Open an LDraw model and see every part it uses, with a link to each part's page, which bricks actually
connect, and anything that looks wrong. Then compare two versions of a build to see what changed.
Private. The checker runs in your browser, so your file never leaves your device.
Files. LDraw .ldr and .mpd models, the format most LEGO building programs can export.
Connections. Worked out for plain bricks, plates and tiles. Other parts are listed and linked, but not connected yet.
First start. Downloads about 7 MB the first time, then works from your browser's cache.
Just looking? To turn a model around in 3D without starting Python, use the LDraw 3D Viewer.
LDraw source
Edits are checked as you type. Units are LDraw units: a stud is 20 apart and a brick is 24 tall.
What the checker found
* The checker cannot work out connections for these parts yet, so they appear as grey boxes.
Expected
Actual
By file order pairs parts by their place in the file, which suits two versions of one file. By position pairs the same part in the same place, for files that list parts in a different order.
The model as structured data
The same model always gives the same text, so two files can be compared by their fingerprint:
Starting Python in your browserInstalling the checkerReadyThe checker could not start in this browser. It needs WebAssembly, which current Chrome, Edge, Firefox and Safari all have.That file is too big for the checker, which handles models up to 5 MB.No problems found: every connection joins real studs that touch and face each other.Looking up part pagesPart links are unavailable right now. Try again in a minute.no catalog pageSame parts, colours, positions and connections.CopiedLoading the parts for the 3D viewThe 3D view could not load here, so the drawing is shown instead.This model is too big to pass to the 3D viewer. Save it as a file and open it there instead.This browser would not pass the model along. Save it as a file and open it in the 3D viewer instead.Step
What the checker looks at
Every part. Each line of the file becomes a part with its colour and position, and parts from submodels are counted too. Parts with a page on this site link straight to it, so you can see which sets include them. When one LDraw number covers several printed or patterned versions, every version is listed.
Connections. Two parts count as connected only where a stud and a socket touch and face each other, so a brick placed a little too high shows up as loose.
Problems. Two copies of a part in the same spot, a stretched or mirrored part, a colour left as "inherit", a line the checker cannot read, and parts it does not know yet.
The 3D view. Turn the model around and step through its build, drawn from LDraw's own part shapes. A part LDraw does not have shows as a plain box.
Old part numbers. LDraw has renamed many parts over the years. The checker follows LDraw's own renames, so older files still find their parts.
Getting an LDraw file
Most LEGO building programs can save or export a model as LDraw, usually as an .ldr file, or as an
.mpd file when the model has submodels. The samples in the checker are small models you can edit to see
how each change shows up.
