codebase-modernizer

name	codebase-modernizer
description	Audit a stale, inherited, or messy codebase — deps, bugs, security, tests, CI, docs, UI/UX — then emit a phased, testable modernization plan. Read-only: plans upgrades, never applies them. Not for single-PR review, PRD-to-tasks, or UX-only audits.
license	MIT
effort	max
metadata	{"version":"1.2.2","author":"Luong NGUYEN <[e-mail]>","architecture":"orchestrator (baseline gate → parallel dimension audits → evidence report → phased sprint plan → validation)"}

Codebase Modernizer

For a codebase you are returning to after a long gap, or one that has drifted through many unoptimized changes. It audits the whole repo across every applicable dimension, then converts the findings into a phased, sprint-sized, testable plan for producing a better, up-to-date version.

Produces exactly two files in the target repo root:

File	Contents
MODERNIZATION_REPORT.md	Baseline evidence + every finding, severity-ranked, each citing path:line
MODERNIZATION_PLAN.md	Phases → sprints → tasks → milestones, every task closing named findings

Read-only contract

This skill never modifies source code, dependencies, lockfiles, or configuration — no tracked file's content changes. On a clean tree that is git diff --stat empty. On a stale, already-dirty tree, git status --porcelain and git diff after the run must match a snapshot taken before it (declared artifacts set aside). It runs read-only probes and writes the two report files above. Two kinds of new file may also appear, and both must be enumerated in the report's Artifacts section: a declared delegate artifact (CODE_REVIEW.md, from code-review mode review) and probe byproducts (build dirs some dependency probes create, such as obj/, .dart_tool/, target/, .gradle/). Nothing else.

• Dependency upgrades become planned tasks with migration steps — never npm update, ncu -u, cargo update, poetry update, or any equivalent. A blind bulk upgrade on a stale tree produces a broken build and an unreviewable diff, which is exactly what the plan exists to prevent.
• Refactors, dead-code removal, and test generation are planned, not applied. Applying them is the delegate skills' job, run later against the plan.
• Agent environment files (CLAUDE.md, AGENTS.md) are planned via /agent-config create or /agent-config update in the plan's Pre step — never created or rewritten during the audit.
• If the user asks mid-run to start fixing, finish the report and plan first, then hand off to the delegate skill named in that task.

Leading terms

Used throughout this skill and its references with these exact meanings:

• baseline-green — the recorded state where the project builds and its test suite runs to a known pass rate. Established in Phase 0; every P0–P4 task's acceptance criteria require it to hold. Pre is exempt when the baseline is RED — restore-green stays on P0 / Sprint 0.
• finding record — one normalized issue row with a stable finding ID (F-<DIM>-<NNN>, e.g. F-DEP-003). The report lists them; the plan's tasks close them by ID.
• Not Assessed — an explicit report verdict for a dimension that could not be checked (no tool, no UI, no network). Never replaced by a guess.
• fail-soft — probe whether a tool exists before using it; on absence, record Not Assessed with the reason and continue. A missing tool never aborts the run.
• upgrade wave — one batch of dependency upgrades that ships and is verified together: security patches → patch/minor batch → each major on its own.

Repo Sync Before Edits (mandatory)

Default: do not sync. This skill merges nothing and commits nothing — it writes two untracked report files. Rebasing mid-audit can pull in a year of upstream commits, invalidating every path:line citation and the recorded SHA. Audit the tree as you found it.

Sync only when the user asks for the reports committed or pushed. Then sync at the start of Phase 3, after the audit is recorded — and because HEAD moves, re-record the commit SHA and re-verify every citation still resolves. A citation that no longer resolves means the audit is stale: say so and re-run rather than publishing a report pointing at the wrong lines.

When syncing, sync the current branch with remote — stash first if the tree is not clean:

git stash push -u -m "pre-sync"   # only when `git status --porcelain` is non-empty
branch="$(git rev-parse --abbrev-ref HEAD)"
git fetch origin && git pull --rebase origin "$branch"
git stash pop                     # only if you stashed

If origin is missing, pull is unavailable, or rebase/stash conflicts occur, stop and ask the user before continuing. A dirty tree is common on a neglected repo — never discard uncommitted work.

Scope and branch selection

Resolve all nine branches in references/scope-detection.md before Phase 0 — target path, repo size, Agent-tool availability, Bash availability, Skill-tool availability, UI presence, app runnability, ecosystems, and any user dimension filter. Each is a real branch in the workflow, not a preference. Two of them change what is obtainable at all, so check them early:

• No Bash → no baseline is obtainable; every Phase 0 probe is a shell command. Record the whole baseline Not Assessed — no shell, audit only what static reading supports, and never fabricate a verdict.
• No UI detected → UI/UX dimensions are Not Assessed — no UI detected. Never invent UX findings.

