How do you know when you are senior level dev? What’s the threshold?

A bit of a cheesy answer: a junior dev can solve problems, a senior dev can identify them.

Also: a senior dev is someone people turn to for solutions, both from within the team but also for other teams.

it's not a clear distinction, but more of a spectrum. my rough take is:

juniors need help to do their work

mid-levels _can_ use help to improve

seniors provide help based on their experience

it mostly shows from how others speak to you. If people ask you for help frequently and you're able to help them, then you're reaching seniority in that field...

But realistically, I mean... the term senior is more of an HR thing so you can barter for better pay, and for that you only need years of experience. You could be a complete klutz but have 5+ years of experience and you'll technically be eligible for a senior position despite being a nuisance at best. You can see this happen whenever someone who is your "senior" is a complete moron and most likely a "know-it-all" despite knowing nothing. *sigh*

People often misunderstand seniority levels. There’s a big difference between having a senior knowledge of a tool(s) or a language and being a senior engineer as a whole.

For example, “senior react engineer” (i hate these job posting a lot) is a front end developer with a great deal of experience in react library - that person is not a senior engineer.

Ask your hr. Different companies have different definitions of seniority levels.