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How to open .CLD files on Windows

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".

Step-by-step instructions

  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.

Alternative methods

  • Open .CLD in a browser-based viewer if desktop apps fail.
  • Try opening .CLD on Windows with a secondary app to rule out app-specific issues.
  • Convert .CLD only with trusted tools when direct opening is not possible.

Common 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).

Security note

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.

Back to .CLD extension page