By Wallace Ferreira2 min read

Enforcing the Dependency Rule in a Monorepo

The package manifests and lint rules that keep core, application and infra pointing inward, and the two places where the rule is still only a convention.

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This monorepo follows one rule above all others: dependencies point inward.

core ← application ← infra ← site / admin

The domain knows nothing about the use cases, the use cases know nothing about Prisma, and only the apps know about Next.js. A rule like that doesn't hold because it is in a diagram. It holds where a tool refuses to let it break. Here is where each tool does that, and where nothing does yet.

Wall 1: package.json is the dependency graph

Each layer is its own package, and a package can only import what it declares:

// packages/core/package.json
"dependencies": { "@repo/utils": "workspace:*", "uuid": "^10.0.0" }
 
// packages/application/package.json
"dependencies": { "@repo/core": "workspace:*", "@repo/utils": "workspace:*" }

Adding next or @prisma/client to core is not a quiet import. It is a visible change to a manifest, and it shows up in review as exactly what it is.

Wall 2: lint bans frameworks in the application layer

application gets its own ESLint config with a no-restricted-imports entry per framework:

{
  group: ['@prisma/*', 'prisma'],
  message:
    'Application layer cannot import Prisma — violates Clean Architecture dependency rule.',
},

React, Next.js, HTTP clients and the email SDK get the same treatment. The message names the rule, so whoever hits it learns why, not only what.

Wall 3: only public exports, and test helpers stay in tests

Every package shares two more patterns. SRC_PATHS forbids reaching into another package's /src, so packages talk through their exports. TEST_HELPERS keeps @repo/core/testing, the test-data builders, out of production code. Test files get the same rule without that ban.

Wall 4: inside the app, features don't reach into routes

apps/site has the same idea one level down: code in src/features/ may not import from src/app/. Route files compose features; features never depend on a route.

Where the walls stop

Two parts of the rule are still conventions, checked in review:

  • core has no framework ban in lint. Only its package.json keeps React or Prisma out.
  • 'use client' components must not import @repo/application. Nothing fails today if one does. A server-only import in the server container would turn that into a build error.

Writing down the gaps is part of the rule. A wall you think exists is worse than one you know is missing.

About the author

Wallace Ferreira