v1.0 to v1.0
75 added, 62 removed. Audit A to A.
---
name: improve-codebase-architecture
- description: >-
- Identify architectural friction and propose deepening opportunities for testability using
- deletion-test, seam, locality vocabulary
- allowed-tools: Read Grep Glob Bash Write Edit
+ description: >
+ Scan a codebase for deepening opportunities, present them as a visual HTML report, then grill
+ through whichever one you pick. Use when the user wants architecture improvement candidates
+ surfaced before choosing one. Triggers on: improve the architecture, find deepening
+ opportunities, where should we refactor.
+ allowed-tools: Read Grep Glob Bash Write Edit Task
compatibility: >
- Works best in codebases with CONTEXT.md domain documentation. Creates CONTEXT.md
- lazily when absent. Pairs with grill-with-docs for terminology refinement and
- code-refactoring for implementation.
+ Scans for deepening opportunities and reports them visually. Route the shared deep-module
+ vocabulary to codebase-design.
metadata:
- tags: architecture, refactoring, deep-modules, testability, locality, leverage
+ tags: deepening-opportunities, html-report, architecture-scan, seams, grilling
platforms: Claude, ChatGPT, Gemini, Codex
version: "1.0"
source: mattpocock/skills
+ upstream_commit: 3cca18b368ae95cdbdebbff572ccafa662551015
+ invocation: user-invoked
---
# Improve Codebase Architecture
- Surface architectural friction and propose **deepening opportunities** — refactors that turn shallow modules into deep ones. Goal: testability and AI-navigability.
+ Scan a codebase for deepening opportunities, present them as a visual HTML report, then grill through whichever one you pick. Use when the user wants architecture improvement candidates surfaced before choosing one. Triggers on: improve the architecture, find deepening opportunities, where should we refactor.
- ## Vocabulary (use these terms exactly)
+ This skill is imported from `mattpocock/skills` (MIT) and is **user-invoked** upstream.
- - **Module** — anything with an interface and implementation (function, class, package, slice)
- - **Interface** — everything a caller must know: types, invariants, error modes, ordering, config
- - **Depth** — leverage at the interface: much behavior behind a small interface. **Deep** = high leverage. **Shallow** = interface nearly as complex as the implementation
- - **Seam** — where an interface lives; a place behavior can be altered without editing in place
- - **Adapter** — a concrete thing satisfying an interface at a seam
- - **Leverage** — what callers get from depth
- - **Locality** — what maintainers get from depth: change, bugs, knowledge concentrated in one place
+ ## When to use this skill
- **Key principles:**
- - **Deletion test**: imagine deleting the module. If complexity vanishes, it was a pass-through. If complexity reappears across N callers, it was earning its keep.
- - **The interface is the test surface.**
- - **One adapter = hypothetical seam. Two adapters = real seam.**
+ - Scan a codebase for deepening opportunities, present them as a visual HTML report, then grill through whichever one you pick.
+ - Use when the user wants architecture improvement candidates surfaced before choosing one.
+ - Triggers on: improve the architecture, find deepening opportunities, where should we refactor.
- ## When to use this skill
+ ## Instructions
- - User wants architectural improvement opportunities
- - Codebase is hard to navigate or test
- - Modules feel tightly coupled or shallow
- - Refactoring would improve testability
+ ## Improve Codebase Architecture
- ## When not to use this skill
+ Surface architectural friction and propose **deepening opportunities**: refactors that turn shallow modules into deep ones. The aim is testability and AI-navigability.
- - Quick targeted refactors → use `code-refactoring`
- - Design review of a plan → use `grill-with-docs`
- - Implementation tickets → use `to-issues`
+ This command is _informed_ by the project's domain model and built on a shared design vocabulary:
- ## Process
+ - Call the Skill tool with "codebase-design" 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, and 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.
- ### 1. Explore
+ ### Process
- Read domain glossary (`CONTEXT.md`) and ADRs first. Then walk the codebase organically, noting friction:
+ #### 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.
+
+ Then spawn a sub-agent 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 modules?
- - Where are modules **shallow** — interface nearly as complex as the implementation?
- - Where have pure functions been extracted for testability, but real bugs hide in how they're called?
- - Where do tightly-coupled modules leak across seams?
- - Which parts are untested or hard to test through their current interface?
