Vibe Perf Skill

Full-stack performance audit grounded in actual measurements. Measures every layer. Scores it. Compares to last run. Flags regressions. Shows fix plan by category. Writes all approved fixes automatically.

Runs in agent mode (Claude Code / Cursor). Requires filesystem access.

The principle this enforces

Performance problems that aren't measured are invisible. Performance problems that aren't tracked regress silently. Performance problems caught before deploy cost minutes to fix. Performance problems caught in production cost users and reputation.

Measure first. Fix second. Never the other way around.

Entry points

Entry point A — On demand

Triggered by: perf:, "performance audit", "this is slow", "optimize X"

Default scope: full project audit across all applicable layers. If user specifies scope ("perf: frontend only" / "perf: audit the Scout agent") — scope to that layer/module only. Go to Step 0.

Entry point B — After vibe-review flags perf

Triggered when vibe-review produces P1/P2 findings tagged as performance.

Read the review report. Scope to flagged files and layers only. Go to Step 0.

Entry point C — Pre-deploy gate

Triggered automatically before vibe-deploy runs.

Full audit — all layers. If any P0 perf finding exists, deploy is blocked. Go to Step 0.

Step 0 — Read project context

Read in this order:

1. vibe/ARCHITECTURE.md — stack, patterns, any perf thresholds defined
2. vibe/CODEBASE.md — section 1 (stack), section 2 (commands),

section 5 (routes), section 7 (components), section 8 (services)

1. CLAUDE.md — dev/build/test/run commands
2. vibe/perf/baseline.json — previous run data (if exists)

Detect applicable audit layers from stack:

Check for custom perf thresholds in ARCHITECTURE.md: Look for ## Performance or ## Perf thresholds section. If found — these override all default thresholds in Steps 1–4. If not found — apply the default thresholds defined per step.

Check for previous run:

mkdir -p vibe/perf
ls vibe/perf/baseline.json 2>/dev/null && echo "BASELINE EXISTS" || echo "FIRST RUN"

If baseline exists — comparison run. Load previous scores for delta calculation. If first run — establish baseline. No deltas. Note "first run" in report.

Step 1 — Frontend audit

Skip entirely if no frontend detected in CODEBASE.md.

1A — Lighthouse CI

# Install if not present
npm list -g @lhci/cli 2>/dev/null || npm install -g @lhci/cli

# Dev server must be running — start if not
curl -s http://localhost:3000 > /dev/null 2>&1 || \
  ([dev command from CLAUDE.md] & sleep 8)

# Run 3 times for reliable average
lhci autorun \
  --collect.url=http://localhost:3000 \
  --collect.numberOfRuns=3 \
  --upload.target=filesystem \
  --upload.outputDir=vibe/perf/lighthouse

Also test key routes beyond / — read routes from CODEBASE.md section 5. Run Lighthouse on the 3 most trafficked routes.

Default score thresholds:

1B — Bundle analysis

# Vite
npx vite-bundle-visualizer --json 2>/dev/null \
  > vibe/perf/bundle-analysis.json

# Next.js
ANALYZE=true npm run build 2>&1 | tee vibe/perf/bundle-build.log

# Webpack
npx webpack-bundle-analyzer stats.json --mode json 2>/dev/null \
  > vibe/perf/bundle-analysis.json

Bundle thresholds:

From bundle output, identify:

• Duplicate dependencies (same package, multiple versions)
• Large dependencies that could be lazy-loaded or replaced
• Missing route-level code splitting
• Unused exports being included in bundle

1C — Component render analysis

Read each component file from CODEBASE.md section 7. Check for:

• Missing React.memo on pure components receiving complex props
• Object/array literals created inline in JSX props (new reference every render)
• useEffect with missing or incorrect dependency arrays
• Large lists (> 50 items) without virtualisation
• Images without loading="lazy" or next/image optimisation
• Missing key props on mapped lists
• Waterfall data fetching (sequential awaits that could be Promise.all)

Step 2 — Backend audit

Skip entirely if no backend detected in CODEBASE.md.

