XML Linter
Catch the problems that are legal but wrong: inconsistent indentation, unused prefixes, duplicate namespaces, a contradictory declaration.
What is XML Linter?
A linter for XML that parses cleanly but will cause trouble later. Well-formedness is assumed; the findings are about consistency, clarity and portability — the things that make a document hard to review or a namespace bug hard to find.
How it works
The tree is walked recording the indentation of each level, every namespace declaration and its uses, the declared encoding against the actual bytes, and the shape of the prolog. Findings are rule-tagged (lint-indent, lint-bom, lint-namespace, lint-declaration) with a position and an explanation of the consequence, so a warning tells you why it matters rather than just that it exists.
- Paste the document. Drop in XML, a schema, a feed or an XPath expression. Everything is parsed in the page: no upload, no server round trip, and the tools keep working with the network switched off.
- Set the options that match your document. Indent unit, whether to keep comments, which dialect, which output method. The defaults are the safe ones — nothing that changes meaning is enabled for you.
- Read the result, then copy or download it. Results appear as you type, copy straight to the clipboard, and download with a sensible filename (.xml, .xsd, .csv). Reset returns every field to its default.
Examples
A minified document from an API response
Paste one line of XML and the Formatter indents it, wraps long start tags one attribute per line and normalises empty elements — without touching text inside mixed content.
An XPath that works in Chrome and not in your servlet
The XPath Tester evaluates against a real tree and reports the axis or function it cannot support, instead of returning zero nodes and letting you guess why.
A document that will not parse
The Validator gives line and column for every mismatched tag, stray ampersand and duplicate attribute, with the reason in words: which open element was expected, which was found.
A schema that only half matches your data
The XSD Validator marks each violation with the path of the offending node, and the Schema Generator goes the other way — inferring a starting-point XSD from real documents.
Common mistakes
Assuming a pretty-printer cannot change meaning
Whitespace between elements is often insignificant, but inside mixed content it is not: `<p>Hello <b>world</b></p>` must stay on one line. Formatting here re-indents element-only content and leaves mixed content alone.
Treating a validation pass as proof of interoperability
The DTD and XSD validators implement honest subsets. A document reported valid here can still be rejected by a full validator that understands identity constraints, substitution groups or XSD 1.1 assertions — each page lists what it does not cover.
Reading the whole document because the parser did
A DOCTYPE is not inert. If your parser resolves external entities, pasting an untrusted document is enough to read a file or call an internal URL. The XXE Risk Checker shows what a document asks for; the fix is in the parser configuration.
Forgetting that attributes and elements are not interchangeable
`<id>1</id>` and `id="1"` mean different things to every schema and every XPath. When converting to CSV or YAML the distinction is preserved (`@id`), because flattening it away is the change that costs an afternoon later.
Frequently asked questions
Why does mixed indentation matter in a machine-read file?
Because a human reviews it. A file that mixes tabs and spaces lines up differently in every editor, so diffs show noise and review comments land on the wrong line. It also breaks naive text tooling later — which is what the linter exists to prevent.
What is wrong with declaring a namespace I do not use?
Nothing legally, but it is how documents rot: a prefix that nothing references is either leftover from a refactor or a sign that the element after it was meant to use it. The linter reports unused and undeclared prefixes and the Namespace Resolver shows the full mapping.
Can I suppress a rule?
Not individually — the linter is deliberately a fixed checklist, so a clean result means the same thing for everyone. Findings are sorted by severity, and the informational ones can be read as suggestions rather than errors.