tidy-html5

Validate, correct, and pretty-print HTML/XML documents

brewmacoslinux

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Granddaddy of HTML tools, with support for modern standards

tidy

Validate an HTML file and display errors$ tidy -e input.html

Clean and fix HTML file, save to output$ tidy -m input.html

Convert HTML to XHTML with pretty printing$ tidy -asxhtml -indent input.html