Modify price, weight, code, or category with option modifiers

How to set it up

Add a modifier to an option value by appending it in curly braces:

<select name="size">
  <option value="Small">Small</option>
  <option value="Medium">Medium</option>
  <option value="Large{p+2.00}">Large</option>
</select>

When a customer selects “Large”, $2.00 is added to the product price.

Modifier syntax

Each modifier supports three operations:

• + — adds to the existing value

• - — subtracts from the existing value

• : — sets the value directly

Chaining multiple modifiers

Multiple modifiers can be chained together using the pipe symbol |:

<select name="size">
  <option value="Small{p-2.00|w-1}">Small</option>
  <option value="Medium">Medium</option>
  <option value="Large{p+2.00|w+1}">Large</option>
</select>

Notes

• Modifiers cannot be applied to standard product parameters (name, price, code, etc.) directly — they must be applied through a custom option value.

• For code modifiers, the code input must appear before the option that modifies it in your form.

• For multicurrency stores, append the currency code to price modifiers where needed, e.g. {p+5CAD}. If no currency code is specified, the store currency is assumed.

• When using cart validation, set initial values high and modify down rather than the other way around — see the Foxy HMAC validation documentation for details.

• The category modifier {y:} is useful for donation forms that offer both one-time and recurring options, switching the product to a subscription category based on the customer’s selection.