bundle-build-audit

name	bundle-build-audit
description	Audit build pipeline and bundle output (static-first with optional --with-stats enrichment). Checks configuration, composition, hygiene, and performance with optional implementation plan.
trigger	/bundle-build-audit

/bundle-build-audit

Audit a TypeScript frontend's build pipeline and bundle output against an opinionated baseline organised in four layers — build configuration, bundle composition and size, asset and dependency hygiene, build performance — preceded by a diagnostic snapshot. Then offer to generate an implementation plan for the gaps.

The default mental model is TypeScript and React. The skill works across Vite, Next.js (App Router and Pages Router), Remix, Create React App, plain Webpack, plain Rollup, and Turbopack. Parcel and direct esbuild app builds are out of scope.

Static-first design with optional stats enrichment

This skill is read-only and never executes the build. Two modes:

• Static (default). Read configuration files (vite.config.*, next.config.*, webpack.config.*, rollup.config.*, tsconfig.json), package.json, lockfiles, .gitignore, and continuous-integration workflow files. Bundle-composition and size checks degrade to "configured to do X" — there are no concrete numbers.
• Static plus opt-in --with-stats. When the flag is passed and a recognisable bundle-stats artefact exists at the expected path (dist/stats.json, .next/analyze/*.html, build/bundle-stats.json, dist/stats.html from rollup-plugin-visualizer, or bundle-stats.json from webpack-bundle-analyzer), the skill reads it and uses real numbers for size, composition, and per-chunk checks.

The skill never runs the build itself. Running npm run build (or equivalent) is the responsibility of the user or a separate fix-and-validate skill — keeping this audit fully read-only is what makes it safe to run in any working tree at any time.

Usage

/bundle-build-audit                                 # default: concise Top 5 + full report saved + ask about plan
/bundle-build-audit --worktree                          # create an isolated Git worktree, then run the audit there
/bundle-build-audit --learn                         # mid-level engineer teaching mode (detailed explanations + file/line examples)
/bundle-build-audit --teach                         # alias for --learn
/bundle-build-audit --with-stats                    # static plus enrichment from existing stats artefact
/bundle-build-audit --stats-path=path/to/stats.json # override the auto-detected stats artefact location
/bundle-build-audit --threshold-initial-bundle=300kb   # override default 250kb (gzipped)
/bundle-build-audit --threshold-total-bundle=1.5mb     # override default 1mb (gzipped)
/bundle-build-audit --threshold-build-time=90s         # override default 60s (clean build)
/bundle-build-audit --threshold-incremental-build-time=15s  # override default 10s

💡 Pro tip: Add --worktree to run this audit in an isolated Git worktree.

Threshold values accept human-friendly units: kb, mb, gb for sizes (interpreted as base-2 kilobytes, etc.); s, ms, m for time. The skill never accepts --apply.

The defaults baked into the skill are the recommended baseline for a typical modern React and TypeScript application. Threshold flags exist as an escape hatch for projects with deliberately different sensibilities; the canonical path to evolving the defaults themselves is /system-self-improve.

💡 Pro tip: Run /preflight --audit=bundle-build first to detect — and optionally install — the development dependency that makes --with-stats useful (a bundle analyser matching your build tool: webpack-bundle-analyzer, @next/bundle-analyzer, rollup-plugin-visualizer, or vite-bundle-visualizer). Skip if you already know the tooling is wired up.

The opinionated baseline

A check resolves to one of four statuses:

• present — the invariant holds.
• partial — most signals resolve, with a small number of exceptions.
• missing — a structural prerequisite is absent.
• violation — the audit identified concrete configuration or output that breaks the invariant.

Layer 0 is informational only and has no status.

Layer 0 — Diagnostic snapshot (always written, no pass/fail)

• Detected build tool and version (Vite 5.x, Next.js 14 App Router, Webpack 5, Rollup 4, Turbopack).
• Detected meta-framework (Next.js, Remix, Vite-React, Create React App, plain Vite, plain Webpack).
• Entry points and discovered route count when discoverable from the framework's conventions.
• Total bundle size and per-chunk breakdown — only when a stats artefact is available; otherwise "not measured".
• Top 10 largest dependencies in the bundle — only when stats are available.
• Browserslist resolved targets (run npx browserslist mentally — the skill reads the configuration and does not execute).
• Source-map mode: none, inline, separate file, or hidden with header.
• Build cache state: enabled, configured, and the location it points at.

