Texel

Texel

Texel is a format and a toolchain for making Minecraft textures as code. A texture is a JSON spec: a palette and an ordered list of drawing operations addressed to named parts and faces of the model (head.front, rightArm.sides@overlay). A compiler turns the spec into the PNG the game reads, the same bytes every time, and a review returns what is wrong with it as JSON paths, fix hints, an art score and pixel-art advice. The tools are built for AI agents: an MCP server, a command-line tool and an Agent Skill, also packaged as a Claude Code plugin.

It covers player skins (classic and slim) and, through layouts, 68 other textures, all in the Java Edition 1.21 texture layouts: 57 mob textures (zombies, skeletons, creepers, horses, llamas, foxes, bees, axolotls, illagers, wardens, golems and more), armor layers, capes with elytra, items, blocks with their top and side files (logs, grass, furnaces), plants, GUI sprites, particles and paintings. Textures can animate and glow, and a set of specs builds a resource pack that Texel also checks.

Texel is open source (MIT) and in development, at version 0.9.0. The format is versioned (version: 1) but may still change between minor releases. Treat everything as a beta. The site texel.dev.br is built on this toolchain.

The image above is the review sheet the tools return for this spec. It is the wizard example without its $schema, description, author and tags fields and the layers' note comments, which do not change the pixels (both compile to the same PNG):

{
  "version": 1,
  "name": "Star Wizard",
  "model": "classic",
  "palette": {
    "skin": "#e0ac7e", "robe": "#2f4fb0", "gold": "#e8c34a", "beard": "#dcdcdc",
    "eyes": "#3a6fd9", "boots": "#4a3324", "star": "#fff1a8"
  },
  "layers": [
    { "op": "material", "target": "all", "color": "skin", "kind": "skin" },
    { "op": "material", "target": "body+arms", "color": "robe", "kind": "fabric" },
    { "op": "material", "target": "legs", "color": "robe~-1", "kind": "fabric" },
    { "op": "material", "target": "arms", "region": "hands", "color": "skin", "kind": "skin" },
    { "op": "rect", "target": "arms.sides", "region": "cuffs", "color": "gold" },
    { "op": "material", "target": "legs", "region": "boots", "color": "boots", "kind": "leather" },
    { "op": "face", "id": "face", "skin": "skin", "eyes": "eyes", "brows": "beard", "beard": "full", "beardColor": "beard", "mouth": "smile" },
    { "op": "hair", "id": "hair", "color": "beard", "style": "long", "fringe": "parted" },
    { "op": "lighting" },
    { "op": "rect", "target": "body.sides", "region": "belt", "color": "gold" },
    { "op": "points", "target": "body.front", "points": [[3, 8], [4, 8]], "color": "gold~-2" },
    { "op": "points", "target": "body.front+back", "points": [[1, 2], [6, 4], [2, 6], [5, 10]], "color": "star" },
    { "op": "points", "target": "legs.front", "points": [[1, 1], [2, 4]], "color": "star" },
    { "op": "material", "id": "hood", "target": "body.back@overlay", "y": 0, "h": 3, "color": "robe~-1", "kind": "fabric" },
    { "op": "rect", "target": "body.front@overlay", "region": "collar", "color": "gold~-1" },
    { "op": "rect", "target": "arms.sides@overlay", "region": "cuffs", "color": "gold~1" }
  ]
}

The 64 × 64 texture it compiles to is docs/images/wizard.png.

Installing

The MCP server and the CLI need Node 20 or later.

Claude Code plugin. This repository is a plugin marketplace. The plugin starts the MCP server from a single bundled file (no npm install) and adds the minecraft-skin-design skill. Files are written to the project directory.

/plugin marketplace add Brunovncs/texel-mcp
/plugin install texel@texel

Or use this prompt. Paste it into the agent you want to use Texel with (Claude Code, Codex, Cursor, Claude Desktop or any other client with MCP support) and it installs the MCP server for you:

Install the Texel MCP server for me (https://github.com/Brunovncs/texel-mcp).