2A — API endpoint analysis

Read all route/controller files from CODEBASE.md section 5.

For each endpoint, identify:

• No response caching on idempotent GET endpoints
• Synchronous calls to external APIs where async would unblock the thread
• Missing pagination — list endpoints returning unbounded results
• Response payload including unused fields (over-fetching)
• Auth checks happening after expensive operations (should be first)

Response time thresholds (estimated from code patterns):

2B — Database query analysis

# Check Prisma schema for missing indexes
cat prisma/schema.prisma 2>/dev/null

# Find N+1 patterns — DB calls inside loops
grep -rn "\.findMany\|\.find\|\.query\|\.execute\|SELECT" \
  --include="*.ts" --include="*.js" --include="*.py" \
  . | grep -v node_modules | grep -v ".test." | grep -v migrations

Read each service file that touches the database. Identify:

• DB queries inside for / while loops → N+1
• SELECT * where specific columns would do
• Missing LIMIT on queries that could return unbounded rows
• Filters on columns with no index
• Missing indexes on foreign key columns
• Multi-step writes not wrapped in a transaction
• Missing composite indexes on frequently joined columns

# Prisma — check foreign keys without @index
grep -A5 "@relation" prisma/schema.prisma 2>/dev/null | \
  grep -v "@@index\|@id\|@unique"

DB query thresholds:

Step 3 — Agentic performance audit

Skip entirely if no agent patterns detected in CODEBASE.md.

Read references/AGENTIC_PERF.md before this step.

3A — LLM call efficiency

Read all agent files from CODEBASE.md section 8. Identify:

Token waste patterns:

• System prompts > 2000 tokens without clear justification
• Full conversation history passed to sub-agents on every call
• Entire session state serialised into every LLM call
• No structured output (JSON schema) where it would halve token usage
• Same external data fetched multiple times across agent calls
• Verifier prompts duplicating the full task spec (send only rubric)

Latency patterns:

• Sequential LLM calls with no data dependency (could be parallel)
• No streaming on user-facing generation
• Retry logic without exponential backoff
• Sub-agent calls with no timeout

Token thresholds:

3B — Agent loop efficiency

Read orchestrator and state management files:

• State object grows unboundedly across iterations (no pruning)
• Full state object passed to sub-agents (should pass task slice only)
• No max iteration cap on the verification loop
• Completed sub-task results not cached for retry scenarios
• Session state not persisted — re-runs expensive extraction on each start

Step 4 — Infrastructure audit

Skip if no Dockerfile / docker-compose / deployment config found.

# Read all config files
cat Dockerfile 2>/dev/null
cat docker-compose.yml docker-compose.yaml 2>/dev/null
cat Procfile 2>/dev/null
cat gunicorn.conf.py 2>/dev/null

# Check for resource limits
grep -n "mem_limit\|cpus\|memory\|cpu_shares\|max-old-space" \
  docker-compose.yml docker-compose.yaml package.json 2>/dev/null

# Node heap setting
grep -rn "max.old.space" . | grep -v node_modules

Check for:

• No memory limits on containers
• No CPU limits on containers
• Node.js heap not sized (default 512mb may be insufficient)
• Python workers not configured for async workload
• Docker image > 500mb (cold start impact)
• No multi-stage build (dev dependencies shipped to production)
• No health check endpoint defined
• No connection pooling configured for DB

Step 5 — Score, compare, build fix plan

Read references/PERF_REPORT_TEMPLATE.md for full report format.

Score calculation:

Compare with baseline (if exists): Calculate delta per layer. Flag any layer down > 5 points as regression. Regressions are P1 minimum. Regressions that push a layer below P0 threshold are P0.

Build the fix plan — two categories:

Read references/FIX_RISK_GUIDE.md for full risk classification.

