XML Well-Formedness Validator
Paste XML and get parse errors pinned to line numbers, highlighted in a numbered listing of your source. Checks well-formedness - unclosed tags, bad nesting, stray ampersands - not schema conformance. Uses the browser's own DOMParser, so the verdict matches your browser's. Runs fully client-side. Imported Claude artifact. Source: https://github.com/simonw/tools (xml-validator.html, Apache-2.0).
Name your fork
This clones the app's prompt and source into your account as a new unlisted app. You can edit and publish it from your dashboard.
Details
View source prompt + release files — fork-enabled apps share their full source
System prompt (SKILL.md)
---
name: xml-validator
description: Check XML for well-formedness and see the errors pinned to line numbers in the source.
metadata:
tags:
- artifact-import
- dev-tools
source_url: https://tools.simonwillison.net/xml-validator
github_repo_url: https://github.com/simonw/tools
---
# XML Well-Formedness Validator
An imported Claude artifact. Paste XML, click Validate, and any parse error is
reported with its line number and highlighted in a numbered listing of your
source underneath, so you can see exactly where the document breaks.
Note the scope: this is *well-formedness*, not schema validation. It answers
"is this parseable XML" - unclosed tags, bad nesting, stray ampersands,
mismatched quotes - not "does this conform to my XSD". The page opens with a
small valid document already in the box, so you can try it immediately.
It uses the browser's own DOMParser, so the verdict is the same one your
browser would reach. Nothing is uploaded, no model is called, and nothing is
metered.
Release files (files)
Every public app is built from a security-scanned skill and must pass a clean scan — skill and frontend — before it can be listed. Have a skill of your own? Turn it into an app — or read the step-by-step walkthrough.