mac brew install, after brew update, guetzli still not found

[WenchenLi]

brew update
Already up-to-date. brew install guetzli Error: No available formula with the name "guetzli" ==> Searching for similarly named formulae... Error: No similarly named formulae found. ==> Searching taps... Error: No formulae found in taps. ==> You haven't updated Homebrew in a while. A formula for guetzli might have been added recently. Run brew update to get the latest Homebrew updates!