Download link for Google Spreadsheets CSV export - with Multiple Sheets

Every document in Google Sheets supports the "Chart Tools datasource protocol", which is explained (in a rather haphazard way) in these articles:

1. "Creating a Chart from a Separate Spreadsheet"
2. "Query Language Reference"
3. "Implementing the Chart Tools Datasource Protocol"

To download a specific sheet as a CSV file, replace {key} with the document's ID and {sheet_name} with the name of the sheet to export:

https://docs.google.com/spreadsheets/d/{key}/gviz/tq?tqx=out:csv&sheet={sheet_name}

The datasource protocol is quite flexible. Various other options include:

Response Format: Options include tqx=out:csv (CSV format), tqx=out:html (HTML table), and tqx=out:json (JSON data).

Export part of a sheet: Supply the range={range} option, where the range can be any valid range specifier, e.g. A1:C99 or B2:F.

Execute a SQL query: Supply the tq={query} option, such as tq=SELECT a, b, (d+e)*2 WHERE c < 100 AND x = 'yes'.

Export textual data: Supply the headers=0 option in case your fields contain textual data, otherwise they might be cut out during export.

1. Open your Google sheet
2. Click the "Share" button and configure "Anyone with the link can view"
3. Press F12 to launch debugging tools in your web browser and select the "Net" tab.
4. Select "File -> Download As -> Comma-separated values .csv current sheet" (or whatever format you want, e.g. xlsx, ods, pdf, html, csv, or tsv)
5. Copy the URL of the GET request from the "Net" tab

It will look something like this: https://docs.google.com/spreadsheets/d/KEY/export?format=csv&id=KEY&gid=SHEET_ID

Note, the "gid" parameter is the sheet ID, which you can find at the end of the URL of the open Google sheet. Reference: https://developers.google.com/sheets/api/guides/concepts#sheet_id