Instant Source lets you take a look at a web page's source code, to see how things are done. Also, you can edit HTML directly inside Internet Explorer!
While this has always been possible using the IE View Source command, Instant Source changes the concept entirely, and allows you to view the code for the selected elements instantly, without having to open the entire source.
The program integrates into Internet Explorer and opens a new toolbar window which instantly displays the source code for whatever part of the page you select in the browser window.
You can even set it to show source code for every element under your cursor, allowing you to quickly peak through the source as your cursor moves across the page.
Instant Source can show all Flash movies, script files (*.JS, *.VBS), style sheets (*.CSS) and images on a page. You can save all external files into the selected folder with a one click.
Other features include handy HTML, JavaScript and VBScript syntax highlighting and support for viewing external CSS and scripts files directly in the browser.
Why is Internet Explorer's View Source command so inconvenient for viewing HTML?

Because:
Usually, you want to look at the code of a certain part of the page, not the entire page. The time needed to find the right code block may be significant.
You have to select View Source command from the menu and switch to the text editor every time.
You can't access external *.css and *.js files.
The View Source command displays HTML in the Notepad without any syntax highlighting.
The Web Browser (we will talk about Internet Explorer only) does not show the same HTML source as you see! It shows HTML that was loaded from the server without any further processing. However, modern sites extensively use Dynamic HTML for changing the page code after loading. Hence, what-you-see is NOT what-you-get!
Instant Source will resolve these problems. It integrates into Internet Explorer, so you don't need to use an external viewer.

Features:
You get the HTML of the page element as quickly as possible - just hover the mouse over it, or select it.
HTML editing directly inside web browser.
Enhanced View Source command replacement.
Instant Source can display the HTML code that exactly matches the visible content of the page.
It shows all external files on a page and lets you to save them with a one click.