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Reviewing Parts FAQ

Like most of this little section of, this page is in development. If you have questions (or answers!) for this page, let us know.

Questions are in bold. Answers are in normal text.

What is "Reviewing Parts"?
After people create new parts for the Part Library, they submit the parts for review. Reviewers check out these submitted parts, finding any problems, and (hopefully) communicating with the part's author to correct any serious defects.

Who can be a reviewer?
There are currently no formal qualifications for being a reviewer. A reviewer should be very comfortable with LDraw, and have a sharp eye for details. Good communication skills are a big plus. :) The core requirement is that you must be ready, willing and able to check part files, reporting problems, and verifying that files are ready for release.

I found a problem with a part file, but I'm not a reviewer. What can I do?
Please, be sure to send in reports about any problems you find in part files! You can send feedback in one of three ways:

  1. Email the part's author.
  2. Post on
  3. Email the part admin.

Do I have to be a part author to be a reviewer?
Short answer: no.
Medium answer: no, but it helps.
Long answer: no, but having more knowledge about writing LDraw part files, and about the guidelines/standard practices of the part library, will tend to increase the value of feedback you give to part authors. And you'll be able to better pin-point problems you find in the parts you review. OTOH, some people make great software testers, but lousy software writers.

How do I become a reviewer?
The same way everything else happens around here: email the parts admin. Send me mail at, and ask if you can be a part reviewer.

How do I post a review?
First, pick the file you want to review. On every part details/tracking history page, you'll find a link for reviewing. Click the link, login if prompted, and make your choice on the certify status. At the moment there are three certify statii available:
No Vote I'm not ready to vote yet. (Clears previous votes!).
This means that you're just leaving a comment. It's also a way you can undo a previous hold or certify vote, without committing to a new vote.
Hold (No) It's getting there, but not yet.
There are errors to be corrected before the part can be released. The author has to take care of the errors.
Certify (Yes) This file is ready for general release.
If you vote for 'Hold' status always make sure that you enter detailed comments about what is wrong with that part. It's the only way the author of the part gets information about what is wrong with the part.


Also see the Review Information page, for another write-up on this topic.

What should I look for when I review a part?
Verify these things in no particular order:

  • Visually check the part very closely. Use a tool such as L3Lab, LDLite, LDGlite, LDView.
  • Make sure the part doesn't crash LEdit.
  • Check the parts default orientation. Compare it to how similar parts are oriented and what orientation of the part would be useful.
  • If the part is a fix to an already official part, ensure that the origin and orientation are unchanged.
  • Check the part with L3P and the -check and -dist options. Make sure no error messages are produced. Reference to the L3P documentation for detailed error description. Contact the author or set a 'Hold' status if you think the errors are of a serious nature.
  • Check the Part for correct BFC (see the 'What is this BFC?' question).


What is this BFC?
Back Face Culling is a way for graphics programs to speed up rendering, by quickly discarding surfaces which are facing away from the viewer. LDraw's core syntax doesn't support BFC operations. With some formatting rules and a few additional meta-statements, part files can support BFC-capable renderers. Encoding part files for BFC is optional. For more information about BFC, see Steve Bliss' BFC page.


How do I check a file for BFC Compliance?
Checking the BCF'ness of a file is generally easy. First, make sure the file has a BFC statement in the header. :) It should look like one of the following lines:


occasionally, you may see one like:


If the file has no BFC statement, or it says 'NOCERTIFY', you can stop checking for BFC'ness.

To check BFC coded files, you have to use the L3Lab program, so grab a copy of it if you don't have it yet.

Open the file in L3Lab and zoom in as necessary. Click the Test | mytest6 menu option. The 'mytest6' option colors all polygons according to their wrapping:


Front side of polygons


Back side of polygons


Unwrapped polygons; this can be caused by unBFC'ed subfiles, or bowtie quads, or by use of the NOCLIP BFC option.

The basic BFC-check is to simply view the file from all angles. If you can see any red, there's a problem.

Of course, there are one or two complications. These are:

  1. There is typically a small amount of 'leaking' at various seams of parts. This is often a problem in the way the part is rendered, and not a problem with the way the part is written.
  2. Primitives and subparts aren't usually complete enclosed objects. So you can generally view the backside of these files. For primitives, this issue can generally be dealt with by knowing which area *should* be the front/outside of the object, and which *should* be the backside. For subparts, the typical approach is to view the part as a whole, and look for problems there.
  3. If the file you are reviewing has an embedded transparent area, you won't be able to check the BFC'ness of any surface viewed *through* the transparent area. You can fall back on viewing the part with mytest6 turned off, and trying to spot areas are incorrectly not drawn. Or you can edit the part file, commenting out lines for the transparent area. Fortunately, current part-authoring standards direct authors to put part components in separate files; these separate files can be individually reviewed for BFC compliance.

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