crochetpatterngen-engine

The deterministic photo-to-crochet-chart engine behind crochetpatterngen.com — packaged as a Python library, CLI, and MCP server so AI agents (Claude Desktop, Cursor, etc.) can turn photos into crochet charts with exact stitch counts.

Deterministic, not generative. There is no AI image generation here — just resize, median-cut color quantization, and confetti cleanup. Same input, same chart, same stitch counts, every time. No hallucinated rows.

Why this engine

Real stitch counts — every chart comes with per-color hex + stitch counts that sum exactly to the grid size. What you see is what you crochet.
C2C block aspect correction — C2C blocks are physically wider than tall (0.7:1 h:w). The engine adjusts grid dimensions so the worked piece keeps the photo's proportions instead of coming out squashed.
5 technique presets — graph, c2c, tapestry, mosaic, filet.
Yarn estimation — per-color yardage for 6 yarn weights (fingering → super bulky).
Zero heavy deps — Pillow + numpy only. Optional rembg extra for background removal.

Install

pip install crochetpatterngen-engine          # core
pip install crochetpatterngen-engine[mcp]     # + MCP server
pip install crochetpatterngen-engine[rembg]   # + background removal

Python API

from PIL import Image
from crochet_chart_engine import generate_chart, render_design, estimate_yarn

png_bytes, meta = generate_chart(
    Image.open("photo.jpg"),
    technique="c2c",     # graph | c2c | tapestry | mosaic | filet
    grid_w=60,           # 20..120
    n_colors=8,          # 2..16
)
# meta: {"grid_w", "grid_h", "colors": [{"hex", "count"}],
#        "total_stitches", "technique", "warning"}

yarn = estimate_yarn(meta, weight="worsted")
# {"total_yards": ..., "colors": [{"hex", "count", "yards"}], ...}

png_bytes, meta = render_design("designs/frog.txt")  # ASCII design -> chart

CLI

crochet-chart chart photo.jpg out.png --technique c2c --grid-w 60 --colors 8
crochet-chart design designs/frog.txt frog.png
crochet-chart yarn photo.jpg --technique graph --weight worsted

MCP server (Claude Desktop & friends)

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "crochet": {
      "command": "uvx",
      "args": ["--from", "crochetpatterngen-engine[mcp]", "crochetpatterngen-mcp"]
    }
  }
}

Or with a regular pip install:

{
  "mcpServers": {
    "crochet": {
      "command": "python",
      "args": ["-m", "crochet_chart_engine.mcp_server"]
    }
  }
}

Tools exposed (stdio transport):

Tool	What it does
`photo_to_chart`	Local image path → chart PNG (base64 or saved to `output_path`) + per-color stitch counts JSON
`render_ascii_design`	ASCII design file → chart PNG + stitch counts
`estimate_yarn_tool`	Stitch counts → per-color yardage for one yarn weight or `all`

ASCII design format

See designs/frog.txt and designs/dragon.txt:

# comment
palette: G=#58A05C, W=#FFFFFF, .=#FAFAF7
title: Frog Face
technique: graph
---
..GGGG..........GGGG....
.GGWWGG........GGWWGG...

One character per stitch; . is the background/padding color. Rows are padded to the longest row.

Development

pip install -e .[dev,mcp]
pytest tests/

License

MIT — see LICENSE.

Free web tool + pattern library at crochetpatterngen.com.

crochet engine