Here's the link the tool: chartool
The core idea here is to make it fast and easy to see all the characters in a string along with their associated index within a string. It also lets you directly select a desired substring and see what indices the selection corresponds to.
To start using it just paste or type in whatever text you want to work with. This will result in a series of characters appearing below with each character indicating its index above it. By default the index starts at 0, but this can be adjusted to any index by editing the start index variable.
Once you've entered text and the characters have been displayed you can click and drag along the characters to select a subset that you want to extract. The starting and ending indices are displayed and update as you drag along the characters. You can copy the selected text by either clicking the copy text button or by using any of the typical copy keyboard shortcuts(ctrl + C or command + C).
Hidden characters that aren't normally directly visible will show up in the character display and are shown with a light blue background. The below example shows how tab and newline characters are displayed.
