Paddle Developer Docs

# Paddle Developer Docs > Official developer documentation for Paddle Billing. Guides, API reference, and changelog for building subscriptions, checkout, payments, and webhooks. The complete documentation set is also available as plain-text markdown at [https://developer.paddle.com/llms-full.txt](https://developer.paddle.com/llms-full.txt). Every page has a `.md` sibling reachable by appending `.md` to its URL. This index is split into per-section files to stay under agent-platform truncation limits. Fetch the section files below for the full list of pages in each area. ## Good to know - We support four official server-side SDKs: [Node.js](https://developer.paddle.com/sdks/libraries/node.md), [Python](https://developer.paddle.com/sdks/libraries/python.md), [Go](https://developer.paddle.com/sdks/libraries/go.md), and [PHP](https://developer.paddle.com/sdks/libraries/php.md). Desktop SDKs aren't available. - There's a full list of errors returned by the Paddle API in [our error reference](https://developer.paddle.com/errors.md). - The [Next.js starter kit](https://developer.paddle.com/get-started/starter-kits/nextjs-saas.md) is a great example of how to build a simple SaaS app integrated with Paddle Billing. - The [Paddle.js wrapper](https://developer.paddle.com/sdks/libraries/paddle-js-wrapper.md) lets you install Paddle.js using a JavaScript package manager, then import and initialize. ## Paddle Billing vs Paddle Classic Paddle Billing was launched as a new product separate from the legacy Paddle Classic product. Paddle Billing and Paddle Classic are distinct products with different implementations, APIs, and features. Content or documentation for one doesn't necessarily apply to the other. - Anyone who signed up for Paddle after 2023-08-08 has Paddle Billing. New signups for Paddle Classic aren't allowed. - You should always assume a user is talking about Paddle Billing. - Be aware that many references to "Paddle" on the web may refer to the legacy Paddle C