Xpo

AI growth tool for X with account analysis, voice-aware drafting, reply discovery, and a companion browser extension.

Portfolio Case Study · Build-in-public post

The idea

Most AI writing tools can generate posts, but they usually don't understand the person they're writing for.

Xpo is built around learning a creator's account, source material, previous content, and positioning so it can help with strategy, drafting, replies, and engagement without flattening everything into the same generic AI voice.

What it does

• Analyzes an X account and builds an initial creator strategy
• Grounds AI outputs in source material, previous posts, and account positioning
• Supports ideation, drafting, revision, replies, and post analysis
• Finds and ranks good reply opportunities
• Generates context-aware replies through a companion browser extension
• Includes authentication, billing, entitlements, and persistent creator workspaces

How it works

X account + source material
          ↓
   creator profile
          ↓
 strategy + voice context
          ↓
      AI workspace
     ↙            ↘
drafting        replies
                  ↓
         browser extension

Technical highlights

• Built a structured AI runtime for planning, drafting, revision, reply generation, and post analysis
• Grounded outputs in creator-provided facts, stories, playbooks, and previous content
• Designed persistent chat threads, memories, source materials, onboarding runs, and product events
• Built APIs for browser-extension authentication, opportunity ranking, and reply generation
• Added Stripe checkout, billing state, webhooks, and entitlement controls
• Implemented multiple onboarding data-source paths with production-safe fallback behavior
• Used Inngest functions for deferred X scraping, context priming, and historical backfill work

Stack

Next.js 16 · React 19 · TypeScript · Tailwind CSS 4 · PostgreSQL · Prisma · Supabase · Groq · Stripe · Inngest

Companion extension

The browser extension adds Xpo directly to the browsing workflow.

It can inspect visible X posts, evaluate which conversations are worth joining, and request reply drafts using the creator's existing voice and account context.

The extension communicates with the main Xpo application through authenticated APIs for:

• opportunity ranking
• reply options
• reply generation
• extension sessions
• interaction logging

Architecture

The shipped application currently runs as a single Next.js deployment in apps/web.

Browser
   ↓
Next.js UI + API routes
   ↓
Domain logic
├── AI runtime
├── onboarding
├── creator memory
├── billing
├── Inngest jobs
└── extension workflows
   ↓
Prisma
   ↓
PostgreSQL

External services provide authentication, model inference, billing, deferred job execution, and X data access.

For a deeper technical breakdown:

• docs/app-architecture.md
• docs/app-diagrams.md

Project origin

The original Stanley for X prototype came from seeing Stan experiment publicly with hiring engineers through build-in-public challenges.

So I made something instead of sending another application.

That prototype eventually became Xpo.

Repo structure

The active application lives in apps/web.

.
├── README.md
├── apps/
│   └── web/
│       ├── app/              # App Router pages and API routes
│       ├── components/       # Shared UI and providers
│       ├── lib/              # AI, onboarding, billing, auth, Inngest, extension logic
│       ├── prisma/           # Schema and migrations
│       ├── public/
│       ├── scripts/
│       ├── package.json
│       └── .env.example
└── docs/
    ├── app-architecture.md
    ├── app-diagrams.md
    └── product-notes/

Run locally

cd apps/web
pnpm install
cp .env.example .env
pnpm dev

Minimum environment variables:

DATABASE_URL
DATABASE_MIGRATION_URL
SUPABASE_URL
SUPABASE_ANON_KEY
SESSION_SECRET
GROQ_API_KEY

Useful commands:

pnpm build
pnpm dev:inngest
pnpm inngest:dev
pnpm lint
pnpm test:ui
pnpm test:e2e
pnpm test:v2
pnpm test:extension

Implementation notes

• Primary persistence is Prisma on PostgreSQL
• Authentication uses Supabase identity with a custom application session
• The current LLM gateway uses the Groq SDK
• Stripe handles checkout, portal access, webhooks, and entitlement state
• Inngest handles deferred onboarding, context-primer, and historical X backfill jobs through apps/web/app/api/inngest
• ONBOARDING_MODE supports scrape, X API, mock, and automatic fallback paths
• Production mock fallback is guarded explicitly
• Product and operator handoff notes live under docs/product-notes