Layer 1 — Build configuration soundness

Check	Expectation	Violation signal
Build tool present and pinned	A build tool is installed and its version is pinned in package.json (no ^ or ~ on the build tool itself).	Build tool missing, or pinned with a caret or tilde range.
Browserslist explicit	A browserslist field exists in package.json, or a .browserslistrc file is present.	No browserslist configuration anywhere.
Production mode enforced	The build script invokes the framework's production-build command and the continuous-integration workflow runs it with NODE_ENV=production.	NODE_ENV not set, or the build script invokes a development command.
Source maps configured deliberately	Production builds emit source maps in an explicitly chosen mode (hidden, separate file, or fully off).	No source-map configuration whatsoever; the build tool's default is silently in use.
Build output ignored from git	The build output directory (dist/, .next/, build/, out/) is in .gitignore.	Build output committed or not ignored.
Production dependencies separated	No development-only packages (build tools, type definitions, test runners, linters, formatters, Storybook) appear in dependencies.	Development packages in dependencies.
Deterministic build	The build script does not depend on environment-specific flags or interactive input.	Scripts containing --watch, interactive prompts, non-deterministic timestamps in output filenames.

Layer 2 — Bundle composition and size

Defaults in parentheses; every threshold overridable via flags. Checks marked stats-required report partial (with a "stats artefact not present" gap) when running without --with-stats.

Check	Expectation	Violation signal
Initial bundle size budget (stats-required)	The initial JavaScript payload (entry chunk plus shared chunks loaded on first paint) is under the threshold (default 250 kilobytes gzipped).	Initial payload exceeds the threshold.
Total bundle size budget (stats-required)	The full client-side JavaScript payload across all chunks is under the threshold (default 1 megabyte gzipped).	Total exceeds the threshold.
Route-level code splitting	The build splits per route or per page.	Single-bundle output, or the framework's automatic route-splitting has been turned off.
No duplicate dependencies	Each dependency appears exactly once in the bundle; React, React-DOM, and large utilities are not bundled twice.	Multiple copies detected in stats (when available); or multiple incompatible major versions in the lockfile.
Large-library hygiene	Large libraries are imported with named imports or per-method paths so tree-shaking can remove what isn't used.	Patterns like import _ from 'lodash', import moment from 'moment', import * as X from 'large-lib' in source.
Dynamic imports for heavy features	Heavy non-critical features (rich-text editors, charting libraries, code mirrors, video players, PDF renderers) are loaded with React.lazy or framework-equivalent dynamic imports.	Heavy libraries imported synchronously at the top level of an entry-reachable module.
No development-only code in production	No unguarded console.log, no React DevTools shim, no debug-only code paths reachable in production builds.	Such patterns present in source without an if (process.env.NODE_ENV !== 'production') guard, or detected in built output when stats are available.

Layer 3 — Asset and dependency hygiene

Check	Expectation	Violation signal
Image optimisation	Images use modern formats (WebP, AVIF) where the framework supports them. The framework's image primitive is used (next/image for Next.js, <Image> from @unpic/react or vite-plugin-image-optimizer for Vite).	Multi-megabyte PNGs or JPEGs in public/; Next.js project not using next/image for content imagery.
Font handling	Fonts are subset, self-hosted (or via a CDN with font-display: swap), and preloaded for above-the-fold text.	Loading entire web-font families with no font-display; sourcing fonts from a script-blocking external host.
CSS extraction	CSS is extracted into separate files in production builds, except for above-the-fold critical CSS.	CSS-in-JS configuration that ships styles inside JS chunks unconditionally without extraction.
Static assets cacheable	Build output produces hashed filenames (main.[hash].js) so long-cache headers can be set safely.	Filenames without content hashes.
No vendored dependencies	No copies of third-party packages live under src/ or vendor/.	Files matching the signature of a known package present in src/.
sideEffects field declared	package.json has a sideEffects field set to false (or an array of files known to have side effects), so tree-shaking can remove unused exports.	Field absent.
Bundle analyser available	A bundle-analysis tool is installed and runnable. Recognised: vite-bundle-visualizer, rollup-plugin-visualizer, @next/bundle-analyzer, webpack-bundle-analyzer.	None present.

