`best_expression`

Compare every instrument that pays off on the given view (above or below a strike at expiry), priced per $1 of payoff net of fees, ranked cheapest first. Ranks ways to express a view; it never says whether to hold one.

Scope: ladder:read

Input

Name	Type	Required	Description
`symbol`	`string`	Required	Underlying ticker, uppercase.pattern ^[A-Z]{1,6}$
`expiry`	`string (date)`	Required	Expiry as YYYY-MM-DD.
`strike`	`number`	Required	The rung's strike.> 0
`side`	`string`	Required	The view: finish above the strike, or below it.one of "above", "below"

JSON Schema

input_schema

{
  "type": "object",
  "properties": {
    "symbol": {
      "type": "string",
      "pattern": "^[A-Z]{1,6}$",
      "description": "Underlying ticker, uppercase."
    },
    "expiry": {
      "type": "string",
      "format": "date",
      "description": "Expiry as YYYY-MM-DD."
    },
    "strike": {
      "type": "number",
      "exclusiveMinimum": 0,
      "description": "The rung's strike."
    },
    "side": {
      "type": "string",
      "enum": [
        "above",
        "below"
      ],
      "description": "The view: finish above the strike, or below it."
    }
  },
  "required": [
    "symbol",
    "expiry",
    "strike",
    "side"
  ],
  "additionalProperties": false
}

Example

Request

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "best_expression",
    "arguments": {
      "symbol": "SPY",
      "expiry": "2026-10-23",
      "strike": 582,
      "side": "above"
    }
  }
}

Result

{
  "symbol": "SPY",
  "expiry": "2026-10-23",
  "strike": 582,
  "side": "above",
  "snapshot_id": "spy-2026-10-23-1760641500000",
  "candidates": [
    {
      "expression": "call_vertical",
      "venue": "tradier",
      "width": 1,
      "unit_cost": 0.512,
      "fees_per_unit": 0.0013,
      "tradable": true,
      "best": true,
      "diff_to_best_cents": 0,
      "legs": [
        {
          "option_symbol": "SPY261023C00582000",
          "action": "buy_to_open",
          "qty": 1
        },
        {
          "option_symbol": "SPY261023C00583000",
          "action": "sell_to_open",
          "qty": 1
        }
      ]
    },
    {
      "expression": "put_vertical_short",
      "venue": "tradier",
      "width": 1,
      "unit_cost": 0.519,
      "fees_per_unit": 0.0013,
      "tradable": true,
      "best": false,
      "diff_to_best_cents": 0.7,
      "legs": []
    },
    {
      "expression": "cash_settled_binary",
      "venue": "cboe",
      "unit_cost": 0.5,
      "tradable": false,
      "best": false,
      "note": "Not tradable at Tradier; routing is v2"
    }
  ]
}

unit_cost is dollars per $1 of payoff, net of fees. Candidates whose quotes failed validation are left out.