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.CLD file extension

To open .CLD files on Windows, identify the type: open the file in a text editor (Notepad) to see if it looks like readable command-definition text; if not, check the first bytes in a hex viewer for the magic number "ICLD".

To open a .CLD file, first identify whether it’s an OpenVMS DCL command definition (text-based, used with CDU/SET COMMAND) or an Illuscio volumetric imaging CLD file (binary, magic number "ICLD"). On most modern desktops you can at least inspect the file (text editor or hex viewer), but full use typically requires OpenVMS tools or software that understands model/vnd.cld.

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Last updated: April 29, 2026 · Reviewed by Julian Stricker

Open on your device

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

How to open .CLD files

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

Windows

  1. Identify the type: open the file in a text editor (Notepad) to see if it looks like readable command-definition text; if not, check the first bytes in a hex viewer for the magic number "ICLD".
  2. If it’s readable command-definition text, you can inspect it on Windows, but to actually compile/use it you generally need an OpenVMS environment/tools (CDU/SET COMMAND).
  3. If it’s an "ICLD" binary file (model/vnd.cld), you will need software specifically designed to read model/vnd.cld; otherwise you can only inspect it with a hex viewer.
Full Windows guide

Mac

  1. Identify the type: open the file with a text editor to see if it’s readable (OpenVMS command definition) or use a hex viewer to check for the "ICLD" magic number.
  2. For OpenVMS command definition .CLD files, macOS can view/edit as text, but processing them typically requires OpenVMS utilities (CDU/SET COMMAND) on an OpenVMS system.
  3. For model/vnd.cld files, use software that explicitly supports Illuscio CLD; otherwise treat it as binary data and do not expect preview support.
Full Mac guide

Linux

  1. Identify the type: try viewing it with a text viewer (e.g., less) and, if it’s not readable, check the header bytes for "ICLD" using a hex tool.
  2. If it’s an OpenVMS command definition file, Linux can edit it as text, but compiling/using it typically requires an OpenVMS environment with CDU/SET COMMAND.
  3. If it’s a model/vnd.cld file, use an application that supports model/vnd.cld; otherwise you can only inspect the raw data.
Full Linux guide

iOS

  1. iOS generally won’t have native support for either CLD type; use Files to share the .CLD to a desktop for inspection, or to a specialized app only if it explicitly states support for model/vnd.cld.
Full iOS guide

Android

  1. Android generally won’t have native support for either CLD type; use a file manager to transfer the .CLD to a desktop/OpenVMS system, or open it only for basic inspection (text/hex) if you have a suitable viewer.
Full Android guide

Security notes

  • Treat unknown .CLD files as potentially untrusted input: both text-based command definitions and binary model/vnd.cld files rely on parsers/tools that could have vulnerabilities if fed malformed data.
  • If the .CLD is an OpenVMS command definition file, applying it (via SET COMMAND/CDU on an OpenVMS system) can change command behavior; review the content before loading it in a privileged or production environment.
  • If the .CLD is a model/vnd.cld file (magic "ICLD"), prefer opening it only in software that explicitly supports model/vnd.cld and comes from a trusted source, since it is a specialized binary format.

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Can't open this file?

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

Common reasons

  • The .CLD file opens as gibberish or won’t display as text
  • You can view the .CLD file, but you can’t 'run' it
  • Wrong application association after double-clicking

Fix steps

  1. Check the first bytes for the magic number "ICLD" to confirm a model/vnd.cld file.
  2. If it should be a command-definition file, re-transfer it using a method that preserves text correctly (and verify the file isn’t truncated).
  3. If it is model/vnd.cld, use software that explicitly supports model/vnd.cld rather than a text editor.

OS-specific troubleshooting

What is a .CLD file?

.CLD is an ambiguous extension. In OpenVMS, .CLD is the default file type for a command definition file that defines DCL commands and is processed by the Command Definition Utility (CDU) and related tools (e.g., SET COMMAND). Separately, IANA registers model/vnd.cld for Illuscio volumetric imaging point data/metadata, with file extension .cld and magic number "ICLD".

Background

In OpenVMS environments, .CLD files are central to defining how DCL commands behave. They describe command syntax and options, and they are compiled/processed by OpenVMS utilities (CDU and SET COMMAND) to make commands available to users. If you received a .CLD file from an OpenVMS system (or in the context of VMS/DCL tooling), it is most likely this command-definition type.

Independently, .CLD is also used for Illuscio volumetric imaging point data/metadata, formally registered with IANA as media type model/vnd.cld. These .CLD files are expected to be binary and can be recognized by the magic number "ICLD".

Because these uses are unrelated, the practical “how to open” answer depends on your source: OpenVMS/DCL workflows vs. volumetric imaging workflows. When in doubt, check whether the file starts with readable text (typical for DCL command definitions) or begins with the "ICLD" signature (typical for model/vnd.cld).

Common MIME types: model/vnd.cld

Further reading

Authoritative resources for more details on the .CLD format.

Common .CLD issues

The .CLD file opens as gibberish or won’t display as text

Many .CLD files (model/vnd.cld) are binary. If you expected an OpenVMS command definition file but see unreadable characters, you may have the Illuscio "ICLD" format or a corrupted transfer.

  1. Check the first bytes for the magic number "ICLD" to confirm a model/vnd.cld file.
  2. If it should be a command-definition file, re-transfer it using a method that preserves text correctly (and verify the file isn’t truncated).
  3. If it is model/vnd.cld, use software that explicitly supports model/vnd.cld rather than a text editor.

You can view the .CLD file, but you can’t 'run' it

An OpenVMS .CLD file is a command definition source file; it must be processed by OpenVMS tools (CDU/SET COMMAND) to define commands, not executed like a program.

  1. Open and review the file as text to confirm it is a DCL command definition.
  2. Use an OpenVMS environment and the documented command-definition utilities (CDU/SET COMMAND) to compile/activate the definitions.

Wrong application association after double-clicking

Because .CLD is ambiguous and uncommon on modern desktops, the OS may associate it with an incorrect app or no app at all.

  1. Open it explicitly with a text editor (to check if it’s a DCL definition) or a hex viewer (to check for "ICLD").
  2. Avoid renaming the extension to force an app; instead, select the correct workflow (OpenVMS tools vs. model/vnd.cld-capable software).

FAQ

How can I tell which kind of .CLD file I have?

Check the file header and context. If the file starts with the magic number "ICLD", it matches the IANA-registered model/vnd.cld format. If it is readable text and came from an OpenVMS/DCL context, it is likely an OpenVMS command definition (.CLD) file.

What program opens OpenVMS .CLD command definition files?

You can view/edit them in any text editor, but to actually process them you typically use OpenVMS command definition utilities (CDU and related SET COMMAND processing) on an OpenVMS system.

Is there an official MIME type for .CLD?

Yes for the Illuscio volumetric imaging format: IANA registers model/vnd.cld with file extension .cld and magic number "ICLD". The OpenVMS command definition use is a different meaning of the .CLD extension.

Can I convert a .CLD file by renaming the extension?

No. Renaming does not change the underlying format. First identify whether it is an OpenVMS command definition file or a model/vnd.cld binary file, then use the appropriate tools/workflow for that type.

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