Category A — Safe (auto-write on approval):

• DB indexes, query LIMIT additions
• React.memo, useMemo, useCallback additions
• Image lazy loading, next/image migration
• Bundle code splitting configuration
• Exponential backoff on retry logic
• Docker memory/CPU limits
• Agent token trimming, structured output adoption
• Promise.all for independent async calls

Category B — Risky (individual approval per fix):

• DB query restructuring (touches production data flow)
• Agent token budget changes (affects output quality)
• Orchestrator state management changes
• API response shape changes (pagination = breaking change)
• Component splits (may break existing tests)

Present fix plan and wait for approval. See output format in Step 9 below.

Approval commands:

• approve A — write all Category A fixes
• approve B: [N] — approve one risky fix by number
• approve all — approve everything
• skip [N] — exclude a specific fix

Step 6 — Write approved fixes

Write in this order: infrastructure → backend → agentic → frontend.

For each fix:

1. Read the target file in full
2. Make the minimal change that addresses the finding
3. Add inline comment: # perf: [what fixed] — vibe-perf [date]
4. Run verification immediately after:

# After DB index — check query plan
# After bundle change — rebuild and measure new size
# After component change — confirm no test failures
[test command from CLAUDE.md]

Never:

• Modify test files as part of a perf fix
• Remove functionality to gain performance
• Change public API interfaces without logging in DECISIONS.md
• Apply Category B fix without explicit approval

Step 7 — Update baseline and history

# Save this run as new baseline
cat > vibe/perf/baseline.json << 'EOF'
{
  "run_date": "[ISO date]",
  "run_number": [N],
  "trigger": "[on-demand|pre-deploy|post-review]",
  "scores": {
    "frontend": [N],
    "backend": [N],
    "agentic": [N],
    "infrastructure": [N],
    "overall": [N]
  },
  "findings": { "p0": [N], "p1": [N], "p2": [N], "regressions": [N] },
  "fixes_applied": [N],
  "fixes_pending": [N]
}
EOF

# Append to rolling history (create if not exists)
python3 -c "
import json, os
path = 'vibe/perf/history.json'
history = json.load(open(path)) if os.path.exists(path) else []
history.append(json.load(open('vibe/perf/baseline.json')))
json.dump(history, open(path, 'w'), indent=2)
"

Step 8 — Update vibe docs

vibe/TASKS.md — update "What just happened":

✅ Performance audit — [date] — Overall [N]/100 [↑/↓/→ vs last run]
   [N] fixes written · [N] pending manual review
   Report: vibe/perf/report-[date].md

vibe/reviews/backlog.md — add unfixed P1/P2 findings as perf backlog items. Resolve any previously logged perf items that were fixed in this run.

vibe/DECISIONS.md — log any Category B fix that changed an API shape or DB schema as a tech-choice entry with before/after detail.

Pre-deploy gate result (Entry C):

✅ PERF GATE PASSED — [N]/100 overall · 0 P0 findings · deploy unblocked
🔴 PERF GATE BLOCKED — [N] P0 findings must be resolved before deploy

Step 9 — Final report

Save to vibe/perf/report-[YYYY-MM-DD].md.

✅ vibe-perf complete — [Project Name] — [date]

SCORES
  Frontend:       [N]/100  [was N → delta]
  Backend:        [N]/100  [was N → delta]
  Agentic:        [N]/100  [was N → delta]
  Infrastructure: [N]/100  [was N → delta]
  Overall:        [N]/100  [was N → delta]

FINDINGS
  P0 critical: [N]    P1 warning: [N]    P2 note: [N]
  Regressions: [N]

FIXES WRITTEN:  [N] (Category A)
FIXES PENDING:  [N] (Category B — flagged in backlog)

NEXT PERF RUN WILL COMPARE AGAINST THIS BASELINE.
Full report: vibe/perf/report-[date].md
Baseline:    vibe/perf/baseline.json (run #[N])
History:     vibe/perf/history.json