I made these scripts for LFG/PUGs and even to help my teammates track my cooldowns when they don't play with add-ons to do so.
This could be something to integrate directly in the game, similar to what league of legends did: when you press a spell it tells the cooldown in party chat.
It will not say anything when the spell is ready and for 2 sec after you cast it, to avoid spam when you press your cd several times in a row.
The script is the following for Trinket:
/cast Honorable Medallion /run local s,d,_=GetSpellCooldown(195710);local cd=floor(d-GetTime()+s);if(cd>0 and cd<d-2) then cd=cd.."s";SendChatMessage("Trinket "..cd,"PARTY");end
You can personalize it for every spell by changing what's inside the parenthesis of the GetSpellCooldown() function. I suggest you look up the spellID on wowhead, else you can also try by typing the entire name with quotes, e.g. GetSpellCooldown("Cloak of Shadows")
At last, you can also change the content of the announcement if you look at the end of the script: SendChatMessage("Trinket "..cd,"PARTY"). You can replace what's inside the first quotes "Trinket " by anything you want like "CLOAK OF SHADOWS --- ".
Note that it might not work with every spell as some of them have specific interactions, test it before going in arena ! For testing purpose you can replace "PARTY" in the SendChatMessage function at the end of script by "SAY", else you'll need to be grouped.