Never assume the permissive side of a branch you did not check.

What this skill owns, and what it delegates

The finding-generators already exist. This skill's own contribution is dependency and runtime currency, the baseline gate, and the audit → plan bridge. Everything else is delegated.

Dim	Dimension	Audited by	Skip when
DEP	Dependency + runtime currency	this skill — references/dependency-audit.md, scripts/dep_scan.sh	no manifest found
BUG	Bugs, security holes, quality	invoke code-review mode review	never
PERF	Bottlenecks, leaks, algorithmic waste	invoke code-review mode perf	never
UX	Usability and UI flow	invoke dont-make-me-think	no UI detected
CLEAN	Readability vs Clean Code standards	inline — plan task runs code-review mode clean	never
DEAD	Dead code, duplication, slop, weak types	inline — plan task runs code-review mode cleanup	never
TEST	Untested branches and edge cases	inline — plan task runs test-coverage	never — an absent suite is itself a Critical finding
CI	Pipelines, pre-commit, quality gates	inline — plan task runs devops-pipeline	never
SEC	Secrets, dependency vulnerabilities	inline — plan task runs security-setup	never
DOCS	Docs drifted from code	inline — plan task runs doc-manager	never

Delegation policy — one rule: a delegate is invoked only if it changes no tracked file.

• Invoked (BUG, PERF, UX) — these never touch source. Normalize their output into finding records and record Path: delegated. code-review mode review writes its own CODE_REVIEW.md, a declared artifact that must be listed in the report's Artifacts section. Never let dont-make-me-think enter its Redesign Mode, which edits UI source files — ask for the usability review only and decline any offer to apply fixes.
• Inline (CLEAN, DEAD, TEST, CI, SEC, DOCS) — these delegates write, so invoking one during an audit would break the read-only contract. Never do it. Audit the dimension with its checklist in references/dimension-map.md, record Path: inline, and name that skill as the invocation in the plan task that does the work. Here inline is the expected path, not a degradation — do not report it as a limitation. The plan's Pre step likewise names /agent-config create|update and never runs it.

Read references/delegation-policy.md before Phase 2 for exact invocation args, artifact handling, and the Skill-tool-unavailable fallback (which is reduced depth).

Workflow

Phase 0 — Baseline (gate)

Read references/baseline.md and follow it. Establish and record, with evidence: build status, test command and pass rate, coverage if obtainable, lint status, CI presence and last result, runtime/toolchain versions in use.

A RED baseline (does not build, tests do not run, there is no suite, or the build could not be probed at all) does not stop the audit. Record Baseline: RED, continue, and make restoring baseline-green the plan's Sprint 0 — nothing downstream is verifiable without it.

Probes must not mutate tracked files. Snapshot git status --porcelain before and after Phase 0. Build and test commands can legitimately create build output, but any tracked file they change (a rewritten lockfile, a newly written test snapshot) is a finding, not an accepted side effect — report it and note that the probe was not reproducible. references/baseline.md gives the non-mutating form of each command.

When there is no test command, the baseline-green assertion every P0–P4 task carries falls back to the build: P0–P4 tasks before the P0 suite-creation task assert <build command> succeeds; every later P0–P4 task asserts the suite that task established. Do not apply this fallback to Pre.

Completion criteria: every row of the baseline table in references/baseline.md holds a recorded value or an explicit Not Assessed with a reason; the overall verdict is GREEN, AMBER, or RED; every value cites the command that produced it.

Phase 1 — Inventory and dimension selection

Detect stack, ecosystems, UI presence, repo size, and entry points. Produce the dimension worklist: each of the 10 dimensions marked audit or Not Assessed + reason. Confirm the worklist with the user only if the dimension filter is ambiguous; otherwise proceed.

Completion criteria: all 10 dimensions have a disposition; every ecosystem with a manifest is listed; repo-size branch and Agent-tool branch are both resolved and stated.

Phase 2 — Dimension audits

Read references/delegation-policy.md before invoking any delegated dimension — it holds the exact call for each, and the artifact handling that keeps the read-only contract intact.

Run DEP first — its output feeds the plan's upgrade waves and often explains findings in other dimensions. Then run the remaining audited dimensions, in parallel via agents/dimension-auditor.md when the size branch calls for subagents, otherwise inline.

