1 Find the set number
It is printed on the box and on the cover of the instructions. Without either, search for the set by name in BrickBack: the catalog covers over 28,000 LEGO® sets, named in your language where available. The instructions are not needed: the set contents come from the catalog.
2 Load its contents
Add the set: BrickBack loads its list of pieces, piece by piece and color by color. The spare pieces included in the box are left out of the count: a set is complete when every piece needed for the build is there.
3 Sort the loose bricks by color
A set's contents are grouped by color. The “Bricks” tab opens “My loose bricks”: tap a piece to change its quantity, sort the list and filter by exact color. The free plan is limited to 30 different pieces in total, counted for life: each combination of piece and color counts once. Deleting a piece does not free a place; adding a previously counted combination again remains free.
“Pieces to buy” gathers the missing pieces from all your sets for free, grouped by set, color or piece type. You can exclude pieces already in your loose bricks.
4 Check off what you have
Every piece you check off brings down the missing count and raises progress. Ten 10% steps fill with the pieces you find, at 10%, 20%, 30%… At 100%, the completed set is framed and dated.
5 Scan the doubtful pieces
Two nearly identical grays, a piece whose exact shape you do not know, a tub where several sets got mixed up: photograph it. BrickBack identifies it and shows which of your sets are missing it; check it off for one of them and its progress goes up. “− 1 +” sets the quantity to check off, up to the number missing.
The scanner is in the middle of “Collection · Bricks · Scan · Ideas · To buy”. “Search for a piece” is there too. Open Settings through ⚙ in Collection. “Cancel” stops identification while you wait; “Try Again” retries the same photo if the service does not respond.
6 Order only what is missing
Whatever is left unchecked is the exact list of pieces to find. BrickBack opens the manufacturer's single-piece shop on that set's pieces. In “To buy”, “Pieces to buy” stays up to date and exports for free to a spreadsheet (CSV) or Rebrickable. Only this list's file exports are free: exporting your collection, wishes or loose bricks remains Pro. Pro adds printing, filtering by set, choosing the order and BrickLink/Brick Owl exports, which you import yourself. Whether a piece is offered in a given color depends on what was produced and what is still in stock. The price and the order are the merchant's.