Statistical A/B Testing
for Google Ads

Stop guessing which campaign wins. Frequentist and Bayesian testing, budget optimization, MCP apps for AI agents, variance reduction -- the full statistical toolkit for Google Ads and GA4.

Sequential Testing Bayesian A/B Variance Reduction Budget Optimization MCP Apps Causal Attribution
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Free tier, no credit card | Google Ads connected in 60 seconds
15
MCP tools for AI agents
60s
To connect Ads + GA4
<200ms
API response time
40%
Faster decisions with CUPED

The Problem

Ad budgets deserve better than gut instinct.

Most marketing teams make optimization decisions based on incomplete data, arbitrary timelines, and tools that weren't built for statistical rigor.

Peeking inflates false positives

Checking results daily without sequential boundaries means your 5% significance level is actually 20-30%. You're calling winners that aren't winners.

Google's built-in experiments lack rigor

Google Ads Experiments offer basic draft-and-test, but no sequential analysis, no variance reduction, no causal attribution. You're flying blind on methodology.

Spreadsheets don't scale

Manual exports, custom formulas, broken pivot tables. Every time you add a campaign or metric, the overhead compounds. Your team should optimize ads, not maintain spreadsheets.

Capabilities

Real statistics. Not dashboards.

The same methods used in clinical trials and particle physics -- applied to your ad campaigns.

Testing

Sequential A/B Testing

O'Brien-Fleming and Pocock group sequential boundaries. Check your test as often as you want without inflating false positives. Stop early when there's a clear winner -- or stop wasting budget when there's no effect.

Efficiency

Variance Reduction

CUPED and CURE pre-experiment covariates reduce noise in your metrics. Reach statistical significance up to 40% faster with the same traffic. Fewer wasted impressions, faster decisions.

Attribution

Causal Attribution

Difference-in-differences on your campaign data. Measure the actual causal impact of a campaign change -- not just a before-after correlation. Isolate what your change did from market noise.

Forecasting

Metric Forecasting

State-space models on your spend, CPC, CTR, and conversions. See where your metrics are heading with confidence intervals. Plan budgets with data, not hope.

Monitoring

Anomaly Detection

Extreme value theory flags unusual spikes in spend, CPC drops, or conversion rate shifts before they drain your budget. Statistical alerts, not arbitrary thresholds.

Automation

Smart Alerts

Webhook and email notifications when a test reaches significance, an anomaly fires, or a forecast crosses a threshold. Route alerts to Slack, PagerDuty, or any endpoint.

Bayesian

Bayesian A/B & Bandits

Beta-Binomial posterior inference for conversion metrics. Thompson Sampling for multi-armed bandits when you need dynamic allocation. Probability-to-beat and credible intervals included.

Optimization

Budget Optimizer

Multi-channel budget allocation to maximize revenue, conversions, or ROAS. Scenario planning with what-if analysis. See how reallocating spend across channels changes your outcomes.

AI-Native

MCP Apps

15 Model Context Protocol tools for Claude, Cursor, and Windsurf. Query experiments, run forecasts, detect anomalies, optimize budgets -- all from your AI coding assistant or agent.

How It Works

Three steps. Real answers.

From connection to verdict in under five minutes.

1

Connect Google Ads & GA4

OAuth sign-in. Pick your ad accounts and GA4 properties. Campaigns, metrics, and conversion data sync automatically. Takes 60 seconds.

2

Configure your experiment

Select a control campaign and a variant. Pick your metric -- CPA, CTR, ROAS, or custom. We calculate sample size, set sequential boundaries, and apply variance reduction.

3

Get rigorous results

The test runs with continuous monitoring. You get a plain-language verdict with effect size, confidence interval, and a clear stop-or-continue recommendation.

Pricing

Start free. Scale when ready.

No credit card required. Upgrade or downgrade anytime.

Free
$0
forever
  • 3 active experiments
  • 1 Google Ads + 1 GA4 account
  • 30 days history
  • Sequential & Bayesian A/B testing
  • Metric forecasting
  • Sample size calculator
  • MCP Apps (read-only)
Get Started Free
Most Popular Pro
$49
per month
  • Unlimited experiments
  • 5 Google Ads + 5 GA4 accounts
  • 1 year history
  • CUPED/CURE variance reduction
  • Causal attribution (DiD)
  • Budget optimizer & scenario planning
  • Anomaly detection + alerts
  • Thompson Sampling bandits
  • Full MCP Apps access
Start Free Trial
Agency
$199
per month
  • Unlimited experiments
  • 50 Google Ads + 50 GA4 accounts
  • 2 years history
  • Everything in Pro
  • White-label report builder
  • Meta-analysis across tests
  • Team management & audit log
  • Portfolio management
  • REST API + TypeScript SDK
  • AI Decision Assist (BYOK)
  • Priority support
Contact Sales
SOC 2 Readiness
Built on NextStat Engine
Open Methodology
EU Data Residency

FAQ

Common questions.

Sequential A/B testing lets you check results as data arrives without inflating false positive rates. NextStat Ads uses O'Brien-Fleming and Pocock group sequential boundaries, so you can stop a test early when there is a clear winner -- or stop wasting budget when there is no effect.

NextStat Ads connects via OAuth 2.0. You sign in with your Google account, pick an ad account, and your campaigns and metrics sync automatically. The connection takes about 60 seconds. You can disconnect at any time from your dashboard.

You can run A/B tests on any Google Ads metric: conversion rate, cost per acquisition (CPA), click-through rate (CTR), cost per click (CPC), return on ad spend (ROAS), revenue per user, and custom metrics you define.

Google Ads Experiments offers basic draft-and-test functionality with a fixed-horizon test. NextStat Ads adds sequential boundaries (stop early without inflating error rates), CUPED/CURE variance reduction (reach significance faster), difference-in-differences causal attribution, metric forecasting, and anomaly detection. It's the difference between a ruler and a laboratory.

MCP (Model Context Protocol) lets AI assistants like Claude, Cursor, and Windsurf call NextStat tools directly. 15 tools are available: list accounts, query experiments, run forecasts, detect anomalies, optimize budgets, check SRM, run Bayesian tests, and more. Your AI agent gets first-class access to your ad analytics without leaving the chat.

Yes. Connect GA4 alongside Google Ads via OAuth. Your GA4 conversion events, sessions, and custom metrics are available as experiment metrics and in forecasting, anomaly detection, and attribution analysis. Metric mappings let you join Ads and GA4 data.

All data is stored in the EU (Hetzner Cloud, Germany) with TLS 1.3 encryption in transit and AES-256 encryption at rest. NextStat is GDPR-compliant by design. OAuth tokens are encrypted with versioned keys and can be revoked at any time.

Stop running tests by gut feel.

Connect Google Ads. Get your first statistically rigorous verdict in minutes. Free tier, no credit card.

Get Started Free