Validator, developed by Chuck Houpt, brings a desktop W3C markup validator to macOS for private document checking. It runs the W3C validation engine locally so developers can check HTML and XML-based documents without uploading files to external servers, preserving privacy and reducing turnaround time. The app supports drag-and-drop input, bundled source code access, portable execution, and a local web service mode for networked validation. Web developers, designers, and QA testers on Mac benefit from private, offline conformance checks integrated into their local workflows.

Validates the specific XML-based web formats developers actually use

The tool covers HTML and a set of XML document types that commonly appear in modern projects. Supported formats include HTML, XHTML, SVG, MathML, SMIL, and other XML-based documents, so designers working with embedded graphics or mathematical markup can validate the same files they deploy. In practice this means a single validation engine can report conformance for pages that mix HTML and XML fragments without external conversion steps.

Provides networked access for team use through Apache configuration and discovery

Network mode converts the app into a local service by supplying Apache configuration files and Bonjour discovery, enabling other machines on the local network to reach the validator through a browser. That model fits small team labs and offline staging environments where centralizing validation behind an internal URL avoids public uploads. Administrators should expect to edit the supplied Apache config when integrating the service into an existing local web stack.

Exposes its source and targets macOS workflows favored by developers

The app bundles its Xcode project via the AppDNA mechanism, letting developers inspect and recompile the internal code through the Help menu’s Show Source Code option. The developer packages the tool as a portable Mac application that runs without formal installation and documents compatibility across macOS releases including versions noted for Yosemite-era systems. That transparency supports auditability and local modification for specialist toolchains.

Best for privacy-focused Mac web developers, with a note on compatibility

Validator is a practical option for privacy-minded web developers and QA teams who need a local, standards-based checker embedded in Mac workflows; the inclusion of bundled source promotes trust and custom builds. One limitation is the documented compatibility range tied to older macOS releases, which may require testing on more recent desktop environments before adopting it as a team standard.