expense-splitter (MCP tool for splitting group expenses)

An expense-splitting MCP server that models group debts as a directed graph. It supports equal, percentage, and weight-based splits, then produces clear settlements and an exportable DOT graph of all obligations.

Demo videos:

Why this exists

Expense splitting is naturally a graph problem: people are nodes, and each expense adds directed edges (who owes whom, and how much). This tool keeps that model explicit, making settlement math transparent and easy to audit.

Features

• Graph-based debt model with DOT export for visualization.
• MCP elicit flows for missing inputs (group name, members, amounts, splits).
• Split methods: equal, percentage, weights.
• Clear settlements derived from the raw debt graph.
• Simple, in-memory group store (no external database).

Tooling overview

These tools are exposed via MCP:

• create_group: create a new group.
• list_groups: list all groups in memory.
• add_people: add one or more people to a group.
• add_expense: add an expense with split details.
• get_group_info: returns members, settlement details, and DOT graph.

Getting started

Requirements

• Go 1.25.1 (as declared in go.mod).
• Optional: Graphviz if you want to render DOT graphs as images.

How to use this MCP server (stdio)

Configure your MCP client to launch the server via stdio. First compile the binary and copy it to /tmp/. Then configure Claude Desktop to use the MCP tool locally.

go build .
cp expense-splitter /tmp/expense-splitter

To use it with a demo agent that I built, see instructions in: https://github.com/vnaveen-mh/expense-splitter-demo-agent

Example flow (conversation style)

User: create a group called napa-trip
Agent: OK — group created.

User: add alice, bob, charlie to the group
Agent: Added Alice, Bob, and Charlie.

User: add an expense by alice for lunch, 120
Agent: Expense added.

User: get group details
Agent: returns members, settlements, and a DOT graph

DOT graph export

The get_group_info tool returns a graph_dot field that you can paste into Graphviz tools:

digraph "napa-trip" {
  "alice" [label="Alice"];
  "bob" [label="Bob"];
  "charlie" [label="Charlie"];
  "alice" -> "bob" [label="$25.00"];
  "alice" -> "charlie" [label="$20.00"];
  "bob" -> "alice" [label="$40.00"];
  "bob" -> "charlie" [label="$20.00"];
  "charlie" -> "alice" [label="$40.00"];
  "charlie" -> "bob" [label="$25.00"];
}

Render to PNG with Graphviz:

dot -Tpng temp.dot -o temp.png

Notes

• All groups and expenses are stored in memory only (no persistence).
• Group names and person names are validated for simple, readable identifiers.
• Privacy/logging: info-level logs avoid names and amounts; enable debug-level logs only when you need detailed troubleshooting output.