I have been playing with n8n for simple stuff, just to test it out, and while there are workarounds, I wanted ultra simple variables so I quickly created and setup a super simple rust API server (GH link) that allows you to:

• create a variable: POST https://simplevar.kifla.dev/var/{OPTIONAL_INITIAL_VALUE}
• get its value: GET https://simplevar.kifla.dev/var/{KEY}
• change its value: PUT https://simplevar.kifla.dev/var/{KEY}/{NEW_VALUE}

The variable is automatically deleted after 10min of create (or last update).

The API is public and does not need any auth. For your variable KEY is automatically created (you can't name it yourself). And that KEY is a UUIDv4 so it's unlikely somebody will find your var.

The vars live only in memory.

You can use my deployment or deploy your own.