1. Check that Node.js 20 or later is installed (`node --version`). If it is not, stop and tell me.
2. Create the folder ~/.texel (%USERPROFILE%\.texel on Windows) and download the single-file
   server into it:
   https://raw.githubusercontent.com/Brunovncs/texel-mcp/main/plugin/server/texel-mcp.mjs
3. Check that it runs: `node <path to texel-mcp.mjs> --version` must print a version number.
4. Ask me which folder the skins should be saved in. If I don't care, skip the --workspace part
   below; files then go to the directory the client starts the server in.
5. Register it as an MCP server named "texel" in the client you are running in, using absolute
   paths:
   - Claude Code: claude mcp add --scope user texel -- node <path to texel-mcp.mjs> --workspace <folder>
   - Any other client: add this to its MCP configuration, keeping the servers already there:
     {"mcpServers": {"texel": {"command": "node",
       "args": ["<path to texel-mcp.mjs>", "--workspace", "<folder>"]}}}
6. Tell me what you changed and whether I need to restart the client. Once the tools are
   available, call texel_get_example and then texel_render on that example to confirm they work.

Any MCP client. The package is texel-mcp on npm. This configuration works in Claude Desktop, Cursor, VS Code and other clients that read the usual mcpServers format:

{
  "mcpServers": {
    "texel": {
      "command": "npx",
      "args": ["-y", "texel-mcp", "--workspace", "/absolute/path/skins"]
    }
  }
}

In Claude Code the same is claude mcp add texel -- npx -y texel-mcp. To run a local build instead (see Building and testing), point the client at the file: "command": "node", "args": ["/absolute/path/texel-mcp/dist/texel-mcp.mjs", "--workspace", "/absolute/path/skins"]. plugin/server/texel-mcp.mjs is the same server with its dependencies bundled, and runs from anywhere with plain node.

CLI. npx -y -p texel-mcp texel-cli build skin.json -o skin.png --sheet sheet.png, or node dist/texel.mjs ... from a build. It has no dependencies. --help lists the commands: build, review, patch, sheet, palette, family, import, diff, pack, check-pack, share, pull, live, format, layouts and init. Exit codes: 0 done, 1 the spec, family or pack has errors, 2 bad usage.

All writes go to one workspace directory: --workspace, $TEXEL_WORKSPACE, or the directory the server was started in. Paths that resolve outside it are refused. docs/install.md has the details, including installing the skill by hand.

The spec

A spec has a palette (names for colors, with derived tones such as robe~-1, a step darker and cooler), an optional legend (one character per color, for pixel rows) and layers, which run in order. Each layer is one of 18 operations. Twelve are plain drawing (fill, rect, clear, pixels, points, line, gradient, pattern, noise, shade, copy, mirror), one fixes symmetry (symmetrize) and five are higher level: material (fabric, leather, metal, fur, knit and other surfaces), face, hair, lighting and bevel (raised and inset frames in the vanilla GUI style). Any operation marked "emissive": true also paints the texture's glow map, <name>_eyes.png.

A layer's target is a selector: parts, faces and a layer, as in head.front, legs.sides, body.front+back@overlay or arms.top@both. Coordinates are local to each face: (0, 0) is the top-left pixel of the face as seen from outside the model, and drawing is clipped to the face. A selector that matches several faces runs the operation once per face, so { "op": "rect", "target": "legs.sides", "y": -2, "color": "boots" } paints the bottom two rows all the way around both legs. Named regions (belt, cuffs, boots, hands, collar) stand in for row numbers.

Changes are made with patches by layer id ({ "patch": [{ "do": "update", "id": "hair", "set": { "style": "ponytail" } }] }), so a fix round touches only the layers it names. The same patches make animation frames ("animation": { "frames": [{}, { "patch": [...] }] } compiles to a strip and its .png.mcmeta, or one file per frame for particles) and family members: a family expands one base spec into variants or a matrix of axes (teams, ranks, factions) by swapping palettes, turning layers on and off, patching base layers by id and appending layers, so its members can be different characters, not only recolors. An existing PNG can be imported into an editable spec, one layer per painted face, and import --pixelize first turns any picture (concept art, an HD skin) into a texture of the layout's size.

asset says where a texture goes in a resource pack (mobs default to the vanilla file they replace). pack builds the pack from specs and families, with pack.mcmeta for a Minecraft version (1.21 to 1.21.11) and, on request, the models, block states and item definitions a new item or block needs; check-pack checks any pack: its format and versions, file names, PNGs, .mcmeta animations and GUI scaling, entity texture sizes, references to missing models or textures and unused textures.

The full reference is docs/spec.md, with a JSON Schema in schema/skinspec.v1.json. docs/protocol.md describes the loop an agent is expected to follow (brief, draft, render, review, patch, ship), and docs/art-guide.md what makes a skin read well at 64 × 64. The same pages are available to the agent through texel_read_docs and the texel://docs/{page} resources, and the 19 examples in examples/ through texel_get_example.

