Last time I checked, Microsoft had nothing like the Sheets API. However, since then, as the sister comment points out, they have published the Graph API (https:

Last time I checked, Microsoft had nothing like the Sheets API. However, since then, as the sister comment points out, they have published the Graph API (https://docs.microsoft.com/en-us/graph/api/overview?toc=./ref/toc.json&view=graph-rest-1.0 https://docs.microsoft.com/en-us/graph/api/overview?toc=./re...), which seems to have a pretty decent set of spreadsheet API methods. Google's spreadsheet API is very powerful, and contrary to the spirit of the OP, I think the update largely preserves existing functionality (the developer may need to adjust their thinking and be aware of other aspects/patterns of Google APIs). I'm actually very glad they came out with v4, as during the lifetime of v3 it was not entirely clear whether they would be updating it further. Offline spreadsheets are completely unusable for most of the use cases that these APIs enable. The biggest value add of the online spreadsheet APIs is to be able to integrate with relevant online data sources to dynamically update the spreadsheet contents, provide typeahead suggestions/autocompletions, or sync data with another system. This can be very powerful because it immediately brings the full power of spreadsheets to the user interface of your data system, without having to build something equivalent to a spreadsheet interface yourself (which, contrary to some loud opinions out there, can be a huge win in business applications by enabling non-technical or partially technical users to be more flexible, more productive, and less dependent on other members of the organization to do their work). Until the graph API, the closest thing to a spreadsheet API provided by a Google competitor was... VBA. Visual Basic for Applications. That is still the main API for desktop Office applications. Good luck using that. I just about gouged my eyes out the last time I tried to use it.