brownfield

name	brownfield
description	Discover and map an existing codebase before planning or changing it. Add --seams "<goal>" to also rank the safest cut-points for that goal.
argument-hint	[optional-focus-path-or-goal] [--seams "<goal>"]
context	fork
agent	planner

Brownfield Discovery

Use /brownfield in existing repositories before substantial planning, improvements, refactors, or bug work. The goal is to build a factual map of the current system so agents respect the codebase instead of inventing a parallel architecture.

This skill does not change production code.

Ultracode tip: Mapping an unknown codebase is the canonical fan-out task, so run /effort ultracode before this phase — broad parallel coverage plus adversarial verification produces better maps. Drop back to /effort high before the execution phases (/auto, /implement).

---

Usage

/brownfield
/brownfield backend/src
/brownfield "map auth and billing before adding team invites"
/brownfield --for "add team invites"          # lean maps scoped to a change goal
/brownfield --seams "add team invites"        # map, then rank the safest cut-points for this goal
/brownfield --full                            # LLM essays + CI/flag/perf + evaluator scoring

--seams "<goal>" is the single entry point for seam analysis: it runs the normal discovery, then runs the /seam-finder stage for <goal> and writes specs/brownfield/seams-<goal>.md. (/seam-finder remains directly invokable as a power-user stage, but you don't need to call it separately.)

Default /brownfield is intentionally lean and DeepWiki-first: build the deterministic graph/wiki, write deterministic short maps (no LLM essays), refresh nav indexes, and stop. Use --full for LLM-enriched essays, migration audits, CI/flag/perf inventory, or formal discovery scoring. Use --for "<goal>" to goal-scope the lean maps + optional seam ranking.

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Outputs

Write these files:

File	Purpose
specs/brownfield/code-graph.json	Deterministic dependency graph produced by /code-map
specs/brownfield/code-graph.meta.json	Producer, language counts, scan warnings, timestamp
specs/brownfield/wiki/WIKI.md + wiki/pages/*.md	Committed DeepWiki-style repo guide: module pages, Mermaid diagrams, source citations, and page index. Future code changes read this first.
specs/brownfield/symbol-map.md	Agent navigation map with symbols and line ranges for precise Read(offset, limit) slicing
specs/brownfield/codebase-map.md	Lean (default): deterministic inventory from nav-brownfield-maps.js. --full: optional LLM enrichment. Wiki is the main orientation artifact.
specs/brownfield/dependency-graph.md	Mermaid render of file/module-level edges
specs/brownfield/coupling-report.md	Fan-in, fan-out, cycles, hubs, unstable modules
specs/brownfield/architecture-map.md	Lean: deterministic hubs/layers/edges stub. --full: LLM narrative citing graph evidence
specs/brownfield/test-map.md	Lean: test paths from graph. --full: commands, coverage, flake notes
specs/brownfield/risk-map.md	Lean: keyword + coupling risks. --full: domain/security narrative
specs/brownfield/change-strategy.md	Lean: lane table + context-first steps. --full: richer strategy
specs/brownfield/ci-map.md, flag-inventory.md, perf-baseline.json	--full only: CI alignment, feature flags, and latency baseline

---

Step 1 — Inventory the Repo

Discover facts, not guesses:

• Languages and frameworks
• Package managers and lockfiles
• App entry points
• Test/build/lint/typecheck commands
• Runtime services and Docker/compose files
• Environment/config files
• CI workflows
• Database migrations or schema files
• Public API route definitions
• Frontend routes/screens

Use rg, find, package manifests, config files, and existing docs. Prefer primary repo evidence over assumptions.

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Step 1.5 — Build the Dependency Graph (delegate to /code-map)

Run the /code-map skill (.claude/skills/code-map/SKILL.md) — its Steps 1–3 are the single source of truth for producer detection (AST indexer → Understand-Anything import → regex fallback), the exact commands, and the rendering of symbol-map.md, dependency-graph.md, and coupling-report.md. Do not restate or improvise those commands here; if anything in this skill disagrees with code-map's SKILL.md, code-map wins.

Expected artifacts under specs/brownfield/ when it completes: code-graph.json (+ .meta.json), symbol-map.md, skeletons/ (god files only), dependency-graph.md, coupling-report.md, and wiki/WIKI.md + pages.

If the graph is empty or has only warnings, stop and report. Do not invent architecture from filenames. When the AST producer ran, treat symbol-map.md and skeletons/ as the navigation layer: read a single symbol with Read(offset=START, limit=END-START+1) instead of reading god files whole.

Step 1.6 — Deterministic lean maps + nav refresh (default)

Always run after a successful code-map (seconds, no LLM):

# Optional goal from --for "..." or the brownfield argument when it is a phrase
node .claude/scripts/nav-brownfield-maps.js --root . --goal "<goal-or-empty>"
node .claude/scripts/nav-query.js refresh

This writes/refreshes: lean codebase-map.md, architecture-map.md, test-map.md, risk-map.md, change-strategy.md, TF-IDF index, graph inverted index, co-change, concept pages.

