ModelChoice MCP

An open Model Context Protocol server for Vose Software's ModelChoice — the decision-tree add-in for Excel.

A sibling to modelrisk-mcp: where that server brings Monte Carlo risk modelling into a conversation, this one brings decision analysis — building, reading, rolling back, and analysing decision trees in Excel.

Status: 0.0.12 — Phase 3 (build + drive). 14 tools: build_tree / edit_tree (incl. add/remove options & outcomes) / build_control_panel, read + roll + verify, plus run_evpi / run_evii / run_robustness / run_sensitivity / run_decision_report / run_analysis / read_sheet over ModelChoice's headless commands.

Tools

Tool	What it does
build_tree	Build a tree from a structured description and write it into Excel (dry-run by default). Validates + rolls it back so you confirm the recommendation before writing. The build-from-a-prompt path.
edit_tree	Tweak an existing tree — change probabilities, payoffs, labels, or the objective, add or remove whole options/outcomes (add_option / add_branch / remove_branch), then re-roll it (dry-run by default). The "tweak it by talking" path.
build_control_panel	Lift the tree's inputs into a control panel at the top of the sheet — every probability and cash flow as a labelled cell, with the tree linked back to it, so you drive the whole model from one input block. Drives MC_BuildControlPanel_Auto.
list_trees	List the decision trees in a workbook with node-type counts.
get_tree	Full structure of one tree — decision / chance / terminal nodes, branches, probabilities, values.
roll_up	Roll the tree back to its expected values and optimal policy — the decision recommendation, in plain English.
verify_rollback	Cross-check our rollback against the MC_V_<id> cells ModelChoice itself wrote — a correctness guarantee when the tree has been rendered.
run_evpi	Expected Value of Perfect Information for the active tree — the most you'd pay for perfect information before deciding. Drives ModelChoice's headless MC_EVPI_Auto.
run_evii	Expected Value of Imperfect Information for a specific test — pass the target chance node and a likelihood matrix P(signal|state); returns EVII, its net value after cost (worth running?), and the EVPI ceiling. Drives MC_EVII_Auto.
run_analysis	Run any decision-analysis (robustness, sensitivity, strategy_table, policy_suggestion, decision_brief, mcda_report, risk_profile, evpi) and report the result sheets it produced.
run_robustness	Run the robustness ("break the decision") analysis and return a structured read — verdict, score, and the minimum input change that flips the decision.
run_sensitivity	Run one-way sensitivity and return the tornado-ordered report (which assumptions the decision is most sensitive to) + baseline EV + sheets.
run_decision_report	Run a decision report — strategy_table, policy_suggestion, decision_brief, or mcda_report — and read the primary result sheet back in one call (rows + label→value pairs + related sheets).
read_sheet	Read a result sheet's cells back (numbers / text), e.g. the robustness verdict or a sensitivity report.

Prompt: /design-decision-tree walks an analyst through building a tree from a description (or pasted data) and analysing it.

Run it: uv run python -m modelchoice_mcp (stdio), or wire modelchoice-mcp into Claude Desktop like any MCP server.

How it works

ModelChoice is a C# .NET (Excel-DNA) add-in. Unlike ModelRisk it exposes no COM object model and no compute worksheet functions — but it persists the entire decision tree as JSON in a very-hidden worksheet (_MC_Store), and the rollback logic is fully captured in that model. So this server can:

• Read every tree in a workbook by reassembling the _MC_Store payload (chunked across columns, v2-envelope or v1-legacy format) and parsing the model JSON.
• Roll back each tree to its expected values and optimal policy in pure Python — reproducing ModelChoice's own rollback (terminal payoff = accumulated branch values; chance = auto-normalized probability-weighted EV; decision = max/min by Maximize). No add-in needs to be loaded — it reads the saved model directly.

The Python roller is validated against ModelChoice's own authoritative C# test (Model_Validate_Compile_Rollback_Works): a decision/chance tree that rolls back to EV 50 with the optimal option selected — and matches exactly.

Roadmap

• Phase 0 (done): the read + rollback engine — parse _MC_Store, reconstruct each tree, roll back to EV + optimal policy. Validated against ModelChoice's own C# rollback test.
• Phase 1 (done): the MCP server — list_trees, get_tree, roll_up, proven live against a real workbook.
• Phase 1b (done): verify_rollback cross-checks our EVs against the MC_V_<id> named ranges; CI (ruff + mypy + pytest) and a tag-driven PyPI release pipeline; wheel + sdist build. (First publish awaits a PyPI trusted-publisher; the live MC_V_ cross-check awaits a real rendered tree.)
• Phase 2 (in progress): drive analyses. ModelChoice already ships headless MC_*_Auto ExcelCommands for most analyses (robustness, sensitivity, strategy table, policy, decision brief, MCDA, risk profile); run_analysis + read_sheet drive and read any of them. EVPI and EVII had no standalone commands, so MC_EVPI_Auto (AB#2558) and MC_EVII_Auto (AB#2568) were added with the run_evpi / run_evii tools. Live verification + richer per-analysis result parsing are the remaining work.
• Phase 3: build/edit trees — write the model JSON into _MC_Store and trigger a re-render.

Architecture

A separate server that reuses the patterns proven in modelrisk-mcp (xlwings bridge, dry-run-by-default safety on any future writes, packaging, MCP-registry flow). Decision analysis and Monte Carlo are distinct domains, so they ship as distinct servers.

Development

uv sync --extra dev
uv run pytest        # parser/roller + store-format tests (no Excel needed)

MIT licensed.