@focus-reactive/payload-plugin-ab

A/B testing plugin for Payload CMS v3 + Next.js. Create page variants directly inside the Payload admin, assign traffic percentages, and route users at the edge — no extra collections, no manual wiring.

Variants live in the same collection as the original page. The plugin injects the admin UI, hooks, and a variant manifest that Next.js middleware reads to route traffic without a database round-trip.

AI Integration Prompt

Copy and paste this prompt into your AI assistant (Cursor, Claude, etc.) to integrate the plugin into an existing Payload + Next.js project.

I want to add A/B testing to my Payload CMS v3 + Next.js project using @focus-reactive/payload-plugin-ab.

## How it works

Variants are regular documents in the same collection as the original page, distinguished by an
injected `_abVariantOf` relationship field. The plugin auto-injects:
- A Variants panel (sidebar) on original pages — lists variants, traffic % inputs, "+ Add new" button
- A "Variant of" badge (sidebar) on variant pages — links back to the original
- Hooks that maintain a variant manifest (a path-keyed JSON map) in a storage adapter
- A `POST /api/_ab/duplicate` endpoint that clones a page with slug `original--{hash}`

The manifest is read by Next.js middleware at the edge to rewrite requests to the correct variant.

## Installation

pnpm add @focus-reactive/payload-plugin-ab

## Step 1 — Register the plugin in payload.config.ts

import { abTestingPlugin } from '@focus-reactive/payload-plugin-ab'
import { payloadGlobalAdapter } from '@focus-reactive/payload-plugin-ab/adapters/payload-global'

const abAdapter = payloadGlobalAdapter({
  serverURL: process.env.NEXT_PUBLIC_SERVER_URL ?? '',
})

// Inside buildConfig({ plugins: [...] })
abTestingPlugin({
  storage: abAdapter,
  collections: {
    // Key = slug of any collection you want to A/B test
    pages: {
      generatePath: ({ doc, locale }) => {
        const slug = doc.slug as string | undefined
        if (!slug) return null
        return locale ? `/${locale}/${slug}` : `/${slug}`
      },
      // generateVariantData is optional — auto-generates:
      // { bucket: variantSlug, rewritePath: generatePath(variantDoc), passPercentage }
    },
  },
})

## Step 2 — Add Next.js middleware

import { createResolveAbRewrite } from '@focus-reactive/payload-plugin-ab/middleware'
import { payloadGlobalAdapter } from '@focus-reactive/payload-plugin-ab/adapters/payload-global'

const storage = payloadGlobalAdapter({ serverURL: process.env.NEXT_PUBLIC_SERVER_URL ?? '' })

const resolveAbRewrite = createResolveAbRewrite({
  storage,
  getBucket: (v) => v.bucket,
  getRewritePath: (v) => v.rewritePath,
  getPassPercentage: (v) => v.passPercentage,
})

export async function middleware(request) {
  const { pathname } = request.nextUrl
  const result = await resolveAbRewrite(request, pathname, pathname, pathname)
  return result ?? NextResponse.next()
}

export const config = { matcher: ['/((?!_next|api|favicon.ico).*)'] }

## Important notes

- generatePath must return a non-null path for variant slugs (e.g. "about--4ji9") since it
  is also used to compute the variant's rewrite path when generateVariantData is omitted.
- Variant documents are hidden from the collection list view automatically.
- The slug field (and tenantField if configured) is read-only on variant documents.
- Percentage validation: the sum of all variant passPercentage values for one page cannot exceed 100.
  A Payload ValidationError is thrown on save if it would.
- For Vercel deployments, swap payloadGlobalAdapter for vercelEdgeAdapter for sub-millisecond
  manifest reads from Vercel Edge Config.
- If the project uses Payload localization, locale-aware manifest entries are written automatically
  — no extra config needed.

How It Works

Variants live inside the same collection as the original page:

pages collection
├── original   slug: "about"       _abVariantOf: null
├── variant A  slug: "about--4ji9" _abVariantOf: <original id>
└── variant B  slug: "about--x2k1" _abVariantOf: <original id>

On every save or delete, hooks recompute the variant manifest — a plain JSON object keyed by URL path — and write it to the storage adapter. Next.js middleware reads the manifest at the edge to rewrite the request before any rendering happens.

