Paper Trader MCP

A local, durable, simulation-only MCP server for recording US-equity order intents and later estimating outcomes from historical Alpaca SIP NBBO quotes. It never places live orders or Alpaca paper-broker orders. There is no order endpoint, broker SDK, generic fetch tool, trades endpoint, GTC, extended-hours, fractional-share, or partial-fill support.

Install and run

Requirements: Python 3.14, uv, and Alpaca data credentials with historical SIP access.

./setup.sh
export APCA_API_KEY_ID='...'
export APCA_API_SECRET_KEY='...'
./run.sh

The scripts are executable and run.sh uses only this project's .venv. Credentials are read from the environment (the server does not load .env). Recording, listing, and closing intents work without credentials; evaluation requires them because it reads Alpaca's quote and calendar APIs. The database defaults to ~/.local/share/paper-trader/paper-trader.sqlite3; set PAPER_TRADER_DB to override it. See .env.example for bounded quote-policy and commission options.

Defaults you may want to configure

Setting	Default	Meaning
Commission per order	$0	Applied to every simulated fill
Commission per share	$0	Applied to every simulated fill
Order latency	250 ms	Override per order with latency_ms
Quote lookback	120 s	Search window for prevailing top-of-book quote
Maximum quote age	30 s	Older quotes are unusable
Additional slippage beyond spread	$0	Buys still cross to ask; sells cross to bid

Current sell-side SEC Section 31 and FINRA TAF fees are automatic and itemized. Set the commission variables only when modeling a broker that is not commission-free. Short borrow costs, margin interest, dividends, venue fees, rebates, and taxes are not configurable or modeled.

MCP configuration

Claude Code (~/.claude.json, within the desired project entry) or Desktop / Cowork (claude_desktop_config.json) can use the same stdio configuration:

{
  "mcpServers": {
    "paper-trader": {
      "command": "/absolute/path/to/paper-trader-mcp/run.sh",
      "env": {
        "APCA_API_KEY_ID": "YOUR_DATA_KEY",
        "APCA_API_SECRET_KEY": "YOUR_DATA_SECRET"
      }
    }
  }
}

Prefer launching the client from a shell containing credentials rather than writing secrets into configuration. The five tools are paper_trade_record, paper_trade_get, paper_trade_list, paper_trade_evaluate, and paper_trade_close. Mutation calls require a caller-generated unique request_id; exact retries replay while changed input conflicts. submitted_at is accepted only with backtest=true. Evaluation without as_of explicitly selects now - 16 minutes.

Model and safety caveats

This is an intentionally conservative estimate, not an execution simulator. It crosses one complete top-of-book quote (ask to buy, bid to sell), requires the displayed size to cover the entire order, assumes zero additional slippage, and declares resting limits or insufficient depth indeterminate. There is no L2/depth. Quotes must be regular-session, fresh, complete, non-crossed, SIP-feed records on or after 2025-11-03 (Alpaca changed quote-size units then). Equal timestamps retain API ordering and raw nanosecond timestamps. Temporary SIP embargoes use pending_data; model limitations that prevent a defensible fill use the distinct terminal state indeterminate.

DAY eligibility uses Alpaca's New York calendar, including holidays and early closes. Data newer than the 15-minute entitlement plus a one-minute guard is never queried or clamped. Weekend, pre-open, and after-close marks use the most recent session. Multi-session results do not model splits, dividends, ticker changes, short borrow/availability and fees, dividends owed by shorts, halts/LULD, auctions, or quote corrections.

Accounting uses decimal text and cash-flow logic. Configured commissions apply per fill. Sell fees include FINRA's published 2025-2029 equity TAF schedule and the SEC Section 31 rate (zero through 2026-04-03; 0.00002060 thereafter in the verified 2026 period); dates outside explicit SEC ranges produce warnings. TAF is calculated at the published per-share rate without an invented penny minimum or per-fill rounding, capped per trade, and exempted when execution price is below the applicable per-share rate. Results expose commissions, SEC fees, and FINRA fees separately. Snapshots are immutable. SQLite uses WAL, foreign keys, busy timeout, explicit short transactions, and one connection per operation; network requests occur before write transactions.

The only HTTP destinations implemented are redirect-disabled GET requests to:

• https://data.alpaca.markets/v2/stocks/quotes (always feed=sip, one symbol)
• https://paper-api.alpaca.markets/v2/calendar

Authoritative references: Alpaca historical stock quotes, historical stock data, and calendar API.

Tests

Core tests use only the standard library and fake providers, so MCP need not be installed:

PYTHONPATH=src python3 -m unittest discover -s tests -v

No test uses credentials or network access.

License

Copyright 2026 Emile Fortier.

Licensed under the Apache License 2.0.