There are plenty of desktop screen capture tools around, but most are poor at grabbing web pages. Even if you get a "scrolling window" capture type, it often won't work correctly.
Awesome Screenshot avoids these problems by installing as a Chrome extension, which makes it easy to capture, annotate and share all or any part of just about any web page.
You get options to grab the visible part of a page, the entire page or just a selected area. Captures can be instant, or delayed for a few seconds, perhaps giving you time to access some website feature.
It's also possible to capture your desktop (the entire screen, or a selected application window) or load a local image.
Whatever you choose is opened in a new tab, with a strong set of editing and annotation tools: Crop, Highlight, Blur, freehand drawing, lines, rectangles, ellipses, text captions and more.
There are then options to save the image locally, to Google Drive, to the cloud (and get a shareable link), or simply copy the screenshot and paste it to Gmail, Facebook, Twitter and more.