GDEX stands for “Good Dictionary EXamples”. It is a system for evaluation of sentences with respect to their suitability to serve as dictionary examples or good examples for teaching purposes.
Sentences are evaluated with respect to their length, use of complicated vocabulary, presence of controversial topics (politics, religion…), sufficient context, refrences pointing outside of the sentence (e.g. pronouns), brand names and other criteria.
The GDEX tool looks at the user-defined number of sentences and sorts them according how well they match the GDEX criteria.