Check Your VRM Before Your Engine Does

A short checklist for humanoid bones, expressions, textures and skin weights, and how to review all of it in one minute with the VRM Validator.

October 22, 2026 · 4 min read

A VRM file carries a lot of information: a skeleton mapped to humanoid bone names, facial expressions, spring bones for hair and cloth, materials, textures and licence details. When each part is in good shape, the character drops into your game and moves the way you expect. A quick review before import keeps the whole pipeline smooth.

Start with the humanoid map

VRM defines fifteen required bones: hips, spine, head, and the upper leg, lower leg, foot, upper arm, lower arm and hand on each side. Every shared animation clip depends on them. Open the file in the VRM Validator and look at the bone chips. Green chips mean the bone is mapped, and any missing bone is listed by name so you know what to map or rerig.

The validator also checks the order of the hierarchy, so the head sits below the spine and the hand sits below the lower arm. It measures the arm angle in the rest pose too. A T pose gives the cleanest retargeting, and a gentle A pose works well with a small shoulder offset.

Give the face something to drive

Expressions bring a character to life. Blink and the five vowel shapes (aa, ih, ou, ee, oh) are the ones most engines use for blinking and lip sync. The validator lists which presets are present and highlights any expression with no morph target or material bind behind it, since an empty expression has nothing to show.

Look at textures and UVs together

The texture table lists every image with its size, format, memory cost and whether a material uses it. Unused images are easy wins, because removing them shrinks the file without changing how the character looks. Power of two sizes help older devices build mipmaps, and 2048 pixels is a comfortable ceiling for most real time characters.

UV health matters just as much. Healthy atlases that were unwrapped in chart packed islands show a modest share of seam edges. When a remesh step drops the UV map, almost every edge becomes a seam, and the texture appears as a mosaic of shifted patches. The validator measures this and reports it as a finding, so you can rebake the texture before anyone reviews the model. To compare colours against the original model, load both files into the VRM Texture Compare.

Confirm the skin weights

Every skinned vertex needs bone weights that add up to one. The validator counts vertices with no weights, which stay behind when the character moves, and vertices whose weights do not sum to one. Normalising weights is one click in the fixer.

Fix and export

The fixer panel can strip unused textures, compact the binary, normalise weights, fill in empty name, author and licence fields, and resize large textures. Preview the result first and read the before and after size and health score. Downloading the fixed file uses a 30 minute pass, and reports stay free.