Lean mode stops after Step 1.6 + Step 6 (glossary) + Gate — skip LLM Steps 2–5 unless --full or the user explicitly asked for narrative maps.

When a goal is present, also run:

node .claude/scripts/nav-query.js pack --diff --budget 1600 "<goal>"

and attach the pack summary to the human gate.

---

Step 2 — Map Architecture (--full only for LLM narrative)

In lean mode, keep the deterministic architecture-map.md from Step 1.6. Do not regenerate with an LLM.

In --full, expand architecture-map.md as a short companion to the wiki:

• Major modules and their responsibilities — cite specific edges from code-graph.json
• Public interfaces for each major module — use the graph symbols list where available
• Data flow through the system — follow imports / calls chains
• External integrations — cite ext:* targets from the graph where available
• Persistence boundaries
• Auth/session boundaries
• Existing layering conventions — confirm with directional fan-in/fan-out from coupling-report.md
• Deep modules worth preserving — high fan-in and low instability
• Shallow/pass-through modules that may be refactor candidates — high instability and little domain logic

Every "module X depends on Y" claim must reference graph evidence, preferably an edge with file:line evidence. Do not redesign the system. Capture what exists.

---

Step 3 — Map Tests (--full only for deep inventory)

In lean mode, keep the deterministic test-map.md from Step 1.6.

In --full, expand test-map.md with:

• Test frameworks and commands
• Unit/integration/e2e locations
• Which public interfaces are covered
• Which critical public interfaces lack tests
• Known slow/flaky tests if discoverable
• Whether tests isolate env/config correctly

If commands are obvious and safe, run lightweight discovery commands such as npm test -- --help, pytest --collect-only, or package script listing. Do not run expensive test suites unless the user asked.

---

Step 3.5 — Optional Full Inventory (--full only)

Skip this section in default lean mode. In --full, run the deterministic CI and flag inventory scripts:

node .claude/scripts/ci-ingest.js --root .     # → specs/brownfield/ci-map.md
node .claude/scripts/flag-scan.js --root .     # → specs/brownfield/flag-inventory.md

If the app is runnable (manifest has evaluation.api_base_url and evaluation.health_check, and the stack is up), also capture the performance baseline:

node .claude/scripts/perf-baseline.js          # → specs/brownfield/perf-baseline.json
# after a change: node .claude/scripts/perf-baseline.js --compare   (exit 1 on p95 regression)

• ci-map.md extracts the test/lint/coverage commands the project's CI actually enforces, with an alignment section against the harness gates. Where CI and harness disagree (different linter, different coverage bar), surface the discrepancy in change-strategy.md — the stricter gate should win, and the choice belongs to the user.
• flag-inventory.md lists feature-flag usage (SDKs, FEATURE_* env gates, config flags) with references. Flags gate dark code paths: a change inside a flagged path needs the flag's production state known before the lane is chosen.

Both are heuristic extractions — spot-check anything load-bearing against the source files. If a script reports nothing (no CI config, no flags), note that in the relevant map; absence is itself a finding.

Step 3.6 — Modularity Review (--full only, gap G6)

The deterministic coupling-report.md says where the coupling is; it cannot say whether a high-fan-in module is a god module or a legitimate factory, or whether two similar files are real duplication. Add the inferential layer, grounded in the coupling data so it does not flag intentional patterns:

node .claude/scripts/modularity-pack.js     # → specs/brownfield/modularity-pack.md (+ .json)

Then spawn the modularity-reviewer agent (artifact/maintainability sensor — inferential) against the pack. It judges semantic duplication, misplaced responsibility, argument clumps, and cycles against the source, confirms which likely-legitimate hubs are genuinely fine, and writes specs/reviews/modularity-review.md + modularity-verdict.json. This is a maintainability sensor, not a gate — it informs change-strategy.md and prioritizes refactoring; it never blocks. Skip in lean mode.

Once the agent completes, record that a real review just ran (gap G19 — the drift-cadence staleness proxy that tells the next drift run which unstable hubs are new since this review):

node .claude/scripts/record-modularity-review.js

This writes/updates .claude/state/modularity-review-marker.json with {timestamp, unstableHubIds} — the current unstable-hub set at the moment this review ran. Skip only if it errors for lack of a code-graph (already handled loudly by the script itself).

---

Step 4 — Map Risks (--full only for deep narrative)

In lean mode, keep the deterministic risk-map.md from Step 1.6.

In --full, expand risk-map.md with:

Domain risks

• Auth, permissions, privacy, billing, payment, and security-sensitive paths
• Database migrations and irreversible data operations
• External APIs and side-effecting integrations
• Generated code or vendored code that should not be edited manually
• Areas where tests are weak or missing
• Code paths gated by feature flags (flag-inventory.md) — the inactive branch may be the production one

Structural risks

Read these from coupling-report.md and code-graph.json:

• Cycles — files inside strongly connected components; refactors across cycle boundaries need explicit approval.
• Hub modules without tests — high fan-in files without corresponding test coverage in test-map.md.
• Unstable hubs — fan_in >= 5 and instability >= 0.8.
• Orphan files — fan_in == 0 and not an entry point.