What the review returns

Every render comes with a review. With a typo in a palette name and in a face name, the relevant part of the answer is:

{
  "ok": false,
  "score": 38,
  "issues": [
    { "level": "error", "code": "bad-color", "path": "$.layers[1].color",
      "message": "unknown color or palette key \"clth\"", "hint": "did you mean \"cloth\"?" },
    { "level": "error", "code": "bad-selector", "path": "$.layers[2].target",
      "message": "unknown face \"frnt\"", "hint": "did you mean \"front\"?" },
    { "level": "warning", "code": "blank-face", "path": "head.front",
      "message": "the face (head.front) uses fewer than 3 colors and will read as blank",
      "hint": "draw eyes, brows and a mouth with a \"pixels\" op on head.front" }
  ]
}

Errors and warnings point at the JSON path or the face that caused them, and most carry a hint that names the fix. Codes are stable across releases and listed with their meaning in docs/spec.md (ISSUE_CODES in code); a test keeps the list equal to what the source can report. Block textures also get their tiling measured: how much harder each edge breaks than the texture's own neighbors where copies meet (stats.seams, tile-seam). The score (0 to 100) only measures technical hygiene: errors, holes in the base layer, blank faces, flat surfaces, too few colors. The art part of the review has its own score from seven measured checks: R2 to R7 (face readability, lightness contrast between parts, light from above, surface texture, a designed back, use of the overlay for depth) and a color count, each with a note on what was measured and a hint. art.advice names classic pixel-art mistakes found in the texture (pillow shading, shadows that only get darker, static-like noise, a band that stops at a cube corner) with the faces where they show; it never changes a score. A next list orders what to fix first.

Whether the texture matches the brief (R1) is never measured. The MCP tools return a review sheet image (front, back, both sides and the texture, as above) so an agent with vision can judge that itself, and a text render for models without vision. The sheet adds what a texture needs: a block tiled 3 × 3 and in 3D, a GUI sprite resized the way the game resizes it, every animation frame, the glowing pixels on black. In clients that support MCP Apps, texel_render also opens an interactive 3D preview.

Tools

The MCP server has 16 tools, resources for the docs, examples and schemas, the ui://texel/viewer MCP App and 5 prompts (design_skin, design_texture, continue_skin, design_family, critique_skin).

How it works

The hard part of drawing a Minecraft texture is not the drawing but the map. A skin's right arm is six rectangles scattered over a 64 × 64 atlas, some mirrored, the overlay layer is a second set of rectangles elsewhere, a pig's body lies on its side so its "top" is the animal's back, and every mob has its own atlas. An agent writing pixels into the atlas directly has to carry that map in its head and gets it wrong in ways it cannot see.

In Texel the compiler owns the map. Each layout is data: its parts as boxes with sizes and UV origins, which parts are mirrored, which lie turned, and which are cut out by transparency. The agent addresses rightArm.front in the face's own coordinates, and the compiler maps every pixel to its place in the atlas. The review, the sheet views, the 3D preview, import and diff read the atlas back through the same map. That turns a spatial task the agent is bad at into a symbolic one it is good at: naming parts, choosing colors, ordering layers, and acting on errors that point at a line of JSON.

Compilation is deterministic. The only randomness is in noise and material, and both use a seeded generator (the seed defaults to the layer's position), so the same spec gives the same PNG, byte for byte. That makes a spec something that can be reviewed in a diff, kept in version control and regenerated in a build.

Every mob layout was checked against the decompiled Java model code (texOffs and addBox) and by running the vanilla textures of 1.21.1, 1.21.5 and 1.21.11 through it: every opaque pixel of the vanilla file must fall on a face, and the views must show the mob. The few pixels a layout leaves out are listed in its note (an easter egg, a stray pixel, a saddle that moved to its own file in 1.21.5).

The code is in src/core (compiler, layouts, review, views, PNG and zip encoding and decoding, resource packs; no dependencies and no DOM), src/mcp (the server and the MCP App viewer), src/cli, and src/live (live sessions and the update check). The MCP server depends on @modelcontextprotocol/server and zod; the CLI has no dependencies.

