Backend Engineer

About Little Engine

Little Engine is building the AI-native back office for solo service providers — personal trainers, stylists, tutors, massage therapists, dog walkers, and more. Our mobile app automates scheduling, payments, and client communication — entirely over SMS — replacing a mess of Venmo, Notepad, and texting with a clean, intelligent assistant that works behind the scenes.

We closed a multi-million dollar pre-seed.

The team includes repeat founders who’ve built and sold award-winning apps — including one of Apple’s Best Apps of the Year.

What you'll work on

React Native app for solo entrepreneurs in the US — a back-office tool that helps them manage scheduling, payments, and client communication from their phone. The app is their daily driver for running the business, so reliability, performance, and polish matter.

The stack

• Language & framework: Python 3.12, FastAPI, Pydantic v2, uv (deps/lockfile)
• Data & persistence: PostgreSQL, SQLAlchemy 2 (async) with asyncpg + psycopg 3, Alembic migrations, Redis
• Async & jobs: Celery (workers + beat) on Redis, uvloop, tenacity for retries/backoff
• AI / LLM: Anthropic Claude, Model Context Protocol (MCP) tool server via FastMCP, relevance-classifier agents
• Backend integrations: Twilio (SMS, Voice, Verify, messaging), Stripe, Firebase (Firestore, Cloud Messaging), Google Calendar/OAuth, Cloudflare R2 (S3-compatible via boto3) + CDN, Amplitude, Sentry
• Tooling: Docker (multi-stage) + Compose, GitHub Actions CI/CD, GCP (Cloud Run, Artifact Registry, Workload Identity Federation, Cloud SQL, Memorystore), Ruff, mypy + ty, pre-commit, pytest (asyncio/xdist/cov) + Dockerized E2E harness

What we're looking for

• Senior-level experience shipping and operating production Python backend services (typically 5+ years, but we care more about depth than tenure)
• AI coding agents are a normal part of the daily workflow — we delegate, review, and steer agent output rather than treating it as a novelty
• Strong Python fundamentals — async/await, typing — and sound REST API design instincts
• You've owned third-party integrations end-to-end, especially payments (Stripe) and calendars (Google Calendar/OAuth) — and you know these domains are where the hard problems hide: webhooks, idempotency, retries, reconciliation, time zones, and recurring events
• Hands-on with FastAPI, SQLAlchemy (async), and Pydantic; comfortable working inside a Clean / Hexagonal architecture and respecting its boundaries
• Fluent with background processing on Celery + Redis — webhook-driven flows, idempotent task design, and getting eventual-consistency right
• Strong with PostgreSQL — schema design, migrations (Alembic), and reasoning about query behavior when the work calls for it
• Experience wiring up other platform SDKs — Twilio, Firebase (Firestore, Cloud Messaging), Cloudflare R2/S3 (or equivalents)
• Comfortable with Docker, GitHub Actions CI/CD, and deploying to the cloud (GCP / Cloud Run or equivalent)
• A real testing discipline — unit, integration, and end-to-end — because money and bookings have to be correct
• Comfortable working across a time-zone gap with a US-based product team

How we work

• The engineering team is based in Poland; the product team is in the US. Expect meaningful overlap with US hours for product conversations, and asynchronous-by-default work the rest of the time.
• Small team, startup pace — scope shifts, priorities move, and shipping matters more than process
• You'll work directly with product and backend, not through a chain of intermediaries — expect to be in scoping conversations, push back on requirements, and shape APIs alongside the people building them
• Engineers own areas of the product end-to-end — you're accountable for a slice of functionality from technical design through production behavior, not just the tickets assigned to you
  

Application note

We use AI tools ourselves, so AI-assisted applications are fine. What we do not want is a generic AI-written summary of this job post.

Please include a short section titled “Boring production detail” and describe one specific issue you have personally dealt with in production: a webhook retry, payment reconciliation problem, OAuth/token edge case, calendar time-zone bug, recurring-event sync issue, slow query, unsafe migration, or background-job duplication.

Keep it concrete: what broke, how you detected it, what you changed, and what you would monitor afterward.