MatPlotLibNet.Mcp

MatPlotLibNet.Mcp

mcp-name: io.github.xkqg/matplotlibnet

An MCP (Model Context Protocol) server for MatPlotLibNet. It gives an AI agent (Claude Code, VS Code, Claude Desktop, or any other MCP host) five tools:

tool	what it does
render_chart	renders a chart spec to a PNG image the model can look at
save_chart	writes the chart as PNG, SVG or PDF to a file and returns the path it wrote
chart_data_table	returns the chart's data as markdown tables, so the model can read exact values, which it cannot read off a picture
list_chart_types	lists the chart types the spec accepts; the list is read from the library's own registry
describe_chart_schema	describes the fields of the spec and gives a worked example for a chart type

The server communicates over stdio. It is a .NET tool: a host runs it with dnx MatPlotLibNet.Mcp (the .NET 10 SDK resolves and starts it), or with dotnet tool exec MatPlotLibNet.Mcp.

{
  "servers": {
    "MatPlotLibNet.Mcp": {
      "type": "stdio",
      "command": "dnx",
      "args": ["MatPlotLibNet.Mcp", "--yes"]
    }
  }
}

The spec

The spec is the library's own figure JSON: the same document that figure.ToJson() writes and ChartSerializer.FromJson reads. The agent can therefore ask for any chart the library can draw:

{
  "width": 800, "height": 600, "title": "Revenue",
  "subPlots": [{
    "series": [{ "type": "line", "xData": [1, 2, 3, 4, 5], "yData": [2, 4, 3, 5, 1], "label": "Q1" }]
  }]
}

The server validates the spec before it renders. It rejects an unknown field, an unknown chart type, a misspelled enum value, a colour the library does not know, or a missing size. The error message names the field that is wrong, so the model can correct the spec instead of receiving a blank picture.

What comes back

render_chart returns the PNG as an image block. Beside it, it returns a short text summary (chart types, series, axis ranges), so a model that cannot see the image still knows what it made. SVG and PDF output is large, so it goes to a file through save_chart and is never returned inline.

The SVG this server writes stores text as glyph outlines (<path>), not as <text> elements. This is because the PNG backend is loaded in the same process, and the library then embeds its own font so that the drawing is identical everywhere.

Limits

• save_chart writes only under one directory: the system temp directory, or the one named by the MATPLOTLIBNET_MCP_OUTPUT_ROOT environment variable. It never overwrites an existing file unless asked.
• Arabic and Hebrew text work without setup. For Devanagari, Thai, Chinese, Japanese or Korean, name font files or directories of font files in the MATPLOTLIBNET_FONTS environment variable, separated by ;; they are registered when the server starts. A bad entry is logged and skipped.
• The server refuses a canvas larger than the documented ceiling, and the error message states the ceiling.

License

MIT — see the repository.