Excel — installation and sideloading

The merton Excel add-in is two pieces:

  1. A small FastAPI server that runs locally and exposes the =MERTON.* formulas.

  2. An Office.js manifest XML that tells Excel where to find the server.

Install the extra

uv pip install "merton[excel]"

This pulls in xlwings, fastapi, uvicorn, openpyxl, xlsxwriter, jinja2, and httpx.

Sideload the add-in

merton excel install --url http://localhost:8000

This writes merton-manifest.xml into your Excel sideload directory:

  • macOS — ~/Library/Containers/com.Microsoft.Excel/Data/Documents/wef/

  • Windows — %LOCALAPPDATA%\Microsoft\Office\16.0\Wef\

  • Linux / others — ~/.config/merton/excel/ (manual upload via Excel on the web)

To verify:

merton excel status

Start the server

merton excel server start --port 8000

Leave the terminal running while you use Excel. To run it detached:

merton excel server start --background
merton excel server stop

Activate the add-in in Excel

  1. Open Excel (desktop or web).

  2. Insert → My Add-ins → Shared Folder (or Upload My Add-in on the web).

  3. Pick merton.

  4. Try =MERTON.DD(100, 0.30, 35, 0.04, 1).

Excel will fetch the function metadata, register the namespace, and autocomplete every MERTON.* formula.

Uninstall

merton excel server stop
merton excel uninstall

Classic UDF fallback (Windows desktop only)

If you can’t run a local server (e.g. inside a locked-down workstation), the same formulas register as classic xlwings UDFs via merton.excel.udf. Configure xlwings to point at that module, then the formulas are available without the FastAPI server. See Building a live Excel credit dashboard for the full setup.