En passant is a special pawn capture available immediately after an eligible opposing pawn advances two squares past the capturing pawn.
What to do
Use an otherwise legal position and identify the pawn that just moved. Check whether your pawn could capture it as if it had advanced one square. Make the capture only on the immediately following move.
A mistake to avoid
Do not store the opportunity for later. Also check whether the capture would expose your own king, just as with any other move.
A detail worth checking
Remove the captured pawn from its actual square in the resulting position. This special capture changes two files, which is why checking the final king safety can reveal a line attack that was previously blocked.
Try this practical check
Play a short legal pawn sequence that creates the opportunity, then repeat after inserting another move. Compare why the capture is available in only one version.
Related reading
6 Best Chess Books for Beginners and Improving Players (2026)
