How can I tell if a plugin is free to use in my code from github, jquery-plugins.net, etc? Is it all free to use?

In most cases its free to use, as long you dont redistrubute, but of course you have to check all the licenses because it could be diffrent

Indeed, to echo what Sven said, most of all the plugins you will find that are easily downloaded are going to be free and open to use. You can google what the license to the plugin means, and that will help you decide what you can and cannot do with it. But a general rule of thumb is that if it has it's own website for download, or it's easily available on a site like Github, it's very like free and open.

Other sites like codecanyon.com have scripts and plugins, but they very clearly cost money to download.

A beautiful thing about the web community vs other communities like photography, music, etc is that the free and open source network is very strong. It's quite common and encouraged to use, modify, edit, or adapt somebody else's code in general. I mean heck, Github gives you an easy way to fork a repository and do what you want to the code then.

Really, as a designer or developer, it's quite good for your resume and reputation in the web world if you can create an open source plugin that becomes popular and widely used.

Thank you guys!