Layer 4 — Build performance

Check	Expectation	Violation signal
Build cache enabled	The build tool's cache is enabled (Vite's dependency cache, Next.js .next/cache, Webpack cache: { type: 'filesystem' }, Turbopack defaults).	Cache disabled or configured to a discarded location.
TypeScript incremental mode	tsconfig.json has incremental: true, or the project uses composite project references.	Neither enabled.
Continuous-integration cache	The continuous-integration workflow caches the package-manager store and the build cache between runs.	No cache step in .github/workflows/*.yml (or equivalent), or the cache key is not derived from the lockfile hash.
Bundle-size budget enforced in continuous integration	A bundle-size check runs in continuous integration and fails the build when the budget is exceeded (size-limit, bundlewatch, @next/bundle-analyzer with thresholds, or equivalent).	No such step detected.
Build-time budget (stats-required)	Reported clean-build time is under the threshold (default 60 seconds), reported incremental rebuild time is under the threshold (default 10 seconds). Soft check — partial between threshold and 1.5 times threshold, violation above.	Measurements (when available from continuous-integration logs or local cache) exceed the thresholds.

What this skill does

1. Reads the knowledge graph when present. Soft dependency: if graphify-out/graph.json exists, the skill uses community structure to suggest cleavage planes for code-splitting in the implementation plan. If absent, the audit still runs in full — the only loss is some intelligence in the remediation suggestions.

2. Confirms a Node.js project with a recognised build tool. Detects the build tool from package.json dependencies and configuration files. If none of the supported build tools is detected, the skill stops and tells the user.

3. Detects the meta-framework for the diagnostic snapshot.

4. Locates a stats artefact when --with-stats is set. Searches the conventional paths for the detected build tool, plus any path passed via --stats-path. Records the path or the absence in the snapshot.

5. Writes Layer 0 — the diagnostic snapshot to .architect-audits/bundle-build-audit/snapshot.md and prepends the same content to findings.md.

6. Walks each check in the active layer list, applying any --include, --exclude, and threshold overrides. Stats-required checks emit partial with a clear "no stats artefact" gap when running without enrichment.

7. Writes phase 1 outputs to .architect-audits/bundle-build-audit/:

   • findings.md — diagnostic snapshot followed by check results, grouped by layer.
   • findings.json — machine-readable.
   • snapshot.md — diagnostic snapshot on its own.
   • metadata.json — skill version, run timestamp, Graphify revision hash (when present), build tool, framework, stats artefact path (or null), applied thresholds, applied filters.

8. Phase 2 — offers to plan the gaps. Summarises the findings in chat and asks the user a single yes-or-no question:

   "Generate an implementation plan for the bundle and build gaps? (yes/no)"

   On yes, writes .architect-audits/bundle-build-audit/implementation-plan.md describing exactly which configuration entries to add, which dependencies to swap, which dynamic imports to introduce, and which continuous-integration steps to add — ordered by layer and then by severity. The plan does not modify any project files.

   On no, exits cleanly.

Implementation steps

Step 1 — Confirm the prerequisites

test -f package.json || { echo "bundle-build-audit: no package.json detected. This skill currently supports Node.js frontend projects only."; exit 1; }

Detect the build tool:

• vite dependency → Vite.
• next dependency → Next.js (with App Router or Pages Router based on directory layout).
• @remix-run/* dependency → Remix.
• react-scripts dependency → Create React App.
• webpack dependency with a webpack.config.* → plain Webpack.
• rollup dependency with a rollup.config.* → plain Rollup.
• @vercel/turbopack or Next.js with Turbopack opted in → Turbopack.

If none match, stop and tell the user the skill currently supports the listed tools only.

Step 2 — Locate the stats artefact (if --with-stats)

For each known build tool, check the conventional path:

• Vite with rollup-plugin-visualizer: dist/stats.html or dist/stats.json.
• Next.js with @next/bundle-analyzer: .next/analyze/client.html, .next/analyze/server.html.
• Webpack with webpack-bundle-analyzer: bundle-stats.json at the project root, or dist/bundle-stats.json.
• Rollup with rollup-plugin-visualizer: dist/stats.html, dist/stats.json.

Honour --stats-path over the conventional locations.

