Use compoundsim in your AI assistant

compoundsim is also an MCP server. Add it to Claude, ChatGPT or another assistant that supports the Model Context Protocol, and the assistant can run the simulators for you and link to each scenario on this site.

Server URL

https://compoundsim.app/mcp

What it looks like

I invest $500 a month. Compare the S&P 500 and an all-country fund over 20 years.

The assistant calls compare_portfolios and answers with each fund's range of outcomes (10th to 90th percentile), its deepest fall along the way, and a link that opens the same simulation here.

Add it to your assistant

Claude (web and desktop)

Open Customize, then Connectors, and add a custom connector. Name it compoundsim and paste the server URL; no sign-in is needed. A connector added on the web also appears in the desktop app.

ChatGPT

Turn on developer mode in the settings, then create a custom connector (app) with the server URL and no authentication. Menu names and the plans that allow this change often; check OpenAI's help pages if yours differ.

Claude Code

Run this in a terminal:

claude mcp add --transport http compoundsim https://compoundsim.app/mcp

Cursor, VS Code and other clients

Add the server URL as a remote (Streamable HTTP) server, for example:

Cursor (~/.cursor/mcp.json)

{
  "mcpServers": {
    "compoundsim": {
      "url": "https://compoundsim.app/mcp"
    }
  }
}

VS Code (.vscode/mcp.json)

{
  "servers": {
    "compoundsim": {
      "type": "http",
      "url": "https://compoundsim.app/mcp"
    }
  }
}

Tools

simulate_portfolio: Monte Carlo simulation of monthly investing in one asset or a mix: the range of outcomes by year, the deepest fall and the mix's past return.
compare_portfolios: The same plan run through 2 to 4 portfolios, side by side.
simulate_withdrawal: Spending down a balance in retirement: how often the money lasts, and the success rate at withdrawal rates from 2% to 8%.
simulate_fixed_rate: Compound interest at a fixed annual return, year by year.
get_asset_returns: Past annualised returns, dividends and volatility of the 13 assets, in any of 19 currencies.

Things to ask

How likely is a 4% withdrawal from a 60/40 portfolio to last 30 years?
If I invest $300 a month in the S&P 500 for 25 years, what does a bad case look like?
Compare 100% stocks with the all-weather mix over 15 years, starting with $50,000.
What has gold returned per year over the last 20 years, measured in euros?

Good to know

No account, sign-in or API key: the server only runs simulations on public index data.
The server keeps nothing between requests; the numbers you send are used for that simulation only.
Results are simulations from past data, not forecasts or investment advice. Each answer links to the same scenario here, with the same figures on the same day (UTC), so you can check and adjust it.