Scrips in this repository allows you to check status of your webapps in Google Spreadsheets.
In your Google Spreadsheet go to Tools → Scripts Editor and paste content of desired script files.
Then you will be able to use it as regular formulas in your spreadsheet.
For example function HEALTHCHECK_CONTAINS from src/health.gs allows you to check status of given app by performing GET request to URL from the first parameter and verifying that the response contains text given in the second paramter.
In other words, calling =HEALTHCHECK_CONTAINS(A2, "Hello") in your spreadsheet will check if content of a response from URL given in A2 cell contains text "Hello".