If --with-stats is set but no artefact is found, continue running with stats-required checks degrading to partial and add a clear "no stats artefact found at " line to the snapshot. Also print to the chat and prepend to findings.md: "--with-stats was requested but no bundle-stats artefact is available. If you have not installed a bundle analyser, run /preflight --audit=bundle-build --install to install one matching your build tool. Otherwise run npm run build (or your project's equivalent with the analyser enabled) to produce the artefact, then re-run with --with-stats." Record recoveryHint: "/preflight --audit=bundle-build --install" on each stats-required check that degraded to partial in findings.json.

Step 3 — Build the diagnostic snapshot

Read configuration files and (when available) the stats artefact. Compute the items listed in Layer 0. Write snapshot.md and prepend the same content to findings.md.

Step 4 — Resolve each check

For each check in the active layer list, walk its detection logic. Use the same status taxonomy as the other audits (present, partial, missing, violation). Stats-required checks running without enrichment record partial with the gap "stats artefact not present; static signals indicate ".

Step 5 — Write phase 1 outputs

Create .architect-audits/bundle-build-audit/ if needed. Write findings.md, findings.json, snapshot.md, metadata.json. Overwrite previous runs of these four; preserve implementation-plan.md unless the user agrees to regenerate it.

Step 6 — Print the concise chat summary and offer phase 2

Print a human-first, scannable summary in the chat. Do not print the full layered findings — those are written to disk in Step 5. The chat output has exactly this shape:

1. Short header — audit name, timestamp, and a one-line summary of the codebase state.
2. Top 5 Highest-Leverage Recommendations — ordered by architectural principles: test philosophy, maintainability, risk reduction, velocity, long-term health. For fewer than five findings, print what exists. For each recommendation (numbered 1–5):
   • Title (one clear line).
   • Why it matters (explain the principle in 1–2 sentences).
   • Real consequences if ignored (honest downside for the team or project).
   • Smallest high-leverage fix (exact next step, effort level, and which files to touch).
   • At the end, add a lettered sub-list of concrete actions if useful (e.g. 2a, 2b) so the user can reply with "2b" or "1 and 3" to trigger implementation.
3. Bottom line: Full detailed audit report (layered findings, snapshot, metadata, implementation plan) → .architect-audits/bundle-build-audit/findings.md

When --learn or --teach is set, expand each recommendation into mid-level engineer teaching mode:

• For every item, explain as if teaching a mid-level engineer, pointing to specific files and line numbers from the current codebase.
• Use educational language: "Here's why this pattern bites teams in the long run…", "This is the exact mistake I see in most codebases at your stage…", "The fix is small but pays off huge because…".
• Include a short "What you'll learn from fixing this" section for each recommendation.
• Keep the numbered/lettered structure so the user can still reply with "2b" or "1 and 3".
• End with the same bottom-line link to the full report.

After printing, ask the single yes-or-no question: "Generate an implementation plan for the gaps identified above? (yes/no)" Do not proceed to phase 2 without an explicit affirmative.

Step 7 — Phase 2: generate the implementation plan

When the user agrees, build implementation-plan.md:

1. Header — repository name, baseline version, build tool, framework, stats source, timestamp, total counts per layer.
2. Layer 1 — build configuration plan: configuration snippets to add or change, with the exact file path.
3. Layer 2 — bundle composition and size plan: per violation, the offending pattern, the recommended replacement (named imports, dynamic imports, library swaps), and — when the Graphify graph is present — community-derived split planes for routes or feature folders.
4. Layer 3 — asset and dependency hygiene plan: per violation, the asset class, the recommended primitive (framework image component, font-loading approach), and the configuration change.
5. Layer 4 — build performance plan: continuous-integration cache step snippets, TypeScript configuration changes, bundle-size budget configuration.
6. Closing checklist — a flat checkbox list mirroring the gaps, suitable for pasting into a pull-request description.

The plan is descriptive, not executable. It does not install packages and it does not modify configuration files.