Measurements

Measured on an AMD Ryzen 5 7600 (12 threads), Windows 11, Node 22.13.1, with npm run measure (scripts/measure.ts): each of the 19 bundled examples was compiled 210 times in one process, the first 10 runs as warm-up, and the table shows the median of the other 200. "Compile + PNG" is the spec text to an encoded PNG. "Full render" is what texel_render computes: compile, the full review with art checks and advice, the review sheet and both PNGs. Spec size is the example file minified with JSON.stringify; PNGs are encoded at zlib level 9, as the tools do. An animated example compiles every frame.

Across the examples the median is 1.66 ms to compile and encode and 16.6 ms for a full render. Startup of the MCP server and the transfer of the sheet image to the client are not included.

A spec is not smaller than the image it produces: the median minified spec is 1.33 times the size of its PNG, between 735 and 3 272 bytes. At a rough 4 bytes per token that is about 180 to 820 tokens per spec; this was not checked with a tokenizer, and JSON usually takes more tokens per byte than prose. The point of the format is not size. A PNG is compressed binary an agent cannot write or edit by hand, while each line of a spec is a decision that can be read, patched and reviewed.

Determinism was checked three ways. Within one process, all 210 runs of each example produced byte-identical PNGs (one distinct SHA-256 per example). A test keeps a hash of every example's texture, so a change in what an existing spec renders fails the suite. For 0.8.0, the CLI built and installed from the packed npm tarball produced the same hashes for the four examples that were compared (explorer, knight, creeper, ember-blade). All of this ran on one Windows machine; the CI workflow runs the same test suite on Linux, but identical bytes across operating systems have not been compared directly.

Other counts at version 0.9.0: 19 example specs and 1 example family (6 members), 69 layouts plus 74 aliases (husk, stray, elytra, mooshroom, vindicator, elder_guardian, log and others), 18 operations, 116 issue codes, and 180 tests in 14 files.

Limitations

• Java Edition only. Bedrock skins and Bedrock geometry are not supported.
• Only the vanilla box models. There are no custom 3D models or geometry, and no HD skins: mob and skin textures are the vanilla sizes (items, blocks and plants can be HD).
• Layouts follow the Java Edition 1.21 model code: the UV maps were checked against the decompiled code and the vanilla textures of 1.21.1, 1.21.5 and 1.21.11. No texture made with them has been loaded in the game by this project; the checks are the code and the vanilla files. Mobs without a layout (fish, the sniffer, the breeze, the creaking and some others) and saddles cannot be painted yet.
• The views and the 3D preview only model 90° turns. Tilted parts, such as the hoglin's head, a horse's neck or a strider's bristles, are drawn untilted or left out of the views (each layout's note says which).
• check-pack knows the resource pack formats of 1.21 to 1.21.11. It checks structure and references, not how a model or a texture looks in game, and it does not check data packs.
• The art score and the craft advice are heuristics. They have not been validated against human judgment, and they say nothing about whether the texture matches the brief. How good a texture looks depends mostly on the agent writing the spec.
• texel_share, texel_pull and the short links need texel.dev.br: share links are stored there. Long #z= links work without the site's storage. Live sessions don't: the local server serves its own page, and the site's studio is only needed to edit a session. TEXEL_SITE points all of this at another origin.
• Once a day the CLI and the server ask texel.dev.br for version.json to tell the agent about a newer release. The request waits at most 1.5 s, carries no data about the user or the specs, and is skipped when TEXEL_NO_UPDATE_CHECK=1 or CI is set.

Building and testing

You need Node 20 or later.

npm install
npm run typecheck        # tsc --noEmit
npm test                 # vitest: 180 tests, including spawned CLI and MCP server bundles
npm run build            # dist/texel-mcp.mjs and dist/texel.mjs (the npm package)
npm run build:plugin     # plugin/server/texel-mcp.mjs and its THIRD_PARTY_NOTICES.md
npm run measure          # the numbers in Measurements

The npm build keeps the MCP SDK and zod as dependencies. The plugin build bundles them into one file, because a Claude Code plugin has no install step; it is committed, and CI fails if it no longer matches the source. Docs, examples, schemas and the viewer are embedded in both builds. SITE_URL at build time changes the site origin baked into the builds and the docs.

Bump the version in package.json, plugin/.claude-plugin/plugin.json and the skill's metadata.version together, and add a CHANGELOG.md section for it; a test checks both.

License

MIT, see LICENSE. The plugin's single-file server bundles the MCP TypeScript SDK (Apache-2.0, with parts under MIT) and zod (MIT); their licenses are in plugin/server/THIRD_PARTY_NOTICES.md.

Not an official Minecraft product. Not approved by or associated with Mojang or Microsoft.