Here is a list of free websites to annotate webpages.
When you have to add some important notes or highlight a particular line or paragraph on a webpage, you can use any of these websites. All of these webpage annotator websites let you create a free account and use their toolbars to annotate webpages.
Most of these websites provide their bookmarklets to annotate a webpage using any browser. Some websites also come with their Chrome and Firefox add-ons. The next time when you will open the same webpages, you will be able to see all your annotations or access your accounts to see the stored annotations.
Here is the first webpage annotator website in this list, named as Diigo.
Diigo is the best website in this list that lets you add notes to webpages, highlight, as well as bookmark the webpages. It comes at the first position in my recommendation because it lets you add unlimited notes or bookmarks to a webpage. Moreover, the free account lets you do 500 highlights and add webpages to read later list. Four different colors are available to highlight the webpages.
Once you sign up to this website, you will be able to use its bookmarklet, Chrome or Firefox add-on to start the annotation. A toolbar comes with multiple options (highlight, sticky note, bookmark, etc.) to let you annotate the webpages.
Scrible is one of my favorite webpage annotator websites that provides free cloud storage (limited) to store your annotated webpages. You can use different colors to highlight the text on a webpage and also add colorful notes to a particular paragraph.
It also lets you select text and make it bold, underline, italic, and strikethrough. So a couple of good options are available to annotate the webpage(s). Currently, the website is in beta phase but works very well. You can use its bookmarklet or install the browser plugin to annotate the webpages.
AnnotateIt is a simple website but handy enough to insert notes on webpages. You can select the text content and add a note for that text content. Apart from this, it also lets you add tags before saving a note for the selected content. The unique feature is that you can set permission if anyone can view and/or edit the annotation or not.
To use this website for annotating the webpages, you first need to create your free account and add its bookmarklet to your preferred browser. After this, you can activate the bookmarklet to annotate a webpage and set the permissions related to the annotation. A unique URL is generated for each individual annotation. You can give the link to any user and he/she can view it without sign up. However, to create own annotations and to edit your annotations (if permission is granted), others have to create an account.
What I felt is missing in these websites is the need of more tools, like arrow, circle, rectangle, ellipse. Still, the websites are fantastic to add important custom notes and highlighters. All are good, but the first website comes with unlimited notes feature that makes me put it in the first position.