Then apply the strongest confirmation check: see whether there are files sharing the same base name—if `robot.dx90.vtx` appears alongside `robot.mdl` and `robot.vvd` (and possibly `robot.phy`), that grouping almost always identifies a Source model set, but if the file is just `something.vtx`, lacks `dx90/dx80/sw` patterns, sits outside `models/materials`-style folders, and has no `.mdl/.vvd` companions, all you know is that it’s not a Visio XML file, so the true distinction comes from having both the suffix pattern and the matching Source companions.

This is why most tools load `.VVD` only through the `.MDL`, because the `.MDL` organizes `.VVD` and `.VTX` together and textures (`.VMT`, `.VTF`) prevent the model from showing up gray, so identifying a Source `.VVD` is quickest by spotting same-name companion files like `name.mdl`, `name. If you beloved this post and you would like to acquire additional info concerning VVD file format kindly take a look at our own internet site. vvd`, and `name.dx90.vtx`, noting a `models\…` folder path, checking for the `IDSV` string in a hex viewer, or hitting errors when mismatched with the wrong `.MDL`, and what you can do with it ranges from viewing it with the full asset set to converting via `.MDL`-based decompile workflows or simply verifying it by companion patterns and headers.

In Source Engine terms, a `.VVD` file acts as the vertex payload, meaning it holds the per-vertex information that shapes the mesh and guides lighting and texturing without being a full model alone, containing XYZ positions to define geometry, normals for light response, UVs for texture alignment, and tangent-basis data so normal maps can add detail without raising polygon count.

If the model features animation—anything using bones—the `.VVD` typically stores vertex-weight/bone data, enabling smooth deformation, and it commonly embeds LOD layout metadata plus fixup tables to adjust vertices for lower-detail variants, illustrating its structured runtime design; in total, `.VVD` provides geometry, shading vectors, UVs, and deformation, while `.MDL`/`.VTX` contribute skeleton details, material assignments, batching, and LOD logic for a full in-game model.

A `.VVD` file only represents vertex-level data since it stores things such as positions, normals, UVs, and perhaps bone weights but omits structural context, skeleton bindings, bodygroup logic, and material assignments, all of which the `.MDL` provides as the master file that directs loaders and engines to assemble the complete model.

Meanwhile, the `.VTX` files outline the engine’s draw logic, used for render paths like `dx90`, and without the `.MDL` index and `.VTX` instructions, tools may locate `.VVD` vertex streams but can’t determine correct subsets, mesh boundaries, LOD fixups, or material assignments, leading to incomplete or incorrect results, so most software begins with `.MDL` and lets it call in `.VVD`, `.VTX`, and material files.