Custom Rule Entry Checks

When you save a strategy: custom strategy, Studio's behavior checks reject rules that cannot work as written: conditions that contradict each other, entries that match every state, rules that earlier rules make unreachable, and buy sizes that break your risk block. Each section shows a rejected strategy with the error text it produces, followed by a corrected version that saves; the examples use Kalshi and Polymarket. For the three checks that apply only to exits, see Exit Checks.

Contradictory conditions

A rule whose conditions can never all be true, or that compares against a value outside the field's range, can never fire. The classic case is writing cents instead of dollars:

# Rejected: the take-profit uses 60 (cents) instead of 0.60 (dollars)
# error: predicate is contradictory and can never match
version: 1
platform: polymarket
strategy: custom
strategy_name: "Cents instead of dollars (rejected)"
market:
  slug: "will-example-index-close-above-6000-on-2026-12-31"
risk:
  max_position: 10
  price_floor: 0.05
  price_ceiling: 0.95
loop:
  interval: 30
rules:
  - name: take_profit
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: price, op: ">=", value: 60}
    action: sell_all
  - name: stop_loss
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: price, op: "<=", value: 0.25}
    action: sell_all
  - name: buy_yes_in_band
    when:
      all:
        - {field: position_size, op: "==", value: 0}
        - {field: order_count, op: "==", value: 0}
        - {field: price, op: ">=", value: 0.30}
        - {field: price, op: "<=", value: 0.40}
    action: buy_yes
    size: 10

Fixed: write the threshold in dollars.

version: 1
platform: polymarket
strategy: custom
strategy_name: "YES band with dollar thresholds"
market:
  slug: "will-example-index-close-above-6000-on-2026-12-31"
risk:
  max_position: 10
  price_floor: 0.05
  price_ceiling: 0.95
loop:
  interval: 30
rules:
  - name: take_profit
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: price, op: ">=", value: 0.60}
    action: sell_all
  - name: stop_loss
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: price, op: "<=", value: 0.25}
    action: sell_all
  - name: buy_yes_in_band
    when:
      all:
        - {field: position_size, op: "==", value: 0}
        - {field: order_count, op: "==", value: 0}
        - {field: price, op: ">=", value: 0.30}
        - {field: price, op: "<=", value: 0.40}
    action: buy_yes
    size: 10

On Polymarket, price is the YES midpoint and the buy is a limit order at that midpoint, so order_count == 0 keeps the entry from stacking on an unfilled order. Size 10 clears the common 5-share minimum. The same check rejects bands that do not overlap, such as price >= 0.80 together with price <= 0.20, and impossible gates such as position_size < 0.

Entries that always match

An entry that is true for every possible value of the fields it reads is rejected. The usual cause is any used where all was meant: "at least 0.30 or at most 0.70" covers every price.

# Rejected: an any-group band matches every price, with no position gate
# error: entry predicate is exhaustive
version: 1
platform: kalshi
strategy: custom
strategy_name: "OR instead of AND (rejected)"
market:
  series_ticker: KXHIGHNY
risk:
  max_position: 2
  price_floor: 0.05
  price_ceiling: 0.95
loop:
  interval: 30
rules:
  - name: stop_loss
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: unrealized_pnl, op: "<=", value: -0.10}
    action: sell_all
  - name: take_profit
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: unrealized_pnl, op: ">=", value: 0.15}
    action: sell_all
  - name: buy_yes_in_band
    when:
      any:
        - {field: price, op: ">=", value: 0.30}
        - {field: price, op: "<=", value: 0.70}
    action: buy_yes
    size: 1

Fixed: use all for the band and add a position gate.

version: 1
platform: kalshi
strategy: custom
strategy_name: "YES band entry with a position gate"
market:
  series_ticker: KXHIGHNY
risk:
  max_position: 2
  price_floor: 0.05
  price_ceiling: 0.95
loop:
  interval: 30
rules:
  - name: stop_loss
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: unrealized_pnl, op: "<=", value: -0.10}
    action: sell_all
  - name: take_profit
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: unrealized_pnl, op: ">=", value: 0.15}
    action: sell_all
  - name: buy_yes_in_band
    when:
      all:
        - {field: position_size, op: "==", value: 0}
        - {field: price, op: ">=", value: 0.30}
        - {field: price, op: "<=", value: 0.70}
    action: buy_yes
    size: 1

Other entries this check rejects: price >= 0, position_size >= 0, and price < 50 (cents again, always true for a 0 to 1 price).

