.CXF file extension

To open .CXF files on Windows, install or use CAS STN Express (it lists *.cxf as a supported structure file type).

To open a .CXF file, use a chemical-structure application that supports the Chemical eXchange Format (CXF), such as CAS STN Express. If your device can’t open it directly, transfer the file to a desktop system with compatible chemistry software rather than renaming the extension.

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Last updated: April 30, 2026 · Reviewed by Julian Stricker

Open on your device

Choose your operating system for a dedicated step-by-step opening guide.

How to open .CXF files

Use these platform-specific instructions to open .CXF files safely.

Windows

Install or use CAS STN Express (it lists *.cxf as a supported structure file type).
In File Explorer, right-click the .CXF file → Open with → choose STN Express (or the chemistry app you use for structures).
If it still won’t open, confirm with the sender that it is a Chemical eXchange Format file (not an unrelated format that also uses .cxf).

Full Windows guide

Mac

If you have a chemistry application that explicitly supports Chemical eXchange Format (.cxf), open the app first and use its File → Open/Import function.
If double-clicking doesn’t work, Control-click the file → Open With → select your chemistry app (if installed).
If you don’t have compatible macOS software available, transfer the file to a Windows system running STN Express.

Full Mac guide

Linux

Try opening the file from your file manager with an installed chemistry tool that supports Chemical eXchange Format (.cxf) (if available in your workflow).
If your desktop environment only recognizes it as chemical/x-cxf but no app opens it, transfer it to a system with chemistry software that supports .cxf (for example, STN Express on Windows).

Full Linux guide

iOS

iOS typically won’t have built-in support for Chemical eXchange Format; use the Files app to save the .CXF file, then transfer it to a desktop computer with chemistry software (such as STN Express) to open it.

Full iOS guide

Android

Android typically won’t have built-in support for Chemical eXchange Format; download/save the .CXF file, then transfer it to a desktop computer with chemistry software (such as STN Express) to open it.

Full Android guide

Security notes

Treat .CXF as untrusted input when it comes from unknown sources: while it is a data format, any complex parser can have vulnerabilities, so prefer opening it in well-maintained, up-to-date chemistry software.
Be cautious with unexpected .CXF files received by email or download links; if the sender cannot explain what the chemical content is or where it came from, do not open it.
If you are in a regulated or sensitive environment, open CXF files only on systems intended for scientific file processing and avoid uploading confidential chemical data to unknown third-party conversion services.

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Can't open this file?

These are the most common causes and fixes when .CXF files fail to open.

Common reasons

The .CXF file won’t open or shows “unknown format”
File opens, but the structure/data looks incomplete or corrupted
Your system identifies it as chemical/x-cxf, but there is no application to open it

Fix steps

Open the file from within a chemistry tool that supports CXF (for example, CAS STN Express is documented to open *.cxf).
Confirm the file is actually Chemical eXchange Format (CXF); the .cxf extension may be used by other, unrelated formats in some environments.
Ask the sender to export to another widely supported chemical format if your software cannot import CXF.

OS-specific troubleshooting

What is a .CXF file?

.CXF usually refers to the Chemical eXchange Format developed by CAS as an open definition for chemical information exchange. It has been described in standards/interoperability contexts as using ASN.1 with BER encoding. The associated (non-IANA-registered) MIME type commonly seen in desktop MIME databases is chemical/x-cxf.

Background

CXF (Chemical eXchange Format) is a chemistry-focused data exchange format associated with CAS, intended to help move chemical structure information between systems. References describe it as an open definition and note ASN.1/BER encoding, which is typical of structured binary interchange formats.

In practice, you’ll most often encounter .cxf in chemical and scientific workflows where structures and related data need to be saved, shared, or imported into databases and search tools. CAS documentation indicates that STN Express can open structure files including *.cxf.

On many general-purpose systems, .cxf won’t open by default because it is a specialized scientific format. Some desktop environments may still recognize it by a chemical MIME mapping (chemical/x-cxf), but you generally need chemistry software to view or edit the contents meaningfully.

Common MIME types: chemical/x-cxf

Common .CXF issues

The .CXF file won’t open or shows “unknown format”

Most systems don’t include a default viewer for specialized chemical exchange formats, and some apps only support certain chemical formats or subsets.

Open the file from within a chemistry tool that supports CXF (for example, CAS STN Express is documented to open *.cxf).
Confirm the file is actually Chemical eXchange Format (CXF); the .cxf extension may be used by other, unrelated formats in some environments.
Ask the sender to export to another widely supported chemical format if your software cannot import CXF.

File opens, but the structure/data looks incomplete or corrupted

The file may be truncated, damaged in transfer, or not fully supported by the specific importer/version you are using.

Re-download or re-transfer the file (avoid copy/paste through messaging apps that may alter attachments).
Try opening/importing in the originating workflow tool (or in STN Express, which explicitly supports *.cxf).
If possible, ask for a fresh export from the source system.

Your system identifies it as chemical/x-cxf, but there is no application to open it

Some Linux/desktop MIME databases include chemical/x-cxf mappings, but that does not guarantee an installed viewer/editor.

Check your installed chemistry software for an Import/Open option that mentions CXF.
If no compatible Linux/macOS application is available in your environment, use a Windows system with STN Express (per CAS documentation).

FAQ

What is a .CXF file most commonly used for?

Most commonly, .CXF is a Chemical eXchange Format file used to exchange chemical structure information and related data between cheminformatics systems.

What software can open .CXF files?

CAS documentation states that STN Express can open structure files including *.cxf (Chemical Exchange Format). Other chemistry tools may support CXF, but you should verify support in the specific application you use.

Is chemical/x-cxf an official IANA-registered MIME type?

It appears in desktop MIME databases and references (chemical/x-cxf), but you should verify registration status in the IANA Media Types registry; do not assume it is officially registered just because it is recognized on some systems.

Can I convert a file to .CXF by renaming the extension?

No. Renaming only changes the filename; it does not convert the underlying chemical data format. Use an export or conversion feature in chemistry software that supports CXF.

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