I run a slightly bigger startup than the one you're at and FWIW, I really appreciate it when employees tell me that they are looking for work elsewhere. If you

I run a slightly bigger startup than the one you're at and FWIW, I really appreciate it when employees tell me that they are looking for work elsewhere. If you are an engineer (I assume you are since you are talking/worrying about technical debt) you are extremely employable. You will probably get a much better opportunity if you are able to look around while at your current company. Interviewing behind your companies back can be logistically tough and can lead to a worse offer. It's possible that your company might march you out the door if you tell them you are leaving. I think this would be a real asshole move and not in their interest but it could happen. If this puts you in a major financial bind it might not be worth the risk, but if you are ok with this I think it is probably better for you to let them know. I don't think you have an obligation to let them know but I think it's probably in your interest.