Unreachable rules

If earlier rules already match every state a rule could match, that rule can never fire. Earlier skip and cancel_all rules count. Here the broad dip entry sits above the narrow one:

# Rejected: prices at or below 0.30 are caught by the rule above
# error: earlier rules make this rule unreachable
version: 1
platform: kalshi
strategy: custom
strategy_name: "Broad rule first (rejected)"
market:
  series_ticker: KXHIGHNY
risk:
  max_position: 2
  price_floor: 0.05
  price_ceiling: 0.95
loop:
  interval: 30
rules:
  - name: stop_loss
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: unrealized_pnl, op: "<=", value: -0.15}
    action: sell_all
  - name: take_profit
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: unrealized_pnl, op: ">=", value: 0.20}
    action: sell_all
  - name: buy_small_dip
    when:
      all:
        - {field: position_size, op: "==", value: 0}
        - {field: price, op: "<=", value: 0.50}
    action: buy_yes
    size: 1
  - name: buy_deep_dip
    when:
      all:
        - {field: position_size, op: "==", value: 0}
        - {field: price, op: "<=", value: 0.30}
    action: buy_yes
    size: 2

Fixed: put the narrower rule first.

version: 1
platform: kalshi
strategy: custom
strategy_name: "Two dip sizes, narrow rule first"
market:
  series_ticker: KXHIGHNY
risk:
  max_position: 2
  price_floor: 0.05
  price_ceiling: 0.95
loop:
  interval: 30
rules:
  - name: stop_loss
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: unrealized_pnl, op: "<=", value: -0.15}
    action: sell_all
  - name: take_profit
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: unrealized_pnl, op: ">=", value: 0.20}
    action: sell_all
  - name: buy_deep_dip
    when:
      all:
        - {field: position_size, op: "==", value: 0}
        - {field: price, op: "<=", value: 0.30}
    action: buy_yes
    size: 2
  - name: buy_small_dip
    when:
      all:
        - {field: position_size, op: "==", value: 0}
        - {field: price, op: "<=", value: 0.50}
    action: buy_yes
    size: 1

Studio pre-fills Max contracts per order from the largest buy size, here buy_deep_dip with 2, so both buys fit that deployment limit. If you lower it to 1 when deploying, the 2-contract buy is refused at runtime; see Size rules.

Entry sizes that break your risk block

A buy's size is checked against the strategy's risk block when you save: it must be positive, at most risk.max_position, and size × risk.price_floor must not exceed risk.max_notional when that is set. An omitted size counts as 1.

# Rejected: the entry buys 5 contracts but the strategy may hold at most 2
# error: entry size exceeds risk.max_position from an empty position
version: 1
platform: kalshi
strategy: custom
strategy_name: "Oversized entry (rejected)"
market:
  series_ticker: KXHIGHNY
risk:
  max_position: 2
  price_floor: 0.05
  price_ceiling: 0.95
loop:
  interval: 30
rules:
  - name: stop_loss
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: unrealized_pnl, op: "<=", value: -0.15}
    action: sell_all
  - name: take_profit
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: unrealized_pnl, op: ">=", value: 0.20}
    action: sell_all
  - name: buy_yes_cheap
    when:
      all:
        - {field: position_size, op: "==", value: 0}
        - {field: yes_best_ask, op: "<=", value: 0.30}
    action: buy_yes
    size: 5

Fixed: size the entry within risk.max_position.

version: 1
platform: kalshi
strategy: custom
strategy_name: "Cheap YES sized within max_position"
market:
  series_ticker: KXHIGHNY
risk:
  max_position: 2
  price_floor: 0.05
  price_ceiling: 0.95
loop:
  interval: 30
rules:
  - name: stop_loss
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: unrealized_pnl, op: "<=", value: -0.15}
    action: sell_all
  - name: take_profit
    when:
      all:
        - {field: position_size, op: ">", value: 0}
        - {field: unrealized_pnl, op: ">=", value: 0.20}
    action: sell_all
  - name: buy_yes_cheap
    when:
      all:
        - {field: position_size, op: "==", value: 0}
        - {field: yes_best_ask, op: "<=", value: 0.30}
    action: buy_yes
    size: 1

The save-time check covers buy_yes and buy_no rules only. Composite orders sizes are not checked against risk.max_position, so keep them within it yourself.