ab-testing
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A/B Testing Platform for SaaS
Stack: Next.js 16 + Edge Middleware + GA4/GTM + Supabase + Rust-WASM (for stats) Why DIY?: Google Optimize sunset Sept 2023. GA4 has no native A/B testing.
Quick Start
// middleware.ts - Server-side assignment (no flicker)
import { NextResponse, type NextRequest } from 'next/server'
export function middleware(request: NextRequest) {
const response = NextResponse.next()
if (!request.cookies.get('exp_hero')) {
const variant = Math.random() < 0.5 ? 'A' : 'B'
response.cookies.set('exp_hero', variant, { maxAge: 60*60*24*30, path: '/' })
}
return response
}
// Track with GA4
window.dataLayer?.push({
event: 'experiment_view',
experiment_name: 'hero_test',
experiment_variant: variant
})
Architecture
┌─────────────────────────────────────────────────────────────────────┐
│ A/B TESTING FLOW │
├─────────────────────────────────────────────────────────────────────┤
│ │
│ 1. ASSIGN (Edge Middleware) │
│ ══════════════════════════ │
│ Request → Check cookie → Random assign → Set cookie → Response │
│ ✓ No flicker (server-side) ✓ Consistent (cookie-based) │
│ │
│ 2. RENDER │
│ ═════════ │
│ Server/Client Component → Read cookie → Show variant │
│ │
│ 3. TRACK (GTM + GA4) │
│ ════════════════════ │
│ dataLayer.push → GTM triggers → GA4 events with variant param │
│ │
│ 4. ANALYZE │
│ ═════════ │
│ GA4 Explorations OR Supabase + Rust-WASM Bayesian analysis │
│ │
│ 5. PERSONALIZE (Advanced) │
│ ═════════════════════════ │
│ Contextual bandit → Best variant per user segment │
│ │
└─────────────────────────────────────────────────────────────────────┘
Workflow
-
- Define experiment config (name, variants, weight, segment rules)
-
- Implement middleware assignment (see VARIANT-ASSIGNMENT.md)
-
- Wire up GTM tracking (experiment_view, conversions with variant param)
-
- Register
experiment_variantas Custom Dimension in GA4
- Register
-
- Collect data (minimum 2 weeks for weekly patterns)
-
- Analyze significance (see STATISTICAL-ANALYSIS.md)
-
- Roll out winner or iterate
Statistical Methods (Choose One)
| Method | Best For | Decision Output |
|---|---|---|
| Frequentist | Fixed sample, strict control | p-value < 0.05 → significant |
| Bayesian | Continuous monitoring, intuitive | P(B > A) = 96% → B likely better |
| Multi-Armed Bandit | Optimize during test | Auto-shift traffic to winner |
| Contextual Bandit | Personalization | Best variant per user segment |
Quick Bayesian (Beta-Binomial):
# A: 50/1000 conversions, B: 72/1000
import scipy.stats as stats
a_samples = stats.beta(51, 951).rvs(100000) # Beta(1+50, 1+950)
b_samples = stats.beta(73, 929).rvs(100000) # Beta(1+72, 1+928)
p_b_wins = (b_samples > a_samples).mean() # → ~0.96 (96%)
Full analysis guide: STATISTICAL-ANALYSIS.md
Key Patterns
Multiple Concurrent Experiments
// middleware.ts
const EXPERIMENTS = {
hero_cta: { weight: 0.5 },
pricing_layout: { weight: 0.5 },
signup_flow: { weight: 0.2 }, // 20% on new variant
}
for (const [name, config] of Object.entries(EXPERIMENTS)) {
if (!request.cookies.get(`exp_${name}`)) {
const variant = Math.random() < config.weight ? 'B' : 'A'
response.cookies.set(`exp_${name}`, variant, { maxAge: 2592000, path: '/' })
}
}
Phased Rollout
// Config stored in Supabase or Vercel Edge Config
const rolloutPhases = {
early_access: 0.1, // 10% new
public_beta: 0.5, // 50% new
general: 1.0 // 100% new (winner)
}
Tracking Conversions
// Include variant in ALL relevant events
window.dataLayer?.push({
event: 'sign_up',
method: 'google',
experiment_name: 'hero_cta',
experiment_variant: getCookie('exp_hero_cta'),
eventId: crypto.randomUUID() // De-duplication
})
When to Use Rust-WASM
| Use Case | Why Rust |
|---|---|
| Monte Carlo simulation (100k+ draws) | 10-100x faster than JS |
| Bayesian posterior computation | Numerical precision |
| Contextual bandit inference | Real-time ML at edge |
| Cross-platform consistency | Same logic in browser + server |
WASM is NOT needed for: Simple random assignment, cookie handling, event tracking
See: RUST-WASM.md
Anti-Patterns
| Don't | Why |
|---|---|
| Client-side variant assignment | Causes flicker, inconsistent |
| End test early ("B winning after 2 days!") | Random noise, not signal |
| Multiple changes in one variant | Can't isolate what worked |
| Overlapping tests on same element | Interaction effects confound |
