Print debugging — narrating your code

Every senior developer's secret is embarrassing: they add print statements. Strategic prints turn a black box into a narrated story — and they're the fastest way to find where logic goes wrong.

#The before / after trick

Three prints tell you which step failed:

print("click received from", player.Name)          -- did the event fire?
print("coins before:", coins.Value)                -- what state did we enter?
coins.Value = coins.Value + 10
print("coins after:", coins.Value)                 -- did it change?

• Event never fired? The first print never shows — look at the connection.
• Coins didn't change? The last print matches the middle one — look at the math.
• The gap between two prints is where the bug lives.

#Bisecting with prints

When you don't know where the problem is, don't guess — divide the code in half and print at the middle:

print("A: start")
-- ...setup...
print("B: got the part")    -- half the distance
-- ...handler...
print("C: handler ran")

If "B" shows but "C" doesn't, the bug is between B and C. Narrow again inside that stretch. Each run halves the search — a few runs finds any bug.

#Tracing an event

Prints are how you answer "did the event even fire?" — the first question of every event bug:

clickEvent.OnServerEvent:Connect(function(player)
    print("click from", player.Name)
    -- ...
end)

If nothing prints, the connection never fired — wrong event, wrong name, or the script never connected. If it prints but nothing happens after, the bug is downstream. One line of print told you which half to investigate.

clickEvent.OnServerEvent:Connect(function(player)
-- trace the click
local coins = player.leaderstats.Coins
end)

#Common mistakes

• Removing prints before the bug is fixed. Strip them in a cleanup pass, not during the hunt.
• Printing too little. One print at the end says the end ran — it doesn't say where it broke. Print at the checkpoints.
• Printing after the crash line. A print on the crashing line never runs. Print before the suspicious line.
• Forgetting which side prints come from. Client prints and server prints are separate Output streams in a live game. Watch the right one.

Next: the classic bugs — and how to smell them coming.