CMXA File

What are CMXA files and how to open them

Are you having problems opening a CMXA 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 CMXA files.

What is a CMXA file?

A .CMXA file is an OCaml Bytecode (native Library) file.

OCaml Bytecode (native Library) files are libraries of precompiled OCaml modules in native code. They are built when OCaml source modules (.ml) are compiled to .cmx object files with the native-code compiler ocamlopt, then grouped together into a library for later linking. They provide faster execution than bytecode libraries because the code is already compiled to machine-native form.

Such libraries are produced by running ocamlopt with the -a option, which takes .cmx and associated .o files and assembles them into a .cmxa archive plus a corresponding C static library (.a or .lib). During linking this native-library archive is read along with its contained object files to produce a native executable.

Native libraries may include metadata about C dependencies and custom linking options so that when the archive is used, ocamlopt automatically applies necessary C linker flags stored in the library. They also support cross-module inlining optimisations, which require that .cmx files for referenced modules are available during compilation. Disabling such optimisations is possible via compiler flags (such as -opaque).

Files in this format begin with the byte signature Caml1999Z starting at offset 0.

How to open CMXA files

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

We have not yet verified any programs for Windows that work with this specific file format. If you know one, please use the 'Suggest a program' link below. Thanks!

Last updated: August 31, 2026

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