For each risk, include the evidence path or graph node id.

---

Step 5 — Recommend Change Strategy (--full only for deep narrative)

In lean mode, keep the deterministic change-strategy.md from Step 1.6 (already includes context-first steps).

In --full, expand change-strategy.md with:

• What qualifies for /vibe
• What should use /change (behavior change; --issue N for a tracked bug)
• What should use /refactor
• What requires /spec → /design → /auto
• What should require explicit human approval before touching

Include a short "first safe next steps" list.

When recommending /spec → /design → /auto for any cluster of work, note in the strategy that /auto parallelizes on two axes:

• Within a group: multi-story groups (≥ 2 stories) fan out into parallel teammates — see .claude/agents/generator.md Rule 2.
• Across groups: independent dependency groups run concurrently as group-orchestrators (up to 3 by default) — see Section 4B of .claude/skills/auto/SKILL.md.

This shapes how you cluster stories AND how you shape the dependency graph: clusters with truly independent stories get within-group parallelism, and independent dependency groups (backend vs frontend vs ingest, for example) get cross-group parallelism. Prefer designs that surface independence at both levels — group by integration boundary internally, and minimize cross-group Consumes: edges in the dependency graph.

If the requested work has a concrete goal, run seam analysis via /brownfield --seams "<goal>" (which runs the /seam-finder stage for you). Use seams-<goal>.md to choose whether the next lane should extend an existing seam, wrap a boundary, introduce an adapter, split a read/write path, or avoid a poor seam.

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Step 6 — Domain Glossary

Run the deterministic naming-cluster extraction before writing anything:

node .claude/scripts/naming-clusters.js

This writes specs/brownfield/naming-clusters.md — root nouns that recur across 2+ symbols in code-graph.json (e.g. Account appearing in AccountController, AccountRepository, AccountService), each with file evidence. Treat this as candidate terms to confirm, not a final glossary — judge each against the source before writing a definition. It only catches suffix-stripped symbol names, not terms embedded purely in prose or comments, so also add any other recurring domain terms you find in the source.

Create or update CONTEXT.md from the confirmed candidates:

# Context

## Terms

### Account
Definition meaningful to users/domain experts.

### User
Definition and how it differs from Account.

Do not fill CONTEXT.md with implementation details. Every codebase produces at least the naming-clusters evidence file, so create CONTEXT.md even if only 1-2 terms are confirmed — it is no longer purely optional.

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Gate

Before recommending implementation, present:

• What the system appears to be
• Highest-risk areas
• Existing test confidence
• Recommended lane for the requested work
• Any uncertainty that needs human confirmation

Do not proceed to code changes from /brownfield unless the user explicitly asks.

---

Phase Evaluation Gate (--full only)

In lean mode, do not spawn an evaluator just to score discovery prose. The deterministic graph/wiki and source citations are the gate. In --full, after all discovery artifacts are written, spawn the evaluator agent (artifact mode) to validate the brownfield analysis.

Agent invocation:

Spawn Agent with subagent_type="evaluator" and prompt:

• Phase: brownfield
• Artifacts: specs/brownfield/codebase-map.md, specs/brownfield/architecture-map.md, specs/brownfield/test-map.md, specs/brownfield/risk-map.md, specs/brownfield/coupling-report.md, specs/brownfield/code-graph.json (if exists)
• Upstream: null (verify against actual codebase instead)
• Rubric: Read .claude/templates/phase-eval-rubrics.json, key "brownfield"
• Iteration: 1 (increment on retry)
• Previous score: null (or previous iteration's weighted_average)
• Verification: Spot-check 3-5 modules claimed in architecture-map.md actually exist as directories/files. Verify test commands in test-map.md reference real test files.
• Write result to specs/reviews/phase-brownfield-eval.json

Ratchet loop (max 2 iterations):

1. If verdict is PASS — proceed to Human Gate with eval summary.
2. If verdict is FAIL — re-scan the areas with findings. Update the maps. Re-run evaluator.
3. Ratchet rule: weighted_average must be >= previous iteration. Revert on regression.
4. After 2 iterations — present best version with findings to human.

---

Human Gate

Human approval is required before proceeding to implementation.

Present the discovery maps with the quality summary:

• Wiki path: specs/brownfield/wiki/WIKI.md
• Any remaining warnings from the graph producer or, in --full, the evaluator
• Recommended change strategy

Ask: "Does this brownfield analysis look accurate? Approve to proceed, or flag areas that need re-scanning."

Do not proceed to code changes from /brownfield unless the user explicitly approves the discovery AND requests changes.

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Gotchas

• Do not invent architecture. If evidence is missing, say unknown.
• Do not create parallel implementations. Brownfield work modifies existing paths unless a story/design explicitly approves a replacement.
• Do not trust names alone. Confirm responsibilities from imports, tests, route wiring, and callers.
• Do not over-map the universe. Focus enough to guide safe future changes.
• Do not run destructive commands. Discovery is read-only except for writing brownfield docs and optional CONTEXT.md.