| Skip sample size calculation | Under-powered = false negatives |
| Ignore segments | Winner overall may lose for key segment |
Validation Checklist
- No flicker on page load (verify in slow 3G)
- Cookie persists across sessions (check 30-day expiry)
- GTM Preview shows correct variant in dataLayer
- GA4 DebugView receives events with variant param
- Custom dimension
experiment_variantregistered in GA4 - ~50/50 split verified (check GA4 Realtime)
- Conversion events include variant attribution
Reference Index
By Task
| I need to... | Read |
|---|---|
| Implement variant assignment | VARIANT-ASSIGNMENT.md |
| Choose a statistical method | STATISTICAL-ANALYSIS.md |
| Set up GTM/GA4 tracking | GA4-GTM-TRACKING.md |
| Build admin dashboard | ADMIN-DASHBOARD.md |
| Add personalization/bandits | PERSONALIZATION.md |
| Optimize with Rust-WASM | RUST-WASM.md |
| Quick lookup (tools, formulas) | QUICK-REFERENCE.md |
By Topic
| Topic | Reference |
|---|---|
| Server-side assignment, multiple experiments, weighted splits | VARIANT-ASSIGNMENT.md |
| Frequentist vs Bayesian vs Bandits, sample size, pitfalls | STATISTICAL-ANALYSIS.md |
| GTM variables, GA4 events, BigQuery queries, debugging | GA4-GTM-TRACKING.md |
| Database schema, API routes, UI components, real-time updates | ADMIN-DASHBOARD.md |
| Segments, rules-based, Thompson sampling, contextual bandits | PERSONALIZATION.md |
| Rust setup, beta sampling, bandit implementation, Next.js integration | RUST-WASM.md |
| Tool recommendations, decision guide, formulas, cheat sheet | QUICK-REFERENCE.md |
<!-- tomevault:4.0:skill_md:2026-05-23 -->Source: danzam98/claude-skills-toolkit — distributed by TomeVault.
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- Static check
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- Author / version / license
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- Fluxly token estimate
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Profile is derived at build time from SKILL.md and install vectors. Subject to drift from author intent.
Heads up: 未限定 allowed-tools,默认拥有全部工具权限。
The current SKILL.md does not define a fixed output example. Quick Start
[ ] 1. Define experiment config (name, variants, weight, segment rules) [ ] 2. Implement middleware assignment (see VARIANT-ASSIGNMENT.md) [ ] 3. Wire up GTM tracking (experimentview, conversions with variant param)
Method · Best For · Decision Output Frequentist · Fixed sample, strict control · p-value < 0.05 → significant Bayesian · Continuous monitoring, intuitive · P(B > A) = 96% → B likely better
Phased Rollout
# A/B Testing Platform for SaaS
> **Stack**: Next.js 16 + Edge Middleware + GA4/GTM + Supabase + Rust-WASM (for stats)
> **Why DIY?**: Google Optimize sunset Sept 2023. GA4 has no native A/B testing.
## Quick Start
```tsx
// middleware.ts - Server-side assignment (no flicker)
import { NextResponse, type NextRequest } from 'next/server'
export function middleware(request: NextRequest) {
const response = NextResponse.next()
if (!request.cookies.get('exp_hero')) {
const variant = Math.random() < 0.5 ? 'A' : 'B'
response.cookies.set('exp_hero', variant, { maxAge: 60*60*24*30, path: '/' })
}
return response
}
```
```tsx
// Track with GA4
window.dataLayer?.push({
event: 'experiment_view',
experiment_name: 'hero_test',
experiment_variant: variant
})
```
---
## Architecture
```
┌─────────────────────────────────────────────────────────────────────┐
│ A/B TESTING FLOW │
├─────────────────────────────────────────────────────────────────────┤
│ │
│ 1. ASSIGN (Edge Middleware) │
│ ══════════════════════════ │
│ Request → Check cookie → Random assign → Set cookie → Response │
│ ✓ No flicker (server-side) ✓ Consistent (cookie-based) │
│ │
│ 2. RENDER │
│ ═════════ │
│ Server/Client Component → Read cookie → Show variant │
│ │
… Author text anchors workflow facts; Fluxly only indexes current sections, terms, files, and commands.
sections -> Quick Start → Architecture → Workflow → Statistical Methods (Choose One) → Key Patterns → Multiple Concurrent Experiments
terms -> Stack · Why DIY? · Frequentist · Bayesian · Multi-Armed Bandit · Contextual Bandit · Quick Bayesian (Beta-Binomial) · Full analysis guide
files/cmd -> experimentvariant · exp${name} · A/B · Next.js · GA4/GTM · middleware.ts · next/server · Server/Client
body sha256 -> 7512d8f6e928
Decide Fit First
Design Intent
How To Use It
Boundaries And Review