What are module boundary rules in Nx and why do they matter?

Nx lets you tag each project (e.g., scope:checkout, type:feature, type:util) and then write ESLint rules that restrict which tags can import from which.

// .eslintrc.json
"@nx/enforce-module-boundaries": ["error", {
  "depConstraints": [
    { "sourceTag": "type:feature", "onlyDependOnLibsWithTags": ["type:ui", "type:util", "type:data-access"] },
    { "sourceTag": "scope:checkout", "notDependOnLibsWithTags": ["scope:profile"] }
  ]
}]

Why this matters:

• Prevents accidental coupling between business domains (checkout code importing profile internals).
• Keeps the dependency graph a DAG — no cycles between feature libraries.
• Catches violations at lint time (CI) before they become architectural debt.
• Makes it safe to eventually extract a domain into its own repo or microfrontend — no hidden cross-domain dependencies.