Feature Tradeoff API

Overview

Endpoint

POST /api/feature.php

Request Headers

Request Body (JSON)

Validation Rules

• All six fields are required and must be numeric.
• unitsWithoutFeature can be fractional (in millions) and is converted to units by × 1,000,000.
• If any field is missing/invalid JSON, the API returns an error object.

Calculation Model

1. Convert inputs:
   • CI = costIncrease / 100
   • M = currentProfitMargin / 100
   • U = unitsWithoutFeature × 1,000,000
   • P = sellingPrice
   • F = fixedCost × 1,000,000
   • ΔP = extraSellingPrice
2. Current cost & profit per unit:
   • C = P × (1 - M)
   • π = P × M
3. New cost & profit per unit with feature:
   • C' = C × (1 + CI)
   • π' = P - C'
   • Δπ = π - π' (decrease in profit per unit)
4. Loss on base volume:
   • L = Δπ × U
5. Amortized fixed cost (3 years):
   • A = F / 3
6. Total loss to cover:
   • T = L + A
7. Profit per extra unit (with price uplift on incremental units only):
   • P' = P + ΔP
   • g = P' - C'
8. Extra units required:
   • If g ≤ 0, break-even is not feasible.
   • Else extraUnits = ceil(T / g).

Interpretation: If your feature raises unit cost, you incur a loss on the existing plan (same price, same base units). You must cover that loss (plus 1/3 of fixed cost per year) with margin from additional units—optionally aided by a price uplift on those incremental units.

Examples

cURL

{
  "cmd": "curl -s -X POST https://www.promptbox.cn/api/feature.php \\",
  "data": "-H 'Content-Type: application/json' \\",
  "json": "-d '{\"costIncrease\":5,\"currentProfitMargin\":49.5,\"unitsWithoutFeature\":5,\"sellingPrice\":1,\"fixedCost\":1,\"extraSellingPrice\":0.10}'"
}

HTTPie

http POST https://www.promptbox.cn/api/feature.php \
Content-Type:application/json \
costIncrease:=5 currentProfitMargin:=49.5 unitsWithoutFeature:=5 \
sellingPrice:=1 fixedCost:=1 extraSellingPrice:=0.10

JavaScript (fetch)

await fetch("https://www.promptbox.cn/api/feature.php", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    costIncrease: 5,
    currentProfitMargin: 49.5,
    unitsWithoutFeature: 5,
    sellingPrice: 1.00,
    fixedCost: 1.00,
    extraSellingPrice: 0.10
  })
}).then(r => r.json());

PHP

<?php
$payload = [
  "costIncrease" => 5,
  "currentProfitMargin" => 49.5,
  "unitsWithoutFeature" => 5,
  "sellingPrice" => 1.00,
  "fixedCost" => 1.00,
  "extraSellingPrice" => 0.10
];

$ch = curl_init("https://www.promptbox.cn/api/feature.php");
curl_setopt_array($ch, [
  CURLOPT_POST => true,
  CURLOPT_HTTPHEADER => ["Content-Type: application/json"],
  CURLOPT_POSTFIELDS => json_encode($payload),
  CURLOPT_RETURNTRANSFER => true,
]);
$out = curl_exec($ch);
curl_close($ch);
echo $out;

Python

import requests
r = requests.post(
  "https://www.promptbox.cn/api/feature.php",
  json={
    "costIncrease": 5,
    "currentProfitMargin": 49.5,
    "unitsWithoutFeature": 5,
    "sellingPrice": 1.00,
    "fixedCost": 1.00,
    "extraSellingPrice": 0.10
  },
  headers={"Content-Type":"application/json"}
)
print(r.json())

Responses

200 OK – Success

Returns computed totals. Currency values are rounded to 2 decimals; extraUnitsNeeded is an integer count (rounded up).

{
  "lossFromInitialUnits": 123456.78,
  "totalLossWithFixed": 223456.78,
  "extraUnitsNeeded": 456789
}

200 OK – Not Feasible

If incremental unit profit ≤ 0, break-even cannot be achieved by selling more units.

{
  "lossFromInitialUnits": 123456.78,
  "totalLossWithFixed": 223456.78,
  "extraUnitsNeeded": "Not feasible (profit per extra unit ≤ 0)"
}

200 OK – Error Object

If the payload is missing or malformed, you receive an error description.

{
  "error": "Invalid JSON input."
}

Content-Type

All responses use application/json.

HTTP Status Codes

Design choice: validation issues are returned with HTTP 200 and an error field for simplicity in clients.

JSON Schema (informal)

{
  "type": "object",
  "required": [
    "costIncrease",
    "currentProfitMargin",
    "unitsWithoutFeature",
    "sellingPrice",
    "fixedCost",
    "extraSellingPrice"
  ],
  "properties": {
    "costIncrease": { "type": "number", "description": "Percent (e.g. 5 => 5%)" },
    "currentProfitMargin": { "type": "number", "description": "Percent gross margin" },
    "unitsWithoutFeature": { "type": "number", "description": "Millions of units per year" },
    "sellingPrice": { "type": "number", "description": "USD per unit" },
    "fixedCost": { "type": "number", "description": "USD millions" },
    "extraSellingPrice": { "type": "number", "description": "USD per unit uplift on incremental units" }
  }
}

Worked Example

Inputs:

{
  "costIncrease": 5,
  "currentProfitMargin": 49.5,
  "unitsWithoutFeature": 5,
  "sellingPrice": 1.00,
  "fixedCost": 1.00,
  "extraSellingPrice": 0.10
}

Key steps (rounded here for readability):

C = 1.00 × (1 - 0.495) = 0.505
C' = 0.505 × (1 + 0.05) = 0.53025
π = 1.00 × 0.495 = 0.495
π' = 1.00 - 0.53025 = 0.46975
Δπ = 0.495 - 0.46975 = 0.02525

U = 5 × 1,000,000 = 5,000,000
L = 0.02525 × 5,000,000 = 126,250
A = 1,000,000 / 3 ≈ 333,333.33
T = 126,250 + 333,333.33 ≈ 459,583.33

P' = 1.00 + 0.10 = 1.10
g = 1.10 - 0.53025 = 0.56975
extraUnits = ceil(459,583.33 / 0.56975) ≈ 807,018

You would need approximately 807,018 incremental units per year to break even under these assumptions.

Edge Cases & Gotchas

• If extraSellingPrice = 0 and the feature raises costs, g may be small; required units can become very large.
• If g ≤ 0 (e.g., price uplift too low or cost increase too high), the API returns “Not feasible…”.
• All currency math is done in decimal floats; returned currency values are rounded to two decimals.
• Fixed cost is amortized as fixedCost × 1,000,000 / 3 per year (3-year straight-line).

Security & CORS

The endpoint allows cross-origin requests via Access-Control-Allow-Origin: *. No authentication is required. Do not send sensitive data.

Changelog

Support

Questions or issues? Open an issue with a reproducible example (request body and the JSON you received), or contact the site owner.