Don’t worry. You haven’t found a corrupted file. You’ve found an , and it’s more important than you might think.

When in doubt: Have you run into a mysterious .idx file in a different context? Let us know in the comments below!

You’ve just downloaded a dataset, ripped a DVD, or cloned a GitHub repository, and you notice a file ending in .idx . It won’t open like a normal document, and double-clicking it does… nothing.

In this post, we’ll break down exactly what an .idx file is, the different ways it’s used, and how to open (or rebuild) one. .idx is short for index . An index file is a supporting file that acts like a roadmap or a lookup table. It helps a primary software program or database find specific pieces of information quickly —without scanning an entire huge file.