Payload Admin  →  afterChange / afterDelete hooks  →  Storage Adapter
                                                              ↓
                                         { "/about": [variantA, variantB] }
                                                              ↓
                                              Next.js Middleware (edge)
                                                              ↓
                                           Route user to original or variant

Installation

pnpm add @focus-reactive/payload-plugin-ab

For the Vercel Edge adapter, also install:

pnpm add @vercel/edge-config

Peer dependencies: payload ^3.0.0. next ^14 || ^15 and react ^18 || ^19 are optional, required only for middleware and analytics respectively.

Quick Start

Step 1 — Register the plugin

// payload.config.ts
import { buildConfig } from "payload";
import { abTestingPlugin } from "@focus-reactive/payload-plugin-ab";
import { payloadGlobalAdapter } from "@focus-reactive/payload-plugin-ab/adapters/payload-global";

const abAdapter = payloadGlobalAdapter({
  serverURL: process.env.NEXT_PUBLIC_SERVER_URL ?? "",
});

export default buildConfig({
  plugins: [
    abTestingPlugin({
      storage: abAdapter,
      collections: {
        pages: {
          generatePath: ({ doc, locale }) => {
            const slug = doc.slug as string | undefined;
            if (!slug) return null;
            return locale ? `/${locale}/${slug}` : `/${slug}`;
          },
        },
      },
    }),
  ],
});

The plugin injects into every configured collection:

• Variants panel (sidebar on original pages) — lists variants with % inputs, add, delete
• "Variant of" read-only relationship (sidebar on variant pages)
• _abVariantOf and _abPassPercentage fields (hidden from editors)
• admin.baseListFilter to hide variant documents from the list view
• beforeChange / afterChange / afterDelete hooks

Traffic percentages

Each variant owns its own _abPassPercentage, versioned together with the variant document: the draft version holds the value you are editing, the published version holds the value the manifest serves. The original page has no stored copy of it.

Editing percentages in the Variants panel stages them in _abPendingPercentages — a virtual field with no database column, sent with the original's own save:

• Save draft on the original writes the new percentages to each variant's draft. Live traffic keeps using the previously published split.
• Publish on the original applies them to the published variants. Only the percentage is published — a variant's unpublished content stays unpublished, and goes live when you publish that variant itself.
• A variant that has never been published takes no traffic, whatever its percentage says.

Variant percentages must total 99% or less, leaving the original at least 1%.

Step 2 — Wire up middleware

// middleware.ts
import { NextResponse } from "next/server";
import type { NextRequest } from "next/server";
import { createResolveAbRewrite } from "@focus-reactive/payload-plugin-ab/middleware";
import { payloadGlobalAdapter } from "@focus-reactive/payload-plugin-ab/adapters/payload-global";

const storage = payloadGlobalAdapter({
  serverURL: process.env.NEXT_PUBLIC_SERVER_URL ?? "",
});

const resolveAbRewrite = createResolveAbRewrite({
  storage,
  getBucket: (v) => v.bucket,
  getRewritePath: (v) => v.rewritePath,
  getPassPercentage: (v) => v.passPercentage,
});

export async function middleware(request: NextRequest) {
  const { pathname } = request.nextUrl;
  const result = await resolveAbRewrite(request, pathname, pathname, pathname);
  return result ?? NextResponse.next();
}

export const config = {
  matcher: ["/((?!_next|api|favicon.ico).*)"],
};

Configuration Reference

Plugin Options

interface AbTestingPluginConfig<TVariantData extends object> {
  storage: StorageAdapter<TVariantData>;
  collections: Record<string, CollectionABConfig<TVariantData>>;
  enabled?: boolean; // default: true
  debug?: boolean; // show manifest Global in Payload admin. default: false
}

CollectionABConfig

interface CollectionABConfig<TVariantData = DefaultVariantData> {
  /**
   * Slug field name used to generate variant slugs: `{original}--{hash}`.
   * Default: 'slug'
   */
  slugField?: string;

  /**
   * Dot-notation path to the tenant field.
   * Scopes percentage validation per tenant; locks the field read-only on variants.
   */
  tenantField?: string;

  /**
   * Returns the URL path used as the manifest key.
   * Return null to skip this document.
   * Called once per locale when localization is enabled.
   *
   * Must also return a valid path for variant slugs (e.g. 'about--4ji9')
   * since it is used to compute rewritePath when generateVariantData is omitted.
   */
  generatePath: (args: { doc: Record<string, unknown>; locale: string | undefined }) => string | null;

