integration — SOAP services, financial messaging (ISO 20022, FIXML), healthcare (HL7), publishing and government data all rely on it. Good tooling pays for itself many times over. Here is a practical workflow this toolkit supports end to end:

1. Inspect the payload. Paste a response or fetch it from a URL or feed, then format it to understand the shape of the data.
2. Validate well-formedness. Confirm the document parses cleanly before you build against it.
3. Explore and query. Use the tree viewer and XPath explorer to locate the exact nodes you need.
4. Generate models. Produce TypeScript, Python, Go, C#, Java or GraphQL types so your client code is type-safe from day one.
5. Lock in a schema. Generate an XSD to document the contract and validate future payloads against it.
6. Convert when needed. Transform XML to JSON, CSV or YAML to feed downstream systems, or convert JSON back into XML.
7. Diff for breaking changes. Compare old and new payloads to spot added, removed or changed nodes instantly.

Because everything runs client-side — and the parser never resolves external entities or fetches DTDs — you can safely paste internal endpoints, tokens and sensitive payloads. Nothing is transmitted to a server, which also structurally protects you against XXE attacks.