As far as I can tell, the ESBuild plugin does not look at tsconfig.json.

It uses the ESBuild's Transform API, which would require the plugin to explicitly pass the contents of the tsconfig.json file via the tsconfigRaw option.

So far not reading the tsconfig.json hasn't presented any significant problems for me, but the fact that my changes to that file had no effect on web-dev-server was confusing. I would suggest either documenting the fact that the tsconfig.json file is ignored or adding an option to specify the path to the tsconfig.json file.

If either of those sounds good, or you have some other idea, I'm happy to create a PR.