Ask HN: How do you promote a dev tool and build community around it?

I'm sure many of you have launched before a product targeted at fellow developers. I wanted to ask if and how did you manage to get it off the ground before you raised any money?

Let me give you some context first. I'm working on a product for web developers which:

- is free and we intend it to keep it so - is serverless and we host all the necessary backend for it - has a JavaScript library as its frontend - is relatively easy to understand and use - isn't open-sourced (at least not yet) - is ready for a private beta

I guess a reference product you could compare it to is Firebase.

I've always thought the best way to gain the first users would be through tutorials. But it seems these days that if you post somewhere a link to a tutorial of a free product some (many?) will consider it a shameless selfpromotion. At the same time, the web is full of similar content about established products.

What marketing strategy did you use to get your first 10-50-100 beta testers?

thanks, Ann