Improve Codebase Architecture

Surface architectural friction and propose deepening opportunities — refactors that turn shallow modules into deep ones. The aim is testability and AI-navigability.

This command is informed by the project's domain model and built on a shared design vocabulary:

Run the
```
$codebase-design
```
skill for the architecture vocabulary (module, interface, depth, seam, adapter, leverage, locality) and its principles (the deletion test, "the interface is the test surface", "one adapter = hypothetical seam, two = real"). Use these terms exactly in every suggestion — don't drift into "component," "service," "API," or "boundary."
The domain language in
```
CONTEXT.md
```
gives names to good seams; ADRs in
```
docs/adr/
```
record decisions this command should not re-litigate.

Process

1. Explore

Scope before you scan — YAGNI. Deepening a module pays off by making future changes to it easier, so put extra weight on the parts of the codebase that have recently changed. Decide where to look before you look:

If the user named a direction — a module, a subsystem, a pain point — take it, and skip the inference below.
Otherwise, walk back a good stretch of the commit history (
```
git log --oneline
```
) to find the codebase's hot spots — the files and areas that keep coming up — and let those paths pull your attention first. If the changes are scattered with no clear hot spot, widen the net.

Read the project's domain glossary (

CONTEXT.md

) and any ADRs in the area you're touching first.

For a large codebase, spawn a bounded exploration sub-agent to walk the selected scope while you inspect the domain docs and recent history. For a small scope, explore directly. Don't follow rigid heuristics — explore organically and note where you experience friction:

Where does understanding one concept require bouncing between many small modules?
Where are modules shallow — interface nearly as complex as the implementation?
Where have pure functions been extracted just for testability, but the real bugs hide in how they're called (no locality)?
Where do tightly-coupled modules leak across their seams?
Which parts of the codebase are untested, or hard to test through their current interface?

Apply the deletion test to anything you suspect is shallow: would deleting it concentrate complexity, or just move it? A "yes, concentrates" is the signal you want.

2. Present candidates as a visual report

Present a compact Markdown report directly in the conversation. Use a Mermaid diagram only when relationships, flow, or sequence are materially clearer than prose or a table. If the user asks to preserve the report, save the same Markdown where the repository keeps architectural notes.

For each candidate, include:

Files — which files/modules are involved
Problem — why the current architecture is causing friction
Solution — plain English description of what would change
Benefits — explained in terms of locality and leverage, and how tests would improve
Before / After — a small Mermaid diagram or concise mapping illustrating the shallowness and the deepening
Recommendation strength — one of
```
Strong
```
,
```
Worth exploring
```
,
```
Speculative
```
, rendered as a badge

End the report with a Top recommendation section: which candidate you'd tackle first and why.

Use CONTEXT.md vocabulary for the domain, and the
$codebase-design
vocabulary for the architecture. If

CONTEXT.md

defines "Order," talk about "the Order intake module" — not "the FooBarHandler," and not "the Order service."

ADR conflicts: if a candidate contradicts an existing ADR, only surface it when the friction is real enough to warrant revisiting the ADR. Mark it clearly in the card (e.g. a warning callout: "contradicts ADR-0007 — but worth reopening because…"). Don't list every theoretical refactor an ADR forbids.

See REPORT.md for the report structure and diagram guidance.

Do NOT propose interfaces yet. After presenting the report, ask the user: "Which of these would you like to explore?"

3. Grilling loop

Once the user picks a candidate, run the

$grilling

skill to walk the decision tree with them — constraints, dependencies, the shape of the deepened module, what sits behind the seam, what tests survive.

Side effects happen inline as decisions crystallize — run the

$domain-modeling

skill to keep the domain model current as you go:

Naming a deepened module after a concept not in
CONTEXT.md
? Add the term to
```
CONTEXT.md
```
. Create the file lazily if it doesn't exist.
Sharpening a fuzzy term during the conversation? Update
```
CONTEXT.md
```
right there.
User rejects the candidate with a load-bearing reason? Offer an ADR, framed as: "Want me to record this as an ADR so future architecture reviews don't re-suggest it?" Only offer when the reason would actually be needed by a future explorer to avoid re-suggesting the same thing — skip ephemeral reasons ("not worth it right now") and self-evident ones.
Want to explore alternative interfaces for the deepened module? Run the
```
$codebase-design
```
skill and use its design-it-twice parallel sub-agent pattern.

improve-codebase-architecture

NPX Install

Tags

SKILL.md Content

Improve Codebase Architecture

Process

1. Explore

2. Present candidates as a visual report

3. Grilling loop