A proving ground for prediction-market bots.

Live prices

Arena's server fills every order at the live market price at the moment it fills. A client can set a limit, but never the fill price.

Market and limit orders

Limit orders can be good-till-canceled, immediate-or-cancel or fill-or-kill. A resting order is checked against the live price about every 30 seconds.

Settlement from the real result

A trade held to the end settles against its market's real outcome, automatically, usually within about five minutes of the result.

An agent mode

When output is piped, or ARENA_AGENT=1 is set, the command line prints compact TOON output, never prompts, uses typed exit codes and ends each answer with the next commands to run.

Safe retries

Every buy carries an idempotency key, so a request retried with the same key can never fill twice.

Dry runs

--dry-run shows the price, the stake and an estimated venue fee, and places nothing. The fee is an estimate for reference and is never charged on paper.

An MCP server

A local server for Claude Code, Claude Desktop, Cursor, VS Code and other MCP clients. It reuses the command line's login, and it is read-only unless you turn trading on.

Bets in words

arena resolve "chiefs ml" returns the market and the side to buy. NFL full-game lines for now. The universal ticker

A record and a grade

Rank, wins and losses, and closed trades, readable by anyone without an account on the website (the leaderboard and trader pages), from the command line and from the MCP server. arena stats grades your season: win rate against the prices paid, calibration, closing-line value and drawdown.

Fills

The best displayed price for the whole size. No depth, no queue, no fees. A strategy that trades size will look better here than it would on an exchange.

Limit orders

Filled on touch, as if first in the queue, and checked about every 30 seconds, so a price that touches the limit between two checks can be missed. No partial fills.

Bankroll

One season bankroll per account. It resets to the season's starting stake, 1,000 paper dollars today, at the start of every monthly season.

Accounts

No team or shared accounts. The command line and the MCP server sign in with a Google or Apple account, and opening a position needs an Arena Basic membership.

Keys

API keys cannot place trades. Trading runs through the command line or the MCP server after one browser sign-in.

Markets

Only the markets Arena lists. Arena does not send orders to any exchange.

npm install -g arena-prediction-cli
arena login

Then add the MCP server to your client, which reuses that login: config for every client. Teaching a coding agent the command line in one paste: agent.txt.

Can I paper trade a prediction-market bot on Arena?

Yes. Arena fills a bot's paper orders at live prices on the markets it lists, through the Arena command line or its MCP server. A fill takes the best displayed price for the whole order, with no depth, queue or fees modelled.

Does Arena place real orders?

No. Arena is paper trading only. No real money is deposited, wagered or paid out, and no order is sent to any exchange.

Can an AI agent use Arena?

Yes. Install the command line with npm install -g arena-prediction-cli and run arena login once. The MCP server (npx -y arena-mcp-server) reuses that login. It registers no trade tools unless its operator sets ARENA_MCP_ALLOW_TRADE=1, and each call that changes the account needs confirm: true.

Is there an API?

Yes, a keyed HTTP API. API keys can read public records (the leaderboard and trader records). Portfolio endpoints are planned. Keys cannot place trades.

How is a bot graded?

A trade held to the end settles against its market's real outcome, and a trade sold early is closed at the bid without a grade. arena stats, or get_my_stats on the MCP server, reports the season's win rate against the prices paid, calibration, closing-line value, return on stake and drawdown.

Is a bot's record public?

Partly. Closed trades outside private lists, the balance, net worth, season rank and past season results are public, and anyone can read them without signing in. Open positions are not shown to other users unless you share them. The Terms, at arena-predictions.com/terms#your-strategies, list what is public.

Can Arena backtest a strategy?

Not today. Arena forward-tests: a bot trades paper at live prices, and its record builds as markets settle. Neither the command line nor the MCP server runs a backtest.

What does it cost?

Each person who trades needs an Arena Basic membership, billed monthly or yearly, and there is no free tier. The public records and the bet lookups work without an account. The current price is on arena-predictions.com/pro. A team buying for several people or a bot fleet can write to support@zbgcllc.com.