Ask HN: What is the best money you have spent on professional development?

That was my instinctive reaction as well: money is more for hiring help or buying equipment now. Most of my "professional development" now starts with online sources, including tutorial/reference information about different technologies and discussions with other developers, and most of that is freely available.

In my earlier years as a developer I also bought a lot of books and some of them were very useful, and from time to time I still find a good one. If I were at the same stage today, I'd probably also consider online training courses, as some of them do look well presented and for getting up to speed quickly in a new area that sort of guided material can be helpful. (The same applies to in-real-life small group training courses, when that sort of thing becomes more practical again.)

I'm not a big fan of convention/lecture formats, though. They tend to charge a lot for admission, and IME they are rarely worth the time and money, particularly because these days you can often find much of the best material from any particularly good presenters available freely from other sources anyway.

I'll say books period. Every month I buy them, every month I read them, and I let the topics sort themselves out.

I found that (for me !) it was less useful to invest in learning to do new things, as opposed to investing in being more efficient and / or having my work time more pleasant.

Make your work feel like pleasure and there is no limit to what you can achieve. So maybe don't only think "what can I be better at ?" but also "how can my life be better while I work ?".

Software:

A proper training session with a high level debugger for a language I wasn't used to, debuggers often have esoteric interface and "hidden" features, but learning to use them comfortably will make your life so much easier and pleasant.

Buying a license for a good IDE (in my case, intellij). I use vs code 70% of my time but when I need to work on more complex pieces of code or debugging it just change your life.

Hardware:

Buying a proper "high quality" laptop, notably the screen (real matte screen because screw glares, and 2k/3k/4k resolution because you look at text all day so crystal clear font rendering matters a lot).

A great chair with proper support because my back hurting at the end of every day is not ok.

A switchable sitting / standing desk ( https://www.autonomous.ai/product/standing-desk ).

Quality noise cancelling headphones (Bose QC 35).

How did you find such a mentor?

Cmon, let’s be honest. A LeetCode subscription.