NDX File

What are NDX files and how to open them

Are you having problems opening a NDX file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your NDX files.

What is a NDX file?

NDX files have multiple uses, and Chess Assistant Comments Index is one of them. Read more about the other uses further down the page.

Chess Assistant Comments Index

We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

How to open NDX files

Important: Different programs may use files with the NDX file extension for different purposes, so unless you are sure which format your NDX file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested four different NDX openers which you will find listed below.

Last updated: August 10, 2026

All known file formats using extension .NDX

While Chess Assistant Comments Index is a popular type of NDX-file, we know of 3 different uses of the .NDX file extension. Different software may use files with the same extension for different types of data.

DBase Index File

A .NDX file is an index file used by the dBASE database system (specifically legacy versions such as dBASE III and earlier) to make searching and sorting within a related .DBF table much faster. It stores an ordered structure of keys simply pointing into the .DBF file - similar to the index in the back of a book - allowing software like dBASE to locate matching records without scanning every row.

Files of this type are produced by issuing an INDEX ON … TO filename.ndx command in dBASE. Whenever you make changes to the .DBF table (inserting, updating or deleting records), that .NDX file does not update automatically; you must explicitly rebuild or reset it using commands like REINDEX or manually re-create the index. Comparatively newer dBASE formats (such as .MDX) can maintain multiple indexes per table and auto-update them as the table changes.

The technical layout includes a binary B-tree structure built over fixed-size nodes. The header records key attributes such as expression length, type, uniqueness, and pointers to root and total block count. Keys in a leaf node refer back to record numbers in the .DBF table. Index expressions may include field names or expressions up to a set character limit enforced by dBASE.

NDX opener for Windows

We have identified one NDX opener that is compatible with this specific type of NDX file.

WINDEV HFSQL Index

We know that one NDX format is WINDEV HFSQL Index. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

Various apps that use files with this extension

These apps are known to open certain types of NDX files. Remember, different programs may use NDX files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about NDX file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.