Senior Full-Stack Engineer (Next.js + FastAPI) – AI B2B SaaS Platform ($1,500 Fixed Milestones)

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: TYPE OF WORK

Full Time

: SALARY

1500

: HOURS PER WEEK

40

: DATE UPDATED

Sep 16, 2026

JOB OVERVIEW

### CRITICAL NOTICE: SENIOR ENGINEERS ONLY
This is a high-stakes, large-scale enterprise SaaS build. We are looking EXCLUSIVELY for a battle-tested Senior Full-Stack Engineer with a proven track record of architecting and shipping complex, scalable production web applications. If you do not have verified experience building end-to-end platforms from scratch with clean code, robust database architecture, and complex 3rd-party API integrations, please do not apply.

### Project Overview
We are building a cutting-edge, autonomous B2B SaaS platform that monitors buying signals, enriches company and contact data, calculates buyer intent using LLMs (Claude 3.5 Sonnet / Gemini), and dispatches autonomous cold outreach sequences.
We already have a complete, production-grade Technical PRD, database schema (PostgreSQL + pgvector), and full architectural blueprints ready. We require a true builder who can take full technical ownership and turn this architectural specification into a production-ready, highly reliable MVP on schedule.
Core Tech Stack
* **Frontend:** Next.js 14+ (App Router, TypeScript), Tailwind CSS, Shadcn/UI.
* **Backend:** FastAPI (Python 3.11+), asynchronous REST APIs, background workers.
* **Database & Search:** PostgreSQL (Supabase or Neon) with `pgvector` enabled for semantic matching.
* **AI Orchestration:** Anthropic Claude 3.5 Sonnet & Google Gemini APIs (enforcing strict, structured JSON outputs).
* **3rd-Party APIs:** ---------- / People Data Labs (data enrichment), Smartlead / Instantly / Resend (email sending), Stripe (subscriptions & webhooks).
* **DevOps & Integrity:** Docker Compose, strict GitHub branch protection, comprehensive automated documentation.
### Project Timeline & Payment Milestones ($1,500 Total Fixed Price)
Work is structured across a strict 6-week timeline. Payments are released strictly upon verifiable code delivery, code review, and successful merge into our private GitHub repository.
* **Milestone 1: Core Setup, Database & UI Foundation ($300 – Weeks 1 to 1.5)**
* Initialize Next.js 14+ (App Router, TypeScript) dashboard with Tailwind CSS & Shadcn/UI.
* Initialize PostgreSQL database with full schema + `pgvector` extension enabled.
* Implement authentication (Supabase Auth / NextAuth) linked to user accounts.
* *Deliverable:* Clean repository pushed to our private GitHub, responsive UI deployed, and DB migrations verified.
* **Milestone 2: Backend Engine & Apollo Data Ingestion Pipeline ($400 – Weeks 2 to 3)**
* Build FastAPI backend microservice with asynchronous route handlers.
* Integrate ---------- (or PDL) API for discovering, filtering, and enriching B2B leads.
* Store and index lead data in PostgreSQL; display dynamic results on the frontend UI table.
* *Deliverable:* Functional end-to-end flow where searching an ICP pulls live leads and saves them to the DB.
* **Milestone 3: AI Scoring, Auto-Copywriting & Outreach Dispatcher ($450 – Weeks 4 to 5)**
* Connect LLM pipeline (Claude 3.5 Sonnet / Gemini) for intent scoring (0–100) and hyper-personalized cold outreach copy generation.
* Integrate outbound email sending API (Smartlead / Instantly / Resend).
* Build an automated background cron worker executing the self-marketing growth loop on autopilot.
* *Deliverable:* End-to-end test where a scored lead automatically generates personalized copy and queues a live test send.
* **Milestone 4: Stripe Billing, Dockerization & Handover Documentation ($350 – Week 6)**
* Integrate Stripe Billing: tiered subscription plans, customer portal, and secure webhook handlers for dynamic credit balances.
* Implement public API key management layer for third-party developer access.
* Containerize the entire application with a clean `docker-compose.yml` (one-click local spin-up).
* Provide comprehensive `README.md` and `SETUP.md` with step-by-step developer deployment instructions.
* *Deliverable:* Successful Stripe sandbox transaction, full container spin-up, and complete code sign-off.
### Mandatory Candidate Requirements
* **5+ years** of professional Full-Stack engineering experience building production SaaS applications.
* Proven mastery of **Python (FastAPI)** and **Next.js 14+ / TypeScript**.
* Direct experience integrating complex 3rd-party REST APIs ( ---------- , Stripe, LLMs).
* Solid hands-on experience with **PostgreSQL** and task scheduling (Celery, Redis, or BullMQ).
* High standards for clean architecture, modular code, and comprehensive documentation.
* Fluent written English and proactive daily asynchronous communication.
### How to Apply (Screening Instructions)
To verify you read this carefully and possess high attention to detail:
1. Put the exact word **"SIGNAL"** as the very first word in your application title/subject.
2. Share links to your **GitHub profile** and **1–2 live SaaS web applications** or complex APIs you personally architected.
3. In 2–3 sentences: Describe your direct experience with **FastAPI**, ** ---------- API**, and **Stripe Webhooks**.
4. Confirm you can start immediately and deliver within the 6-week milestone schedule.

SKILL REQUIREMENT

Next JS PostgreSQL FastAPI

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Senior Full-Stack Engineer (Next.js + FastAPI) – AI B2B SaaS Platform ($1,500 Fixed Milestones)

Please login or register as jobseeker to apply for this job.

TYPE OF WORK

SALARY

HOURS PER WEEK

DATE UPDATED

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