  /**
   * Builds the data stored per variant in the manifest.
   * When omitted, auto-generates: { bucket: variantSlug, rewritePath, passPercentage }
   */
  generateVariantData?: (args: {
    doc: Record<string, unknown>; // parent document
    variantDoc: Record<string, unknown>; // variant document
    locale: string | undefined;
  }) => TVariantData;
}

// Default shape when generateVariantData is omitted:
type DefaultVariantData = {
  bucket: string; // variant's slug, e.g. 'about--4ji9'
  rewritePath: string; // result of generatePath(variantDoc, locale)
  passPercentage: number; // _abPassPercentage field value
};

StorageAdapter

interface StorageAdapter<TVariantData extends object> {
  write(path: string, variants: TVariantData[], payload: Payload): Promise<void>;
  read(path: string): Promise<TVariantData[] | null>; // must be edge-compatible
  clear(path: string, payload: Payload): Promise<void>;
  createGlobal?(debug: boolean): GlobalConfig; // optional, used by payloadGlobalAdapter
}

Implement this interface to use any backend (Redis, Upstash, Vercel KV, etc.).

Storage Adapters

payloadGlobalAdapter

Stores the manifest in a Payload Global as a JSON field. Middleware fetches it via the Payload REST API.

import { payloadGlobalAdapter } from "@focus-reactive/payload-plugin-ab/adapters/payload-global";

const storage = payloadGlobalAdapter({
  serverURL: "https://cms.example.com", // required for middleware reads
  globalSlug: "_abManifest", // default
  apiRoute: "/api", // default
});

The Global is hidden from the admin by default. Set debug: true in plugin options to expose it under the System group.

vercelEdgeAdapter

Stores the manifest in Vercel Edge Config for sub-millisecond reads at the edge.

import { vercelEdgeAdapter } from "@focus-reactive/payload-plugin-ab/adapters/vercel-edge";

const storage = vercelEdgeAdapter({
  configID: process.env.EDGE_CONFIG_ID!,
  configURL: process.env.EDGE_CONFIG!,
  vercelRestAPIAccessToken: process.env.VERCEL_REST_API_ACCESS_TOKEN!,
  teamID: process.env.VERCEL_TEAM_ID, // optional
  manifestKey: "ab-testing", // default
});

Required env vars: EDGE_CONFIG, EDGE_CONFIG_ID, VERCEL_REST_API_ACCESS_TOKEN. Create an Edge Config store in the Vercel dashboard and install @vercel/edge-config.

Middleware

createResolveAbRewrite

import { createResolveAbRewrite } from "@focus-reactive/payload-plugin-ab/middleware";

const resolveAbRewrite = createResolveAbRewrite({
  storage, // same adapter as the plugin
  getBucket: (v) => v.bucket, // extract bucket key
  getRewritePath: (v) => v.rewritePath, // extract internal rewrite URL
  getPassPercentage: (v) => v.passPercentage, // enables weighted routing
});

// In middleware:
const result = await resolveAbRewrite(
  request,
  pathname, // visiblePathname — used as the per-path cookie key
  pathname, // manifestKey — key to look up in the manifest
  pathname, // originalRewritePath — where to send 'original' bucket users
);

The three path arguments let you decouple what the user sees, the manifest key, and the internal rewrite target — useful with locale prefixes:

const internalPath = `/${locale}${pathname}`;

await resolveAbRewrite(request, pathname, internalPath, internalPath);

Routing: When getPassPercentage is provided, each variant receives its percentage of traffic; the remainder goes to the original. The plugin validates on save that the sum never exceeds 100%. When getPassPercentage is omitted, all variants and the original share equal probability.

Sticky sessions: Bucket assignment is stored in a per-path cookie so returning users always see the same variant.

