Headlessly

Split test pricing, onboarding, and features. Measure with real Stripe revenue, not pageviews.

Create an experiment, define variants, assign traffic, and measure outcomes against real revenue data. headless.ly connects Experiment entities directly to Stripe billing -- so you test business impact, not vanity metrics.

import { Experiment } from '@headlessly/experiments'

const experiment = await Experiment.create({
  name: 'Pricing Page v2',
  type: 'ABTest',
  hypothesis: 'Higher anchor price increases average revenue per user',
  variants: [
    { name: 'control', value: { price: 29 }, weight: 50 },
    { name: 'high-anchor', value: { price: 49 }, weight: 50 },
  ],
  metric: 'mrr',
})

await Experiment.start({ id: experiment.$id })

Create an Experiment

Every experiment starts as a Draft. Define what you are testing, the variants, and which metric determines the winner:

import { Experiment } from '@headlessly/experiments'

const experiment = await Experiment.create({
  name: 'Onboarding Flow',
  type: 'ABTest',
  hypothesis: 'Guided onboarding reduces time-to-activate by 40%',
  variants: [
    { name: 'control', value: { flow: 'self-serve' }, weight: 50 },
    { name: 'guided', value: { flow: 'wizard' }, weight: 50 },
  ],
  metric: 'activation_rate',
})
// experiment.$id -> 'exp_qR7wNxBt'
// experiment.status -> 'Draft'

The weight on each variant controls traffic allocation. Weights are relative -- 50/50 splits evenly, 80/20 sends 80% to control.

Start the Experiment

The start verb transitions the experiment from Draft to Running and begins assigning traffic:

import { Experiment } from '@headlessly/experiments'

await Experiment.start({ id: 'exp_qR7wNxBt' })

Verb Conjugation

Every verb has a full lifecycle -- execute, BEFORE hook, AFTER hook:

import { Experiment } from '@headlessly/experiments'

// Execute
await Experiment.start({ id: 'exp_qR7wNxBt' })

// BEFORE hook -- validate or block
Experiment.starting(experiment => {
  if (!experiment.variants || experiment.variants.length < 2) {
    throw new Error('Experiment needs at least two variants')
  }
})

// AFTER hook -- react to the event
Experiment.started(experiment => {
  console.log(`${experiment.name} is now running with ${experiment.variants.length} variants`)
})

Measure with Real Revenue

Most experimentation tools measure clicks. headless.ly measures actual Stripe revenue because Experiment and Subscription live in the same graph:

import { Experiment } from '@headlessly/experiments'

const result = await Experiment.analyze({ id: 'exp_qR7wNxBt' })
// {
//   variants: [
//     { name: 'control', conversions: 45, mrr_impact: 1305 },
//     { name: 'high-anchor', conversions: 31, mrr_impact: 1519 },
//   ],
//   winner: 'high-anchor',
//   confidence: 0.94,
// }

The mrr_impact is not estimated -- it is computed from real Stripe subscriptions created during the experiment window.

Conclude the Experiment

When you have statistical significance, conclude the experiment and apply the winner:

import { Experiment } from '@headlessly/experiments'

await Experiment.conclude({ id: 'exp_qR7wNxBt', winner: 'high-anchor' })

Experiment.concluded((experiment) => {
  console.log(`${experiment.name} concluded -- winner: ${experiment.results.winner}`)
})

Concluding transitions the status from Running to Completed and emits a Concluded event. All traffic is routed to the winning variant.

MCP Tools

Search for running experiments:

headless.ly/mcp#search

{ "type": "Experiment", "filter": { "status": "Running" } }

Fetch a specific experiment with its results:

headless.ly/mcp#fetch

{ "type": "Experiment", "id": "exp_qR7wNxBt" }

Start an experiment via the do tool:

headless.ly/mcp#do

await $.Experiment.start({ id: 'exp_qR7wNxBt' })
const result = await $.Experiment.analyze({ id: 'exp_qR7wNxBt' })
return result

Event-Driven Automation

React to experiment lifecycle events across your system:

import { Experiment } from '@headlessly/experiments'
import { Campaign } from '@headlessly/marketing'

Experiment.concluded((experiment, $) => {
  if (experiment.results.winner && experiment.results.confidence > 0.95) {
    $.Campaign.create({
      name: `Rollout: ${experiment.name}`,
      type: 'Automated',
      segment: 'all-users',
    })
  }
})

Experiment Types

Type	Use Case	Example
`ABTest`	Compare two or three variants	Pricing page, CTA color
`Multivariate`	Test multiple variables at once	Form length + button color
`Hypothesis`	Validate a business assumption	"Enterprise ICP converts at 2x"

A/B Tests