After the validation and standardization, the compound undergoes structure checker steps, and some of the issues are fixed automatically. The structure checking is performed for both single compounds and multi-component compounds. The list of available structure checkers that can be used can be found here.

A few structure checker examples are:

• Three Dimension Checker:
  The checker searches for 3D (Z) coordinates. Fixer offers: cleaning the structures by 2D clean and set the atomic z-coordinates to zero.

• Rare element checker:
  The checker searches for rare elements in the structures: atoms generally not present in organic compounds (E.g. Ru). No fix is available for this checker.

• Valence error checker:
  Checker searches for valence errors. Fixer offers to remove explicit hydrogens if applicable

• Wiggly bond checker:
  The checker searches for wiggly bond (molecules with unknown or unspecified configuration) starting from chiral centers. The fixer offers to change wiggly bond to single bond.

• Non-stereo wedge bond checker:
  The checker detects wedge bonds which are not connected to chiral centers.The fixer clears the wedge bond.

Some checkers, if present among the Quality checks (e.g. Rare element checker) can be turned on the Submission page in order to register the structure for which the automatic registration was prevented.

Usually a checker-fixer is set for a given source and can be applied during the registration and bulk upload as well.