Findings file shape

findings.json:

{
  "skillVersion": "1.0.0",
  "runStartedAt": "2026-04-26T13:47:00Z",
  "runFinishedAt": "2026-04-26T13:47:11Z",
  "buildTool": "vite",
  "framework": "vite-react",
  "statsSource": "dist/stats.json",
  "thresholds": {
    "initialBundleBytesGzipped": 256000,
    "totalBundleBytesGzipped": 1048576,
    "buildTimeSeconds": 60,
    "incrementalBuildTimeSeconds": 10
  },
  "snapshot": {
    "buildTool": { "name": "vite", "version": "5.4.0" },
    "framework": "vite-react",
    "entryPoints": ["src/main.tsx"],
    "totalBundleBytesGzipped": 712000,
    "perChunk": [
      { "name": "main", "bytesGzipped": 184000, "modules": 421 }
    ],
    "topDependencies": [
      { "name": "react-dom", "bytesGzipped": 41000 }
    ],
    "browserslist": ["chrome >= 109", "firefox >= 115", "safari >= 16"],
    "sourceMapMode": "hidden",
    "buildCache": { "enabled": true, "location": "node_modules/.vite" }
  },
  "summary": {
    "buildConfiguration":         { "present": 5, "partial": 1, "missing": 1, "violation": 0 },
    "bundleCompositionAndSize":   { "present": 3, "partial": 2, "missing": 0, "violation": 2 },
    "assetAndDependencyHygiene":  { "present": 4, "partial": 0, "missing": 2, "violation": 1 },
    "buildPerformance":           { "present": 3, "partial": 1, "missing": 1, "violation": 0 }
  },
  "checks": [
    {
      "layer": "bundle-composition-and-size",
      "check": "large-library-hygiene",
      "status": "violation",
      "thresholdApplied": null,
      "evidence": [],
      "samples": [
        { "path": "src/utils/format.ts", "match": "import _ from 'lodash'" }
      ],
      "expectation": "Large libraries are imported with named imports or per-method paths so tree-shaking can remove what isn't used.",
      "gap": "lodash imported as default in 4 files; full library shipped to the client.",
      "remediation": "Replace with `import { debounce } from 'lodash-es'` (or per-method paths) and add lodash-es to dependencies if not already present."
    }
  ]
}

findings.md mirrors the same content in human-readable form, with the diagnostic snapshot at the top and one section per check, grouped by layer. snapshot.md contains only the snapshot. metadata.json carries the skill identity, timestamps, Graphify revision when present, and the configuration of the run.

Idempotency rules

• Re-running with no flags overwrites findings.md, findings.json, snapshot.md, and metadata.json in place.
• implementation-plan.md is preserved across runs unless the user agrees to regenerate it.
• Filter flags, threshold overrides, the --with-stats flag, and the resolved --stats-path are recorded in metadata.json so a partial run can be reproduced.

Failure modes and remediation

Symptom	Cause	Fix
no package.json detected	The skill is run outside a Node.js project root.	Change directory into the project root and re-run.
No supported build tool detected	The project uses Parcel, esbuild directly, or a custom build script.	Stop. Inform the user that the skill currently supports Vite, Next.js, Remix, Create React App, Webpack, Rollup, and Turbopack only.
--with-stats set but no stats artefact found	The user has not installed a bundle analyser, or has not run npm run build (or equivalent with the bundle analyser enabled) recently.	Continue running. Mark stats-required checks as partial with the gap "stats artefact not present at ". Recovery: run /preflight --audit=bundle-build --install to install a bundle analyser if missing, then run the build to produce the artefact and re-run with --with-stats.
Stats artefact present but unreadable	Corrupt or unrecognised format.	Treat the artefact as missing. Record the parse error in the snapshot. Continue with degraded checks.
Knowledge graph missing	/pre-audit-setup has not been run.	Continue. Record noGraphify: true in metadata.json. The implementation plan loses the community-derived split-plane suggestions; everything else is unaffected.
Multiple build tools detected	Both Webpack and Vite configured — possibly in a migration.	Pick the one referenced by the production build script in package.json. Mention the secondary tool in the snapshot.

What this skill explicitly does NOT do

• Run the build. The audit is fully read-only.
• Install any package or dependency.
• Create, modify, or delete any file outside .architect-audits/bundle-build-audit/.
• Modify configuration, source files, or continuous-integration workflows.
• Open pull requests or commit anything to git.
• Audit Parcel, raw esbuild, or custom build pipelines.
• Measure runtime performance. That is the responsibility of /performance-audit. This skill stops at the bytes shipped and the time taken to ship them.
• Make build-tool migration recommendations (Webpack to Vite, Pages Router to App Router). Migration is a project-shaping decision, not an audit finding.