AWS Cloud9 is a cloud-based dev environment used to write, test, and debug your serverless applications with just a browser. It is optimized for serverless and is fully integrated with the Lambda environment. You can import functions from the Lambda environment into your Cloud9 deploy functions back into the Lambda environment.

It comes with native support for SAM, so you can generate the templates easily. It comes prepackaged with all the tools you would expect from IDEs for the language of your choice. A customizable IDE can set themes and shortcuts as you expect from a local dev environment.

You can invoke the function locally (or remotely in the actual Lambda environment) using SAM Local under the covers. It comes with integrated debugger with features you would expect from an IDE debugger. You can deploy the function back to the Lambda environment, and invoke it remotely. In this case, the response is received from the actual Lambda environment.