CTX File

What are CTX files and how to open them

Are you having problems opening a CTX 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 CTX files.

What is a CTX file?

CTX files have multiple uses, and Gasteiger Group CTX is one of them. Read more about the other uses further down the page.

Gasteiger Group CTX

Gasteiger Group CTX is a plain text chemical structure file format designed by the research group of Prof. Dr. Johann Gasteiger. It is used to represent small organic molecules (or fragments) in an ASCII, keyword-driven layout. Its main purpose is to allow software tools to read, write, or filter molecular data including atom definitions, bond types, molecular identifiers, and coordinate sets. It is often used within molecular modeling pipelines, notably by the structure generation tool CORINA.

The format is created by chemical structure generators or processors, which emit blocks of keywords followed by molecular data. Common steps include defining a molecule identity, listing atoms with element type and optional charge or labels, specifying bonds between atoms, optionally supplying 2D or 3D coordinates, and possibly describing stereochemistry. After creation, other programs that perform visualization, computation, docking, or QSAR analysis can read these files to reconstruct the molecular topology and geometry.

The identifying structure is entirely ASCII text, arranged using keywords such as IDENT, NAME, MOLECULS, ATOMS, BONDS, BLABEL, 2DCOORD, STEREO, HIGEOM, INTCOORD, and END. Files usually begin with the string /IDENT (that is, ASCII "/IDENT") at byte offset zero; they contain human-readable keywords like MOLECULS, ATOMS, BONDS, ENDBLOCK within their content.

How to open CTX files

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

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

Last updated: September 19, 2026

All known file formats using extension .CTX

While Gasteiger Group CTX is a popular type of CTX-file, we know of 4 different uses of the .CTX file extension. Different software may use files with the same extension for different types of data.

Microsoft Tutorial Course Text

We know that one CTX format is Microsoft Tutorial Course Text. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

Softdisk Text Compressor compressed data

CTX files were created by Softdisk Publishing, a software and internet company that published disk magazines.

These unique compressed text files were never made available to the general public and were used solely for the production of texts for publication.

Sundial Clearlook Document

A Sundial Clearlook Document is the native document format used by the Clearlook word processor developed by Sundial Systems Corporation for OS/2 operating systems. It is used to save richly formatted text documents that include features such as styled text, embedded graphics, headers and footers, tables of contents, footnotes, and layout cells. Documents are composed of independent text or bitmap elements ("cells") that can be layered, resized, positioned, and arranged within pages.

This format is created by Clearlook when users save a document in its own format. Clearlook can read and write its format, and supports importing and exporting other document formats (for example ASCII or WordPerfect) but this format preserves the OS/2-specific layout, styles, and embedded content. It was designed exclusively for 32-bit OS/2, optimized for small size (requiring less than about 3 megabytes of disk space for the application), fast loading, responsive editing, and WYSIWYG viewing at various scales.

Files of this format start with a specific byte signature: the first six bytes at offset zero are 0xCE, 0xCE, 0xF6, 0x00, 0x64, 0x00.

Various apps that use files with this extension

These apps are known to open certain types of CTX files. Remember, different programs may use CTX 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 CTX file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.