@koryla/netlify

A/B testing for Netlify sites with zero flicker. Runs on Netlify Edge Functions (Deno).

Installation

npm install @koryla/netlify

Setup

1. Add environment variables

In your Netlify dashboard → Site settings → Environment variables:

KORYLA_API_KEY   = sk_live_...
KORYLA_API_URL   = https://koryla.com

2. Create the edge function

// netlify/edge-functions/koryla.ts
import { korylaMiddleware } from '@koryla/netlify'

export default korylaMiddleware({
  apiKey: Deno.env.get('KORYLA_API_KEY')!,
  apiUrl: Deno.env.get('KORYLA_API_URL')!,
})

export const config = {
  path: ['/', '/pricing', '/landing'],
}

3. Create your variant pages

Your variant pages must be real pages in your site:

src/pages/
  index.astro        ← control  (base_url: https://acme.com/)
  variant-b.astro    ← variant  (target_url: https://acme.com/variant-b)

Works with any Netlify-hosted framework: Astro, SvelteKit, Nuxt, plain HTML.

4. Create an experiment in Koryla

Go to your Koryla dashboard → New experiment:

| Field | Value | |-------|-------| | Base URL | https://acme.com/ | | Variant A — Control | https://acme.com/ · 50% | | Variant B | https://acme.com/variant-b · 50% | | Conversion URL | https://acme.com/thank-you |

Set it to Active and you're done.

How it works

User visits /
     │
     ▼
Netlify Edge Function (runs at Deno edge, before your site renders)
     │
     ├── calls Koryla API once every 60s to get experiment config
     ├── reads koryla_sid cookie
     │     ├── cookie present → use existing variant (sticky)
     │     └── no cookie → assign variant by traffic weight
     │
     ├── rewrites request to /variant-b via context.rewrite()
     └── sets cookie for 30 days
     │
     ▼
Netlify serves /variant-b content
Browser sees original URL (/) — no redirect, no flicker

Why this is better than VWO / Optimizely

| | VWO / Optimizely | @koryla/netlify | |--|--|--| | When variant is decided | In the browser, after JS loads | At the edge, before any HTML | | Flicker | Yes (page hides while swapping) | No | | Extra JS on page | ~80–150 KB | 0 KB | | Blockable by ad blockers | Yes | No | | Works without JS | No | Yes |