W3cValidate.vim is a plugin that enables buffer/url validation using the http://validator.w3.org api == USAGE == Copy w3cvalidate.vim file inside plugin directory, source it or restart Vim. Use :W3cValidate to validate the current buffer :W3cValidate "[url_here]" to validate a hosted page :W3cValidateDT "[doctype]" to validate the buffer using the [doctype] override. Make sure the doctype is a valid doctype The validator service url can be changed if you run an instance of it localy by setting g:w3_validator_url in .vimrc The script has API timeout default to 20 seconds. You can change it by setting g:w3_apicall_timeout in .vimrc == NOTES == Needs vim compiled with +python option. Works out of the box on Ubuntu and Ubuntu-derivates. Thanks to Yegappan Lakshmanan for Scratch.vim http://www.vim.org/scripts/script.php?script_id=664, I got some ideas for the temporary buffer displaying the errors/warnings from this script.