formulon-mcp
@libraz/formulon-mcp is a stdio MCP server for Formulon. It gives AI agents a controlled way to open .xlsx workbooks, inspect structure, edit cells and sheets, recalculate formulas, search and replace text, and save the result — without Excel and without writing a host integration first.
Use it when the workbook is the artifact you want the agent to operate on, not just a file to summarize.
Glossary: MCP (Model Context Protocol)
An open protocol for giving AI agents structured tools and resources. A server exposes typed tool definitions over stdio or HTTP; a client (Claude Desktop, Claude Code, Codex CLI, …) connects and lets the model call those tools with validated inputs.
Glossary: stdio transport
The simplest MCP transport. The client launches the server as a child process and talks JSON-RPC over its stdin / stdout. No network, no ports — the OS process boundary is the security boundary.
- Agent / LLM
- MCP clientClaude Desktop / Code / Codex
- formulon-mcpJSON-RPC over stdio
- Allowlist dispatch
- Session tablesessionId → Workbook
- Workbookvia @libraz/formulon
- *.xlsx
The first two steps run in the host process (whatever runs the MCP client); everything from formulon-mcp onward runs in the server's own child process, reachable only over stdio.
Where to start
| Page | When to read |
|---|---|
| Install | Add formulon-mcp to Claude Code, Claude Desktop, Codex CLI, or any stdio-capable client |
| Workflow | Session model, mutation patterns, recalc / save loop |
| Tools | Detailed tool reference grouped by category |
| Security model | Allowlist, session isolation, what the server will and will not do |
Package
The MCP server is published as @libraz/formulon-mcp and depends on the Formulon WASM package. Current releases accept the @libraz/formulon 0.9 line and resolve to the latest compatible package through your package manager. It requires Node.js 22 or newer.
npx -y @libraz/formulon-mcpNo project checkout is required for typical use — MCP clients run the published package through npx.
What it is not
- Not a chat front-end. It is a tool server.
- Not a sandbox for running arbitrary code. Only allowlisted
Workbookmethods are reachable. - Not a viewer. Hand the bytes to
formulon-cellfor a browser surface.