I paste the context, wait, and find out it was too long.
What you do now
Send it and see. If it overflows, cut something at random and send it again.
What happens instead
The token cost per file, before you attach anything.
What it costs you
No figure for this one. It buys back attention rather than seconds, and a number invented for it would make the other twenty-four less believable.
How to do it
Free, MIT, and it never expires. Nothing on this site is behind a paywall.
Download the appFree and MIT. Or
brew install avaluev/tap/chute