Validation
Nu HTML Checker
Validate HTML documents and inspect markup errors using the W3C Nu checker.
validator.w3.org THE WEB, WELL BOOKMARKED
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98 references, libraries and tools for designing, building and testing the web.
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Validation
W3C CSS Validator
Check stylesheets for syntax and conformance issues, taking the chosen CSS profile into account.
jigsaw.w3.orgValidation
Schema Markup Validator
Inspect structured data and schema.org markup embedded in a page or pasted as code.
validator.schema.orgValidation
Rich Results Test
Check which supported Google rich-result types can be detected in a page’s structured data.
search.google.comValidation
JSONLint
Validate and format JSON documents to find syntax errors in configuration and data.
jsonlint.com