Arena CLI

# install the binary (the agent prompt and the hook call arena)
npm install -g arena-prediction-cli
arena login

# or try it without installing (arena is not added to your PATH)
npx arena-prediction-cli login

One sign-in is enough. Your agent and the MCP server act with that login. For an agent, install the binary, because the prompt and the hook call arena directly.

Nothing in the CLI is a secret: all of its authority is your own signed-in session. There is nothing else to install for agent use. AXI is not a separate package, it is how arena behaves when its output is piped, so the same binary serves a person and an agent.

$ arena login
arena: opening your browser to sign in. If nothing opens, visit:
  https://<auth host>/authorize?provider=google&redirect_to=http://127.0.0.1:53682/callback…
userId          4d2f8c1e-9b0a-4c6e-8f21-3a7b5d9e0c12
displayName     sharp_joe
isPro           true
balanceDollars  $1,046.00
monthKey        2026-09

Next:
  arena whoami
  arena balance

Providers

arena login --provider apple signs in with Apple instead of Google. There is no guest or anonymous sign-in: the CLI acts for an account, so every trade and every record belongs to the person who signed in.

Headless machines

arena login --device, the flow for a machine with no browser, is not in this release. On a headless box, sign in on a machine that has one and copy ~/.config/arena/credentials.json across.

Where credentials live

In your OS keychain, falling back to ~/.config/arena/credentials.json with mode 0600. The access token lives about an hour and refreshes itself; arena logout deletes the stored pair.

Flags that work everywhere

$ arena balance
dollars           $1,046.00
netWorthDollars   $1,058.40
openStakeDollars  $12.40
monthKey          2026-09

Next:
  arena positions
  arena history

$ arena buy ARENA-EXAMPLE-1 --side yes --contracts 10
Example market — yes @ 62c ask (bid 58c) · stake $6.20 · balance $1,046.00 -> $1,039.80
Fills server-side at the LIVE ask — the fill may differ from this quote.
buy 10 contracts? [y/N] y
placed           true
tradeId          6f1c2a3b-4d5e-4f60-8a71-b2c3d4e5f607
ticker           ARENA-EXAMPLE-1
side             yes
contracts        10
quotedAskCents   62
entryPriceCents  63
stakeDollars     $6.30
idempotencyKey   0b9e8d7c-6a5b-4c4d-9e3f-2a1b0c9d8e7f
slippageCents    1

Next:
  arena positions
  arena sell <trade-id>

$ arena positions
ID                                    MARKET_TICKER              SIDE  CONTRACTS  UNREALIZEDPNLDOLLARS
6f1c2a3b-4d5e-4f60-8a71-b2c3d4e5f607  ARENA-EXAMPLE-1            yes          10                $0.40

totalCount  1

$ arena sell 6f1c2a3b-4d5e-4f60-8a71-b2c3d4e5f607 --yes
sold            true
tradeId         6f1c2a3b-4d5e-4f60-8a71-b2c3d4e5f607
sellPriceCents  67
pnlDollars      $0.40
idempotencyKey  3c2b1a09-8f7e-4d6c-b5a4-93827160f5e4

Three things about that buy

That was a market order: you never set a price, and the fill happens server-side at the live ask, which is why the CLI reconciles the actual fill against the quote and tells you the slippage. --max-price refuses to submit when the quoted ask is above your ceiling. And every buy carries a fresh idempotency key. If the request gets no answer, the CLI retries it with that same key, which can never fill twice. Do not resend the buy yourself: running arena buy again sends a new key and can open a second position, so check arena positions first.

Naming your own price

Pass --limit to place a limit order instead. It fills only at that price or better, and otherwise rests until it fills, reaches --expires, or you cancel it. A resting buy holds the cost out of your balance and returns it in full on cancel; a resting sell holds nothing, because the position is the collateral. --tif ioc or fok never rests. See your resting orders with arena orders and withdraw one with arena cancel.

Specifications

GET https://arena-predictions.com/api/v1/openapi.json is the OpenAPI 3.1 document for the live endpoints; /llms.txt is the short version for a language model. The CLI and the MCP server call the same backends the website does, through arena-core. There is no separate SDK for the HTTP API.