One of the unique features of Rebrickable is the Build Engine. Basically - you tell Rebrickable what LEGO sets and parts you own and it will tell you what other LEGO models you can build with them.
Your LEGO collection is the main input to the Build Engine. Rebrickable calculates your total list of owned parts based on your:
- Set Lists
- Part Lists
- Lost Parts
- Assembled Sets
You can indicate which Set Lists/Part Lists can be used in the builds, as there may be some parts you want to keep intact and not used to build other things.
You can choose to Build a Set or MOC or a Custom List.
There are many settings you can change to impact the behaviour of the build.
Color Sensitivity - there are three options for this setting (Exact, Similar, Ignore). They determine how close the color of the source and target parts need to be to consider them a match. If you are on the Pro Plan you can also customise in detail how the colors are matched.
Part Relationships - you can ignore part differences such as Printed/Patterned parts, Mold variations, or Alternate parts which can usually be used as replacements but are not always functionally compatible.
Ignored Parts - you can exclude certain part categories from the build calculations such as Minifig/Minifig Accessories, and non-LEGO parts such as stickers, books, etc.
For more details see Build Settings.
Once the Build Engine finishes its calculations, it will display the parts you need to complete the build.
In addition to the Missing Parts tab, there is a Suggested Sets tab that displays a list of LEGO Sets you can buy that contain the parts you are missing.
There are some parts you may come across in MOCs or Custom Lists that use [No Color/Any Color] as their color. This is a special color used to indicate that it doesn't matter what color the part is. It is meant to be used for parts inside MOCs that can't be seen. The Build Engine takes these into consideration and will match the part accordingly.
LEGO Set inventories have Normal and Spare parts. If you are building a Set, only the Normal parts are required for the build and the Spare parts are ignored. However, spare parts from the sets in your LEGO Collection are included (unless you have specifically excluded them).