Guides / Financial decisions

Financial decisions · about 12 min

Write your own rule

Write a rule about a stock's price history, read the belief it returns, combine it with forecasts, and act on it daily.

1. Pick a symbol

   Any of the roughly 2,000 US stocks and ETFs covered by ask-by-symbol. This guide uses NVDA; every answer below is real, for the session of 2026-10-30.

2. Write a simple comparison

   In the Playground, set the state to the symbol and add a yes_no question with "ask" instead of "instructions":

   {
     "model": "ora-fin1",
     "state": {
       "symbol": "NVDA"
     },
     "questions": {
       "above_50d": {
         "type": "yes_no",
         "ask": "C > sma(C,50)"
       }
     }
   }

   Open this in the Playground

   {
     "model": "ora-fin1",
     "answers": {
       "above_50d": {
         "type": "yes_no",
         "yes_no": 0.0746,
         "rule": "C > sma(C,50)",
         "basis": "rule"
       }
     },
     "usage": {
       "input_tokens": 291,
       "output_tokens": 4
     },
     "context": {
       "source": "server",
       "symbol": "NVDA",
       "as_of": "2026-10-30"
     },
     "version": "ora-fin-0.1.1"
   }

3. Read the belief

   above_50d is 0.0746: NVDA closed clearly under its 50-day average. A rule answer is a belief, not true/false: 0.50 is exactly on the line, and it moves toward 0.95 or 0.05 the further the reading is past the line, measured on that quantity's normal scale. So C > sma(C,200) at 0.5455 means "above, but only just".

4. Combine with and / or

   Question	Rule	Belief
   above_200d	C > sma(C,200)	0.5455
   rsi_up	rsi(C,14) > 50	0.073
   both	C > sma(C,200) and rsi(C,14) > 50	0.073
   either	C > sma(C,200) or rsi(C,14) > 50	0.5455
   not_above	not (C > sma(C,200))	0.4545

   and takes the lower part (0.073), or the higher (0.5455), not is 1 minus (0.4545). Ask the parts as their own questions too: it shows which one held a combined rule down.

   Open this in the Playground

5. Offsets and windows

   C[-3] is the close three bars ago. Windows take a period: sma(C,50), highest(C,20). The trap: max includes today, highest doesn't. On XLE:

   Question	Rule	Belief
   breakout	C > highest(C,20)	0.6462
   never	C > max(C,20)	0.5
   at_high	C >= max(C,20)	0.5
   up_3d	C > C[-3]	0.8947

   XLE closed at a new 20-session high, so the breakout form is true while C > max(C,20) sits exactly on the line: it can never be more than equal.

   Open this in the Playground

6. Pattern functions

   Candlestick patterns are functions with no arguments. An English question about a pattern compiles to the same thing:

   {
     "model": "ora-fin1",
     "state": {
       "symbol": "NVDA"
     },
     "questions": {
       "inside": {
         "type": "yes_no",
         "ask": "inside_bar()"
       },
       "doji": {
         "type": "yes_no",
         "ask": "doji()"
       },
       "hammer": {
         "type": "yes_no",
         "ask": "hammer()"
       },
       "engulf_bear": {
         "type": "yes_no",
         "ask": "engulfing_bear()"
       },
       "inside_en": {
         "type": "yes_no",
         "instructions": "Is today an inside bar?"
       }
     }
   }

   Question	Belief	basis
   inside	0.0564	rule
   doji	0.0735	rule
   hammer	0.1245	rule
   engulf_bear	0.0932	rule
   inside_en	0.0564	pattern

   None of these patterns is present on NVDA's last bar. The full list is in Rule language.

   Open this in the Playground

7. Mix a rule with a forecast

   A rule says what is true now; a forecast question says what is likely next. One request can hold both, and the next step's actions can use both:

   {
     "model": "ora-fin1",
     "state": {
       "symbol": "NVDA"
     },
     "questions": {
       "trend": {
         "type": "yes_no",
         "ask": "C > sma(C,200)"
       },
       "up_week": {
         "type": "yes_no",
         "instructions": "Will the stock be higher in a week?"
       },
       "drop5": {
         "type": "yes_no",
         "instructions": "Will it drop at least 5% at some point in the next month?"
       }
     },
     "actions": [
       {
         "id": "lean_long",
         "when": "trend >= 0.6 and up_week >= 0.55",
         "do": "slack",
         "connection": "trading-desk",
         "message": "{{symbol}} ({{as_of}}): in trend ({{trend|pct}}) and leaning up a week ({{up_week|pct}})."
       },
       {
         "id": "no_edge",
         "when": "else",
         "do": "slack",
         "connection": "trading-desk",
         "message": "{{symbol}} ({{as_of}}): no edge. Trend {{trend|pct}}, up a week {{up_week|pct}}, 5% drawdown {{drop5|pct}}."
       }
     ],
     "dry_run": true
   }

   Open this in the Playground

8. Act on it (dry run)

   {
     "model": "ora-fin1",
     "answers": {
       "trend": {
         "type": "yes_no",
         "yes_no": 0.5455,
         "rule": "C > sma(C,200)",
         "basis": "rule"
       },
       "up_week": {
         "type": "yes_no",
         "yes_no": 0.527
       },
       "drop5": {
         "type": "yes_no",
         "yes_no": 0.523
       }
     },
     "usage": {
       "input_tokens": 355,
       "output_tokens": 12
     },
     "context": {
       "source": "server",
       "symbol": "NVDA",
       "as_of": "2026-10-30"
     },
     "version": "ora-fin-0.1.1",
     "actions": [
       {
         "id": "lean_long",
         "fired": false,
         "status": "skipped"
       },
       {
         "id": "no_edge",
         "fired": true,
         "status": "dry_run",
         "do": "slack",
         "connection": "trading-desk",
         "preview": {
           "text": "NVDA (2026-10-30): no edge. Trend 55%, up a week 53%, 5% drawdown 52%."
         }
       }
     ]
   }

   trend 0.5455 misses the 0.6 line, so lean_long was skipped and no_edge fired: the preview is exactly what Slack would get. Nothing was sent, because "dry_run": true.

9. Run it daily as a workflow

   Put the same questions and actions in a workflow with a list of symbols and a time (16:45 New York after the close, or 08:30 before the open), press Test run, then untick dry run. See Run a watchlist every day and Send a pre-open digest.

What's next

• Rule language (reference)
• Cookbook: trend filter plus entry trigger
• All cookbooks