• DEP uses agents/dependency-auditor.md and references/dependency-audit.md, one invocation per ecosystem. All DEP findings share the F-DEP- prefix, so allocate each ecosystem a distinct id_start (1, 101, 201, …) before spawning them; gaps in the numbering are fine, collisions are not.
• All other dimensions use agents/dimension-auditor.md with that dimension's row from references/dimension-map.md. Each has its own prefix and numbers from 1, so they need no ID coordination.
• No-fabrication rule: every finding record cites path:line (or a manifest entry and version for DEP), or it is dropped. A dimension that produced nothing citable is Not Assessed, not "no issues found".

Completion criteria: every dimension marked audit in Phase 1 returned either ≥ 1 finding record or an explicit "clean — checked X, found nothing" with the checks named; zero finding records lack evidence; finding IDs are unique and follow F-<DIM>-<NNN>.

Phase 3 — Write MODERNIZATION_REPORT.md

Merge all finding records into MODERNIZATION_REPORT.md using references/report-template.md. Rank by severity: Critical → High → Medium → Low.

Deduplicate before writing. Two dimensions reporting the same path:line produce one counted row, kept by whichever dimension appears earlier in the delegate table above. Follow the deduplication rule in references/report-template.md — it is what keeps the Summary counts equal to the number of rows.

Completion criteria: the file exists at the repo root; it contains the baseline table, a dimension coverage table showing all 10 dispositions, and the full finding table; every finding has ID, dimension, severity, evidence, and fix direction; the counts in the summary equal the rows in the table.

Phase 4 — Write MODERNIZATION_PLAN.md

Spawn agents/plan-architect.md with the report path (or run it inline when the Agent tool is unavailable). It writes MODERNIZATION_PLAN.md from references/plan-template.md, using the fixed skeleton (unconditional Pre, then P0–P4 — do not rename or renumber P0–P4):

Phase	Goal	Milestone
Pre Agent environment	env an AI agent can use autonomously; CLAUDE.md / AGENTS.md created or improved	ME — both files exist (create or update via planned /agent-config); recorded commands documented
P0 Stabilize	build green, tests runnable, lockfile committed, CI running	M0 — baseline-green reproducible in CI
P1 Secure & Patch	vulnerabilities closed, security patch + patch/minor upgrade waves	M1 — zero known High/Critical vulns; patch/minor current
P2 Modernize	each major dependency bump and runtime/toolchain upgrade, one task each	M2 — every major current or deferred with written rationale
P3 Clean & Harden	dead code, duplication, weak types, test coverage to target	M3 — coverage target met; duplication below stated threshold
P4 Polish	UI/UX, performance, docs alignment	M4 — UX findings closed; perf budget met; docs match code

Phases split into sprints. Every task uses the tasks-generator task format so the plan interoperates with that skill, plus a Closes: line naming finding IDs.

Completion criteria: Pre — Agent environment is present and ordered before P0, with create vs update of CLAUDE.md and AGENTS.md matching file presence and /agent-config named not run; every Critical and High finding is closed by ≥ 1 task; every task has ≥ 2 testable acceptance criteria; every P0–P4 task asserts baseline-green still holds (Pre is exempt when the baseline is RED — Pre ACs are install/run notes plus create-or-update of CLAUDE.md/AGENTS.md); task IDs follow Task Pre.<index> then Task <sprint>.<index>; the dependency table references only task IDs that exist; no circular dependencies; the critical path is stated explicitly; Pre and each of P0–P4 have a milestone with a measurable exit condition.

Phase 5 — Validation pass

Spawn agents/plan-validator.md with fresh context, giving it both output files and the repo. It verifies evidence citations resolve, severities are defensible, no finding is orphaned, no task invents work not traceable to a finding or a milestone, and the stated critical path is actually the longest chain in the dependency table.

Apply its corrections, then re-run the validator — maximum 2 rounds. Anything still open after round 2 goes into the report's Limitations with a reason rather than looping further.

Completion criteria: the validator has run at least twice when round 1 returned any must-fix; zero unresolved must-fix items remain, or each survivor is recorded in Limitations with a reason.

Step Completion Reports

After each phase, emit:

◆ [Phase Name] (phase N of 5 — [context])
··································································
  [Check 1]:          √ pass
  [Check 2]:          × fail — [reason]
  [Criteria]:         √ N/M met
  ____________________________
  Result:             PASS | FAIL | PARTIAL

Per-phase check names:

• Baseline: Build probed, Tests probed, Coverage probed, CI probed, Verdict recorded
• Inventory: Stack detected, Ecosystems listed, UI branch resolved, Worklist complete
• Audits: DEP complete, Delegated dims complete, Evidence cited, IDs unique
• Report: File written, Coverage table complete, Counts reconcile
• Plan: All Critical/High closed, Task format valid, No circular deps, Critical path stated, Milestones measurable
• Validation: Citations resolve, No orphan findings, Must-fix count 0

Never report PASS while a phase completion criterion, required output file, or safety guardrail is unresolved.

