martian VS serverless-localstack

Or put the API definitions into some database (sqlite, datascript + nodejs or babashka or nbb), then you can decide what http library or mocked http solution would you like to use, eg https://github.com/oliyh/martian

Most of the code is just a thin veneer over that information...

There's a lot of concerns at the API edge of a system I would be looking at something like https://github.com/oliyh/martian this for an API and take half those concerns out of your current function

Great point. Fully agree that providing a first-class local development experience is critical to the overall story of application development frameworks.

I guess the main difference is that frameworks like Serverless provide a great experience if you fully buy into their way of doing things (i.e., implement your application assets in the Serverless YAML DSL, etc), whereas LocalStack is a generic platform that works on the API emulation level, hence integrates with most tooling out of the box.

Making the switch from Serverless to, say, AWS CDK, or AWS SAM, or Architect framwork may not be as seamless - however, for each of these frameworks you can always run the local emulation natively on LocalStack. This can help reduce the overall vendor lock-in effect that a lot of application development frameworks come with.

In fact, LocalStack also provides an integration with Serverless [0] - among many other tools [1].

[0] https://github.com/localstack/serverless-localstack