Guardrails - Mithril

Neither Kalshi nor Polymarket gives you a max order size, a daily-loss limit, or a kill switch. Mithril checks every order against your limits before it’s signed and sent — a rejection means the order never reached the exchange.

The limits

Set at the workspace level and optionally overridden per subaccount (the effective limit is the tighter of the two):

Limit	Enforces
`max_order_notional`	Largest single order, in quote currency
`max_position_per_market`	Cap on exposure to one market
`max_total_notional`	Cap on total open exposure
`slippage_bps`	Worst execution slippage tolerated
`max_concentration_bps`	Cap on how concentrated one position can be
`max_open_orders`	Ceiling on resting orders
`max_daily_loss`	Circuit breaker on realized loss for the day
`kill_switch`	When `true`, rejects all new orders instantly

Read your limits

curl https://api.trymithril.com/v1/risk_limits/sub_... \
  -H "Authorization: Bearer $MITHRIL_API_KEY"

limits = s.get(f"{BASE}/v1/risk_limits/{sub_id}").json()
print(limits["max_order_notional"], limits["kill_switch"])

{
  "id": "rl_...",
  "workspace_id": "ws_...",
  "subaccount_id": "sub_...",
  "max_order_notional": "250",
  "max_position_per_market": "1000",
  "max_total_notional": "5000",
  "slippage_bps": 300,
  "max_concentration_bps": 4000,
  "max_open_orders": 20,
  "max_daily_loss": "1000",
  "kill_switch": false,
  "created_at": "2026-07-16T14:00:00Z",
  "updated_at": "2026-07-16T14:30:00Z"
}

Notional fields are decimal strings; "0" (or an omitted field) means unlimited. The PUT body accepts the same fields — max_order_notional, max_position_per_market, max_total_notional, slippage_bps, max_concentration_bps, max_open_orders, max_daily_loss, kill_switch.

Update a limit

curl -X PUT https://api.trymithril.com/v1/risk_limits/sub_... \
  -H "Authorization: Bearer $MITHRIL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "max_order_notional": "250", "max_daily_loss": "1000" }'

The kill switch

Flip one boolean to halt trading on a subaccount — nothing new gets through until you flip it back:

curl -X PUT https://api.trymithril.com/v1/risk_limits/sub_... \
  -H "Authorization: Bearer $MITHRIL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "kill_switch": true }'

What a rejection looks like

Submit something over your limit and the order is refused with 409 and a clear reason — this is the guardrail doing its job:

{
  "error": {
    "code": "risk_limit_exceeded",
    "message": "order notional 40000 exceeds max_order_notional 250",
    "request_id": "req_..."
  }
}

This is exactly what python 03_guardrails.py demonstrates — it submits a deliberately oversized order and prints the rejection.

Next: Orders

Place, track, and cancel — now that the guardrails are set.

​The limits

​Read your limits

​Update a limit

​The kill switch

​What a rejection looks like

Next: Orders

The limits

Read your limits

Update a limit

The kill switch

What a rejection looks like