Acceptance Criteria

The run is successful only if all hold:

• MODERNIZATION_REPORT.md and MODERNIZATION_PLAN.md both exist at the target repo root.
• No tracked file's content changed relative to the pre-run snapshot. On a clean tree, git diff --stat is empty. On a stale already-dirty tree, git status --porcelain and git diff match the snapshot taken before the run (declared artifacts set aside). This is the promise that matters: no source, manifest, lockfile, hook, workflow, test, or docs file was modified by the audit.
• Every new file in git status --short is either one of the two reports, a declared delegate artifact (CODE_REVIEW.md), or a probe byproduct listed in the report's Artifacts section. Anything else is a contract breach.
• The baseline table is complete with a GREEN | AMBER | RED verdict and per-row evidence.
• All 10 dimensions appear in the coverage table with Audited or Not Assessed + reason.
• Every finding record has a unique F-<DIM>-<NNN> ID, a severity, and path:line evidence (or manifest+version for DEP).
• Every Critical and High finding is closed by at least one task in the plan.
• The plan starts with the Agent-environment pre-step, then P0–P4, each with ≥ 1 sprint and a measurable milestone. Pre is present whether CLAUDE.md / AGENTS.md already exist (update) or not (create). /agent-config is named, never invoked.
• Every task has ≥ 2 testable acceptance criteria, explicit Dependencies, an effort estimate, and a Closes: line. P0–P4 tasks include a baseline-green assertion. Pre is exempt when the baseline is RED (install/run notes plus create-or-update of CLAUDE.md/AGENTS.md).
• The dependency table has no broken task IDs and no cycles; the critical path is stated.

If any criterion fails, report it as a FAIL row in the Step Completion Report and do not claim success.

Expected Output

Target: /path/to/repo
Baseline: AMBER — builds; 41/58 tests pass; no coverage tool; CI absent
Dimensions: 8 audited, 2 Not Assessed (UX — no UI detected; PERF — out of requested scope)
Findings: 3 critical, 11 high, 24 medium, 9 low
Outputs: MODERNIZATION_REPORT.md, MODERNIZATION_PLAN.md
Plan: Pre + P0–P4, 10 sprints, 50 tasks — critical path Pre.1 → Pre.2 → 0.1 → 2.4
Validation: plan-validator PASS, 0 must-fix
Source files changed: 0

Edge Cases

• Not a git repo — skip Repo Sync, state it in the report, still write both files.
• Monorepo — scripts/dep_scan.sh probes the repo root only; re-run it once per package directory and merge the results, one ecosystem row and id_start block per package. Never accept "Ecosystems detected: none" while nested manifests exist. Scope other dimensions to the packages the user names, or all of them if unspecified.
• No manifest at all (shell scripts, plain HTML) — DEP is Not Assessed — no manifest; the plan drops P2 to a single "no dependency surface" note rather than inventing upgrade tasks.
• No network — dependency latest versions are unobtainable; record installed versions only and mark currency Not Assessed — offline. Never guess a latest version.
• Baseline RED — audit continues; the plan's Sprint 0 is "restore baseline-green" and every later task depends on it.
• Existing report files — back them up as MODERNIZATION_REPORT_backup_YYYY_MM_DD_HHMMSS.md before overwriting.
• Huge repo (> 2000 source files) — audit by subsystem in priority order, cap the file set per dimension, and state in Limitations exactly what was not scanned. Never silently truncate.
• User asks to apply fixes — handled by the Read-only contract above: finish both files first, then hand off.

Reference files

• references/scope-detection.md — the nine scope branches, detection, and resolution order.
• references/delegation-policy.md — invocation args, artifact handling, and fallbacks per path.
• references/baseline.md — Phase 0 probe protocol per stack, and the baseline evidence table.
• references/dependency-audit.md — per-ecosystem fail-soft probes, classification schema, upgrade wave rules, and migration-guide lookup for majors.
• references/dimension-map.md — the 10 dimensions: inline checklist, severity rubric, skip rules.
• references/report-template.md — MODERNIZATION_REPORT.md structure and the deduplication rule.
• references/plan-template.md — MODERNIZATION_PLAN.md structure and task format.
• scripts/dep_scan.sh — read-only ecosystem and dependency probe; prints a markdown summary.

Agents (spawn with the Agent tool; run inline if unavailable):

• agents/dependency-auditor.md — DEP dimension.
• agents/dimension-auditor.md — one delegated dimension per invocation.
• agents/plan-architect.md — report → MODERNIZATION_PLAN.md.
• agents/plan-validator.md — fresh-context validation of both outputs.