HTML Formatter Validator

The HTML Formatter Validator processes input HTML to produce clean, readable, and standards-compliant markup. It formats code for readability and enforces structural norms aligned with HTML5. The tool helps reduce cognitive load during code reviews and lowers the risk of rendering discrepancies across browsers and email clients. It is aimed at web developers, QA engineers, content teams, CMS publishers, and build engineers who routinely generate, edit, or validate HTML snippets. By providing deterministic output, it reduces churn when updating templates and components. It also serves as an auditing aid for teams migrating legacy markup to modern standards.
Conceptually, the tool parses HTML into a document model and uses a streaming parser to detect syntactic issues. It applies deterministic reflow rules for indentation, line breaks, and attribute ordering. It then serializes the document back to text, preserving content within pre, script, and style blocks. Diagnostics accompany the formatted HTML to highlight errors, warnings, and potential accessibility concerns. If a user requests, the tool can produce a minified version while retaining validity.
Core features include configurable indentation depth, optional minification, whitespace normalization, and strict validity checks with location metadata (line and column numbers) for errors. It supports both full documents and fragments, enabling use in templates and CMS exports. The formatter is idempotent: running it multiple times yields the same output for the same input. It is designed to fail gracefully by reporting issues without altering well-formed content.
Use cases include preparing emails, templated components, and production-ready pages. Unique value arises from its lightweight parsing approach, precise error localization, and the ability to integrate diagnostic data into CI workflows. Output consists of the formatted HTML and a structured diagnostics object that can feed automated checks.