Are barrel files a problem for tree shaking when defining internal boundaries?

A barrel isn't automatically a bundle-size problem. Modern bundlers can often remove unused exports, but the result depends on the module graph, side effects, and the tool's configuration. A module that does work at the top level may still need to be included even if its exports aren't used.

Named re-exports can make the public API easier to inspect. Wildcard exports aren't necessarily impossible to shake, but they can make the graph harder to reason about. Keeping internal imports away from the domain's own barrel also helps avoid introducing circular dependencies through that entry point.

Measure it in your actual build. Pick a representative barrel, replace its use with direct imports in a test branch, and compare the production bundle and build time. Check the bundler's output or bundle analysis to see which modules remain and why.

One comparison won't prove every barrel is fine, but it'll give you a more useful starting point than a blanket rule.

If the boundary is valuable, keep the barrel and lint rule. They serve a different purpose from tree shaking: making cross-domain dependencies visible and giving each domain a deliberate public surface.

That is still a convention enforced by tooling, though. Without the rule, someone can generally reach around the barrel with a deep import.

Workspace packages with package.json exports are another option. The exports map defines the package entry points and can prevent consumers from importing unexported package paths through normal package resolution.

That's a stronger package boundary, but it comes with package management overhead. It also doesn't magically fix tree shaking or side effects, so I wouldn't restructure solely on that assumption.

There's also a reasonable case for fewer boundaries. If a domain's public API isn't giving the team much value, direct imports may be simpler than maintaining a barrel and custom rules. That choice depends on how much coupling you're trying to control, not just bundle size.