+ - Where are modules **shallow**, with an 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 suspected shallow modules.
+ 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
+ #### 2. Present candidates as an HTML report
- Numbered list of deepening opportunities. For each:
+ Write a self-contained HTML file to the OS temp directory so nothing lands in the repo. Resolve the temp dir from `$TMPDIR`, falling back to `/tmp` (or `%TEMP%` on Windows), and write to `<tmpdir>/architecture-review-<timestamp>.html` so each run gets a fresh file. Open it for the user (`xdg-open <path>` on Linux, `open <path>` on macOS, `start <path>` on Windows) and tell them the absolute path.
- - **Files** — which files/modules are involved
- - **Problem** — why the current architecture causes friction
- - **Solution** — plain English description of what would change
- - **Benefits** — in terms of locality, leverage, and test improvement
+ The report uses **Tailwind via CDN** for layout and styling, and **Mermaid via CDN** for diagrams where a graph/flow/sequence reliably communicates the structure. Mix Mermaid with hand-crafted CSS/SVG visuals: use Mermaid when relationships are graph-shaped (call graphs, dependencies, sequences), and hand-built divs/SVG when you want something more editorial (mass diagrams, cross-sections, collapse animations). Each candidate gets a **before/after visualisation**. Be visual.
- Use `CONTEXT.md` vocabulary for domain terms. Use the vocabulary above for architecture terms.
+ For each candidate, render a card with:
- **ADR conflicts**: if a candidate contradicts an ADR, only surface it when friction is real enough to warrant revisiting. Mark clearly: *"contradicts ADR-0007 — but worth reopening because…"*
+ - **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 diagram**: side-by-side, custom-drawn, illustrating the shallowness and the deepening
+ - **Recommendation strength**: one of `Strong`, `Worth exploring`, `Speculative`, rendered as a badge
- Ask: "Which of these would you like to explore?" — do NOT propose interfaces yet.
+ End the report with a **Top recommendation** section: which candidate you'd tackle first and why.
- ### 3. Grilling loop
+ **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."
- Once user picks a candidate, drop into a grilling conversation. Walk the design tree: constraints, dependencies, module shape, what sits behind the seam, what tests survive.
+ **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.
- Side effects as decisions crystallize:
- - **New concept not in CONTEXT.md?** Add the term immediately
- - **Fuzzy term sharpened?** Update CONTEXT.md right there
- - **User rejects with a load-bearing reason?** Offer an ADR (only when a future explorer would need it to avoid re-suggesting the same thing)
+ See [HTML-REPORT.md](HTML-REPORT.md) for the full HTML scaffold, diagram patterns, and styling guidance.
- ## Instructions
- 1. Identify the task trigger and expected output.
- 2. Follow the workflow steps in this skill from top to bottom.
- 3. Validate outputs before moving to the next step.
- 4. Capture blockers and fallback path if any step fails.
+ Do NOT propose interfaces yet. After the file is written, ask the user: "Which of these would you like to explore?"
+ #### 3. Grilling loop
+
+ Once the user picks a candidate, call the Skill tool with "grilling" 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; call the Skill tool with "domain-modeling" 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?** Call the Skill tool with "codebase-design" and use its design-it-twice parallel sub-agent pattern.
+
## Examples
- - Example: Apply this skill to a small scope first, then scale to full scope after validation passes.
+ - Apply this skill to one narrow scope first, confirm the output matches the shape described above, then widen to the full task.
+ - When a step needs a fact from the repository or the environment, look it up instead of asking the user for it.
+
## Best practices
- - Keep outputs deterministic and auditable.
- - Prefer small reversible changes over broad risky edits.
- - Record assumptions explicitly.
+ - Keep the upstream procedure intact; record deviations explicitly instead of silently improvising.
+ - Stop and hand control back to the user at every decision point this skill marks as theirs.
+ - Prefer small reversible changes, and state assumptions rather than burying them.
+
## References
+
+ - Upstream skill: `mattpocock/skills` `skills/engineering/improve-codebase-architecture/SKILL.md` (commit `3cca18b`, MIT)
+ - Companion doc: [references/HTML-REPORT.md](references/HTML-REPORT.md)
- Project standards: `.agent-skills/skill-standardization/SKILL.md`
- Validator script: `.agent-skills/skill-standardization/scripts/validate_skill.sh`