skills/improve-codebase-architecture/SKILL.md

name, description

name	description
improve-codebase-architecture	Find deepening opportunities in a codebase, informed by the domain language in CONTEXT.md and the decisions in docs/adr/. Use when the user wants to improve architecture, find refactoring opportunities, consolidate tightly-coupled modules, or make a codebase more testable and AI-navigable.

Improve Codebase Architecture

Surface architectural friction and propose deepening opportunities — refactors that consolidate shallow modules into deeper ones with smaller interfaces. The aim is testability and AI-navigability.

A deep module (Ousterhout, "A Philosophy of Software Design") has a small interface hiding a large implementation. Deep modules are easier to test at the boundary and easier for both humans and AI to navigate.

This skill is informed by the project's domain model — CONTEXT.md and any docs/adr/. The domain language gives names to good module boundaries; ADRs record decisions the skill should not re-litigate.

See CONTEXT-FORMAT.md and ADR-FORMAT.md for the file formats.

Process

1. Explore

Read existing documentation first:

• CONTEXT.md (or CONTEXT-MAP.md + each CONTEXT.md in a multi-context repo)
• Relevant ADRs in docs/adr/ (and any context-scoped docs/adr/ directories)

If any of these files don't exist, proceed silently — don't flag their absence or suggest creating them upfront.

Then use the Agent tool with subagent_type=Explore to walk the codebase. Don't follow rigid heuristics — explore organically and note where you experience friction:

• Where does understanding one concept require bouncing between many small files?
• Where are modules so shallow that the interface is 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?
• Where do tightly-coupled modules create integration risk in the seams between them?
• Which parts of the codebase are untested, or hard to test?

The friction you encounter IS the signal.

2. Present candidates

Present a numbered list of deepening opportunities. For each candidate:

• Cluster: which modules/concepts are involved
• Why they're coupled: shared types, call patterns, co-ownership of a concept
• Dependency category: see DEEPENING.md
• Test impact: what existing tests would be replaced by boundary tests

Use CONTEXT.md vocabulary when describing candidates. If CONTEXT.md defines "Order," talk about "the Order intake module" rather than "the FooBarHandler."

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

Do NOT propose interfaces yet. Ask the user: "Which of these would you like to explore?"

3. Grilling loop

Once the user picks a candidate, drop into a grilling conversation. Walk the design tree with them — constraints, dependencies, the shape of the deepened module, what gets hidden, what tests survive.

Side effects happen inline as decisions crystallize:

• Naming a deepened module after a concept not in CONTEXT.md? Add the term to CONTEXT.md — same discipline as /domain-model (see CONTEXT-FORMAT.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. See ADR-FORMAT.md.
• Want to explore alternative interfaces for the deepened module? See INTERFACE-DESIGN.md.