.obj File Extension

What kind of file is a .obj?

An .obj file usually has one of two unrelated meanings:

• A Wavefront OBJ model is a text file describing 3D geometry. Records beginning with v, vt, and vn define positions, texture coordinates, and normals. An f record assembles them into a polygonal face. Materials and texture references commonly live in a separate .mtl file.¹
• A compiled object file contains machine code, symbols, sections, and relocation records for a linker. Microsoft toolchains commonly use .obj for COFF object files, but the exact binary structure depends on the toolchain and target.²

The suffix has no universal magic bytes. A Wavefront model should be readable text with valid OBJ statements. A normal COFF object starts with a machine identifier and section count, not the signatures of a linked Windows image.² Use a format-aware parser rather than guessing from the first few bytes.

IANA does not register an OBJ-specific media type.³ Poly associates the suffix with the deployed, unregistered application/x-executable label for consistent handling, but that label does not prove the file is executable or binary.

How do I open a .obj on my computer?

Open a Wavefront model with Blender, Autodesk Maya, MeshLab, or another 3D editor. Keep any .mtl file and referenced textures beside the model so materials are not lost. OBJ carries basic geometry and materials, but Blender notes that it does not preserve features such as armatures, lights, cameras, parenting, or transformations.⁴

Inspect compiled object code with the tools from its build environment. Microsoft Visual Studio tools understand Windows COFF. llvm-readobj --file-header --sections file.obj can inspect headers and sections across supported object formats without running the code.⁵

Treat an unknown .obj as untrusted. Do not link compiled code into a program until you trust its source, and enable mesh validation when importing an unfamiliar 3D model.

Poly support for .obj

Poly stores, syncs, shares, versions, downloads, and finds .obj files by filename and basic properties. Because the suffix can represent readable 3D geometry or target-specific compiled code, Poly does not provide a format-specific thumbnail, preview, content index, or agent-readable representation.

For visual access, export a 3D asset to a supported preview format. For compiled code, save trusted inspection output as text next to the original. Poly can index the report while preserving the .obj file unchanged.

History of .obj

Wavefront Technologies introduced OBJ for Advanced Visualizer around 1990 and published a specification to support interchange. By the mid-1990s, it was treated as a vendor-neutral way to move surface geometry between 3D applications.¹

Compiler toolchains independently used “object” as the name for relocatable output between compilation and linking. Microsoft adopted .obj for COFF object files. The shared suffix reflects the word “object,” not a relationship between 3D meshes and compiled programs.

Working with .obj and alternatives

For 3D work, choose the destination around what must survive:

Khronos designed glTF for efficient transmission and loading of complete 3D scenes, including meshes, materials, skins, and animations.⁶ Convert a Wavefront model through a 3D application, then verify scale, axes, normals, materials, and texture paths. For compiled .obj files, rebuild from source for the destination platform instead of attempting a format conversion.