Cookie System

| Cookie | Default name | Lifetime | Purpose | | ---------- | -------------------------- | -------- | --------------------------------------------------- | | Bucket | payload_ab_bucket_{path} | Session | Which bucket this user is in | | Visitor ID | ab_visitor_id | 365 days | Persistent visitor identifier for analytics | | Experiment | exp_{path} | 90 days | Bucket name readable client-side by analytics hooks |

Override names by passing a cookies config to createResolveAbRewrite:

import type { AbCookieConfig } from "@focus-reactive/payload-plugin-ab/middleware";

// Define once, share between middleware and analytics
export const abCookies: AbCookieConfig = {
  visitorIdCookieName: "my_visitor_id",
  getExpCookieName: (key) => `ab_exp_${key}`,
};

Use resolveAbCookieNames(config, experimentId) in Server Components to derive cookie names as plain strings for passing to Client Components:

import { resolveAbCookieNames } from "@focus-reactive/payload-plugin-ab/middleware";

const { variantCookieName, visitorCookieName } = resolveAbCookieNames(abCookies, "/en/about");

Analytics integration

Mount <ExperimentTracker experimentId={manifestKey} /> on each variant-served page. It stamps three GA4 event-scoped custom dimensions on every subsequent event:

• fr_ab_experiment — the experiment id (manifest key, e.g. /en/about)
• fr_ab_variant — the assigned bucket (original or a variant slug)
• fr_ab_visitor_id — the ab_visitor_id cookie value

Register these three dimensions in your GA4 property. The @focus-reactive/payload-plugin-analytics A/B tab reads them to compute exposure, conversion-rate, lift, significance, and SRM. Conversions are the analytics plugin's existing lead_action events on the experiment page — there is no separate AB conversion event.

The plugin auto-creates an ab-experiments collection (hidden unless debug: true) that records each experiment's startedAt on first variant publish.

Using ExperimentTracker

// app/[locale]/[slug]/page.tsx  (Server Component)
import { ExperimentTracker } from "@focus-reactive/payload-plugin-ab/analytics/client";
import { resolveAbCookieNames } from "@focus-reactive/payload-plugin-ab/middleware";

export default async function Page({ params }) {
  const experimentId = `/${params.locale}/${params.slug}`;
  const { variantCookieName, visitorCookieName } = resolveAbCookieNames(undefined, experimentId);

  return (
    <>
      {/* page content */}
      <ExperimentTracker
        experimentId={experimentId}
        variantCookieName={variantCookieName}
        visitorCookieName={visitorCookieName}
      />
    </>
  );
}

ExperimentTracker is a Client Component. Props:

| Prop | Type | Required | Description | | ------------------- | -------- | -------- | ------------------------------------------------------------------------ | | experimentId | string | Yes | Manifest key (URL path, e.g. /en/about) | | variantCookieName | string | No | Override the cookie name for variant bucket (use resolveAbCookieNames) | | visitorCookieName | string | No | Override the cookie name for visitor ID (use resolveAbCookieNames) |

Multi-Tenant Support

abTestingPlugin({
  storage,
  collections: {
    pages: {
      tenantField: 'tenant',  // dot-notation path to the tenant field
      generatePath: ...,
    },
  },
})

When set, percentage-sum validation is scoped per tenant, and the tenant field is locked read-only on variant pages.

Localization Support

No extra config needed. When payload.config.localization is set, the plugin iterates every locale on each save and writes a separate manifest entry per locale. locale is undefined when localization is not configured.

generatePath: ({ doc, locale }) => {
  const slug = doc.slug as string | undefined;
  if (!slug) return null;
  return locale ? `/${locale}/${slug}` : `/${slug}`; // '/en/about', '/fr/about'
};

Exports Reference

| Import path | Exports | | ----------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | @focus-reactive/payload-plugin-ab | abTestingPlugin, AbTestingPluginConfig, CollectionABConfig, StorageAdapter, AbCookieConfig, resolveAbCookieNames, ResolvedAbCookieNames, AB_EXPERIMENTS_SLUG, AB_DIMENSION_PARAMS | | @focus-reactive/payload-plugin-ab/adapters/payload-global | payloadGlobalAdapter | | @focus-reactive/payload-plugin-ab/adapters/vercel-edge | vercelEdgeAdapter | | @focus-reactive/payload-plugin-ab/middleware | createResolveAbRewrite, resolveAbCookieNames, AbCookieConfig, ResolveAbRewriteConfig | | @focus-reactive/payload-plugin-ab/analytics | ExperimentTracker, ExperimentTrackerProps, AbCookieConfig, resolveAbCookieNames, ResolvedAbCookieNames | | @focus-reactive/payload-plugin-ab/analytics/client | ExperimentTracker, ExperimentTrackerProps, AbCookieConfig, resolveAbCookieNames, ResolvedAbCookieNames |