Excel MCP Server (FsOpenXmlDsl)

Kookerella.FsOpenXmlDsl

A typesafe F# DSL for building Excel workbooks, interpreted into calls against the DocumentFormat.OpenXml SDK. The DSL is a plain data model (records/DUs with structural equality) — the interpreter (Writer) compiles it to OOXML, and the reverse transform (Reader) parses an existing .xlsx back into the same DSL.

See MAPPING.md for exactly which SpreadsheetML features map 1:1, which are approximated, and which aren't modeled yet.

This round-trips in both directions, which most Excel libraries (EPPlus, ClosedXML, NPOI, ...) don't: they give you an imperative API to build a workbook from scratch or mutate an existing one, but no way to turn an existing file back into readable source. Here, Reader parses a real .xlsx/.xlsm back into the same DSL, and Workbook.generateScript (F#) / CsCodeGen.Generate (C#) go one step further and render that model back out as a self-contained script that rebuilds an equivalent file - a decompiler for spreadsheets, not just a writer. Two more surfaces, Xml.ofWorkbook/Xml.toWorkbook (see "## XML" below) and Json.ofWorkbook/Json.toWorkbook (see "## JSON" below), do the same translation to/from plain XML or JSON against a real schema - for a caller who'd rather generate or consume data than write code at all, e.g. an XSLT pipeline producing a report. Kookerella.FsOpenXmlDsl.Mcp exposes all four directions as MCP tools (generatefsharpscript/generatecsharpscript/generatexml/createworkbookfromxml/ generatejson/createworkbookfromjson) for an AI agent, and as fsopenxmldsl-mcp convert/build CLI commands for anyone else - try it on any spreadsheet you already have, no code required:

dotnet tool install -g Kookerella.FsOpenXmlDsl.Mcp
fsopenxmldsl-mcp convert your-file.xlsx --lang csharp

Don't have .NET installed? Download a self-contained build for your platform from the Releases page - no install required.

Demos

Full worked examples of the decompile-then-extend workflow above - reverse-engineering the same invoice template into C#, F#, an XSLT transform, and a plain JSON-generation script, each wired up to real data and real tests proving the result stays schema-valid - live in a companion repo: Kookerella.Demo.DecompileToSource.

Layout

Shortened. The full README is on GitHub.