Everything is in the title of this post, this script will allow you to decode a base64 string.

Open base64-decode in Script Kit

// Name: Decode Base64
// Description: Decode a base64 string and copy it to the clipboard
// Author: ElTacitos
import "@johnlindquist/kit"
let base64 = await arg("Enter base64 string to decode")
let decoded = atob(base64)
await clipboard.writeText(decoded)
await div(md(`
# ${decoded}
`))