TextDiff is an online diff tool that allows you to compare two texts and highlights the differences. You can diff the texts by line, word or character. You can diff anything from json files to plain text. Your data is not uploaded to the Internet. Everything is done in your browser.
Just copy and paste your texts into the textareas and see the diffs highlighted. No need to use a desktop application. You can compare files in any format. For example JSON, XML or plain text.