Monorepos in the AI Coding Era (and Why Nx Is Actually Useful)

Part of SAgentLab's AI-Native Engineering series - practical notes for founders building real products.

AI coding changes the economics of software. Code is cheaper. Coordination is not.

That makes repo structure unexpectedly important.

If you have multiple agents working, a monorepo is attractive because:

• shared context is easier
• refactors are safer
• standards are centralized

But monorepos also have sharp edges. Let’s talk about it.

Why monorepos get better with agents

Agents are decent at local edits. They are dangerous at cross-repo changes.

In a multi-repo world, a “simple” change becomes:

• update package A
• publish
• bump dependency in package B
• fix CI
• chase version mismatches

An agent can do this, but the error surface is huge.

In a monorepo:

• all code is visible
• changes are atomic
• refactors can be validated end-to-end

This is basically: reduce the coordination tax.

The big downside: context bloat

Monorepos can become massive. Agents (and humans) suffer:

• slower tooling
• too many similarly named modules
• accidental coupling

The fix is not “don’t use monorepos.” The fix is structure + tooling.

Nx: why it’s a good monorepo management tool

Nx is good because it makes the monorepo less of a free-for-all.

Pros

1. Project graph awareness Nx understands dependencies between packages/apps.

2. Affected commands Run tests/build only for what changed:

   • nx affected:test
   • nx affected:build

   This matters when agents generate lots of small diffs.

3. Generators Standardize new libs/apps with templates. Agents love generators because they remove ambiguity.

4. Caching Repeat builds/tests become much faster.

5. Enforce boundaries You can enforce module boundaries so teams/agents don’t import random internals.

Cons

1. Tooling complexity Nx adds concepts: project graph, executors, plugins. There’s a learning curve.

2. Configuration drift If you don’t keep Nx config clean, it becomes magical and scary.

3. Migration overhead Moving an existing ecosystem into Nx can be a project.

4. Not a substitute for architecture A messy monorepo with Nx is still messy—just faster.

“Multiple repos in one workspace” (bundling) vs true monorepo

You can bundle multiple repos in one folder and pretend.

Pros:

• easy, no migration
• each repo remains independent

Cons:

• cross-repo refactors are still hard
• dependency management stays messy
• CI remains fragmented
• agents lack a single source of truth

Bundling is a decent transitional state. But it doesn’t delete the coordination tax.

When to choose monorepo (practical heuristic)

Choose monorepo if:

• shared libraries change often
• you do cross-cutting refactors
• you want unified lint/test/build
• multiple agents/teams touch the same surfaces

Avoid monorepo if:

• products are genuinely independent
• you need separate security boundaries
• build/test times will explode and you won’t invest in tooling

A simple AI-era rule

If agents are going to touch multiple projects, put them in one place with one set of rules.

Monorepos are not about fashion. They’re about containing agent-induced chaos.

Nx is one of the few tools that makes a monorepo feel like an engineered system instead of a junk drawer.

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If you're trying to ship AI-native features (agents, integrations, data pipelines) without turning your codebase into a demo-driven science project, SAgentLab can help.

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