JsRates

JsRates is a Shopify application that gives merchants and developer partners the ability to take full control over shipping rate calculations using custom JavaScript logic. Unlike standard flat-rate or weight-based shipping methods, JsRates enables users to write their own shipping rules in JavaScript, test them directly against real Shopify checkout data, and deliver accurate, context-aware shipping options to customers. The app is built specifically for the Shopify ecosystem, including Shopify Plus stores, and is designed to handle high-volume checkout traffic without sacrificing reliability. The core functionality revolves around a built-in JavaScript Shipping Logic Editor. Merchants or developers can write custom functions that determine shipping rates based on any variable available in the checkout payload: cart total, item weight, dimensions, destination address, product tags, customer tags, discount codes, or even external API calls. The editor includes a test payload feature that populates with realistic order data, allowing immediate validation of the JavaScript code before it goes live. This reduces the risk of errors at checkout and speeds up iteration. For non-technical merchants, JsRates offers a free setup service where the team writes and configures the shipping logic on the merchant's behalf. This makes advanced custom shipping accessible to store owners who are not comfortable with coding. For developers and agency partners, the app provides a clean, documented API and a workflow that integrates into existing development pipelines. It supports version control, so changes to shipping logic can be rolled back if needed. JsRates is especially useful for stores with complex shipping requirements: multiple warehouses, real-time carrier rates that need custom