Tandem

Somebody has to be on duty this week, and next week, and the week after that. Left to a group chat, that argument runs forever. This is a stdio MCP server that settles it: give it this week's pair, get back the whole calendar.

No database, no config file, no cron. Names go in as arguments, the rotation comes out. That's the entire product.

Install

Node >= 18 is all you need. npx fetches the package the first time and caches it. Participants are plain arguments (spaces or commas, your call); with none, it falls back to ROTATION_PARTICIPANTS, and then to Fran,Xabi,Dani.

Claude Code

claude mcp add -s user tandem -- npx -y github:pg-motocard/tandem Fran Xabi Dani

-s user makes it available from any directory. Drop the flag and the scope is local, meaning it only exists inside the folder you ran the command from.

Or by hand in ~/.claude.json, under the top-level mcpServers (the one nested inside projects is the local scope):

"tandem": {
  "type": "stdio",
  "command": "npx",
  "args": ["-y", "github:pg-motocard/tandem", "Fran", "Xabi", "Dani"]
}

Claude Desktop

claude_desktop_config.json (macOS: ~/Library/Application Support/Claude/, Windows: %APPDATA%\Claude\), under mcpServers:

"tandem": {
  "command": "npx",
  "args": ["-y", "github:pg-motocard/tandem", "Fran", "Xabi", "Dani"]
}

Restart the app after saving.

Cursor

~/.cursor/mcp.json (global) or .cursor/mcp.json (per project), under mcpServers:

"tandem": {
  "command": "npx",
  "args": ["-y", "github:pg-motocard/tandem", "Fran", "Xabi", "Dani"]
}

Codex CLI

~/.codex/config.toml:

[mcp_servers.tandem]
command = "npx"
args = ["-y", "github:pg-motocard/tandem", "Fran", "Xabi", "Dani"]

Any other MCP client

If it speaks stdio, it works: command npx, arguments -y github:pg-motocard/tandem <names>. Instead of arguments you can set ROTATION_PARTICIPANTS="Fran,Xabi,Dani".

Local development

npm install once in the repo, then point the client at the file:

"command": "node",
"args": ["/path/to/tandem/index.js", "Fran", "Xabi", "Dani"]

Related MCP server: supershift-mcp

Usage

One tool, pair_rotation(person1, person2, participants?):

• person1 and person2: this week's pair. Type one of them in CAPS and that person stays on for week 2 with somebody else. Shouting is the API.

• participants (optional): a comma-separated list for this call only, leaving your config alone. Handy when someone joins for a fortnight: participants: "Fran,Xabi,Dani,Laura".

Three names minimum, no duplicates — in the config (or the server refuses to boot) and in the parameter (or the call comes back with the error).

The rules

With N participants:

• The calendar runs 2N weeks and everybody shows up 4 times.

• Week 1 is the pair you handed over.

• Exactly one person carries over from each week into the next, so the same pair never happens twice in a row.

• Nobody works three weeks straight.

• Dates start on the Monday of the current week.

The search is randomised, so the same arguments can produce different calendars. Both are correct. Pick your battles.

Tests

npm test

Checks the invariants — week count, appearances, carry-over, no three in a row, the CAPS repeater — with 3, 4 and 5 participants.