Definition
The Google Sheets API is a RESTful web service that lets your application read, write, and format spreadsheet data over HTTPS. It exposes endpoints to append rows, update cells, create sheets, apply formatting, and run batch operations. To call it, your app authenticates with OAuth 2.0, obtains an access token, and then hits endpoints like spreadsheets.values.append. It is the standard path for desktop and mobile apps that need to treat a Sheet as a database.
The tradeoff is operational complexity. You must store OAuth refresh tokens, handle token expiration, respect per-user and per-project quota limits (currently 300 read or write requests per minute per project), and go through Google's OAuth verification for apps that want production-scale access.
How SheetLinkWP relates to Google Sheets API
Since v1.12.0, SheetLink Forms' default one-click Google Sheets connect writes rows through the Google Sheets API. You click Connect Google, approve a standard consent screen, and pick a spreadsheet with the Google file picker; the plugin then appends each submission via the API under the drive.file scope, so it can only touch the spreadsheets you pick or create - never your whole Drive. There is no Google Cloud project to set up and no API keys to manage: SheetLink's own verified Google app handles the OAuth plumbing, and submission payloads travel directly from your WordPress server to Google, never through SheetLink's servers.
The classic Apps Script method skips the API entirely: you deploy a small web app inside your own Google account and WordPress posts submissions to it. That route avoids OAuth altogether and remains the fully self-hosted alternative.