How to ensure input validation in Cursor-generated code

1---
2description: Numeric input validation rules
3globs: "src/**/*.ts,src/**/*.tsx"
4alwaysApply: true
5---
6
7## Numeric Validation Rules
8- ALWAYS validate numeric inputs at function entry point
9- Prices and monetary values: must be >= 0, max 2 decimal places
10- Quantities: must be positive integers (> 0)
11- Percentages: must be between 0 and 100 inclusive
12- Array indices: must be >= 0 and < array.length
13- Division: ALWAYS check divisor !== 0 before dividing
14- Age/count fields: must be non-negative integers
15- Throw descriptive errors: 'Expected positive integer for quantity, got: ${value}'
16- Use Number.isFinite() to reject NaN and Infinity

1// Cursor Chat prompt (Cmd+L):
2// Create a numeric validation utility module at
3// src/utils/validate.ts with these functions:
4// - assertPositive(value, name) — throws if not > 0
5// - assertNonNegative(value, name) — throws if < 0
6// - assertRange(value, min, max, name)
7// - assertInteger(value, name)
8// - assertFinite(value, name)
9// Each should throw a descriptive error with the field name.
10
11export function assertPositive(value: number, name: string): void {
12  if (!Number.isFinite(value) || value <= 0) {
13    throw new RangeError(
14      `Expected positive number for ${name}, got: ${value}`
15    );
16  }
17}
18
19export function assertNonNegative(value: number, name: string): void {
20  if (!Number.isFinite(value) || value < 0) {
21    throw new RangeError(
22      `Expected non-negative number for ${name}, got: ${value}`
23    );
24  }
25}
26
27export function assertRange(
28  value: number, min: number, max: number, name: string
29): void {
30  if (!Number.isFinite(value) || value < min || value > max) {
31    throw new RangeError(
32      `Expected ${name} between ${min} and ${max}, got: ${value}`
33    );
34  }
35}

1// Cursor Chat prompt (Cmd+L):
2// @src/utils/validate.ts Create a calculateDiscount
3// function that takes price (non-negative), quantity
4// (positive integer), and discountPercent (0-100).
5// Use our validation utilities for boundary checks.
6// Return the final price after discount.
7
8// Expected output:
9import { assertNonNegative, assertPositive, assertRange } from '@/utils/validate';
10
11export function calculateDiscount(
12  price: number,
13  quantity: number,
14  discountPercent: number
15): number {
16  assertNonNegative(price, 'price');
17  assertPositive(quantity, 'quantity');
18  assertRange(discountPercent, 0, 100, 'discountPercent');
19
20  const subtotal = price * quantity;
21  const discount = subtotal * (discountPercent / 100);
22  return Math.round((subtotal - discount) * 100) / 100;
23}

1// Cursor Chat prompt (Cmd+L, Ask mode):
2// @codebase Find all functions in src/ that accept
3// numeric parameters (price, amount, quantity, count,
4// percentage, index, age, etc.) but do NOT have any
5// validation or boundary checks at the start of the
6// function body. List each file, function name, and
7// which parameter needs validation.

1// Select the function body, press Cmd+K:
2// @src/utils/validate.ts Add boundary validation to all
3// numeric parameters using our validation utilities.
4// price must be non-negative, quantity must be a positive
5// integer. Add the checks at the top of the function
6// before any existing logic.