Mid-Senior Fullstack Developer (Python/React)

We are building a B2B SaaS platform that automates compliance workflows in the fiscal and accounting domain. The product ingests standardized XML and PDF files (including XML files up to 500+ MB), applies a documented business rules engine with 170+ reconciliation rules, and delivers analytical dashboards, anomaly detection and exports.

This is not a "figure it out as you go" project. You will receive: a consolidated technical specification, field-level parsing reference workbooks (exact XPath mappings, format variants and edge cases already documented from real files), and an interactive HTML design prototype that is the binding visual reference. Domain registered, company incorporated, architecture decided. We are looking for one reliable mid-to-senior developer to build the product from scratch alongside the Product Owner with deep domain expertise



What you will build

Unified file-format detector: identifies document type, period and version from uploaded XML and PDF files and routes to the correct parser (two distinct XML formats per document type, fully documented)
Streaming XML parsers: lxml/iterparse based, memory-stable on files up to 500+ MB; PDF parsing with embedded XML extraction
Asynchronous processing: Celery + Redis with separate heavy/light queues, status polling, full job lifecycle
Business rules engine: 170+ documented reconciliation rules across multiple document types, with configurable thresholds and drill-down to source transactions
Analytical dashboard: tables, charts, trend and anomaly analysis, server-side pagination on 100,000+ row datasets, Excel and PDF export
Multi-tenant architecture: full data isolation per client account, enforced and tested at API level
Subscription billing: Stripe (trial, plans, proration, webhooks, cancellation)


Tech stack (decided)

Backend: Python (FastAPI).

Frontend: React + TypeScript.

Database: PostgreSQL.

Queue: Celery + Redis.

Storage: AWS S3 or Azure Blob.

Auth: Supabase or Auth0 (behind an adapter module, hard requirement).

Payments: Stripe. Hosting: AWS or Azure.

Well-argued alternatives can be discussed at kickoff; the stack will not change mid-project.



How we work (read this before applying)

6 milestones with written Definition of Done and acceptance criteria, agreed upfront
Each milestone delivery includes automated tests written by you: golden-file test suites against pre-validated fixtures, minimum 70% coverage on business logic, static analysis report with zero critical findings
Milestone 2 includes a payment gate: a live proof of concept parsing a 500+ MB XML file via iterparse with a memory profile, before the rest of the milestone proceeds
Weekly written status update (Mondays); demo call at the end of each milestone following a script agreed 3 days in advance
for the duration of the collaboration) before start; full IP transfer
What we are looking for

Proven experience shipping SaaS web applications end to end
Demonstrable experience processing large structured files (tell us the largest XML or CSV you have parsed in production and how)
Familiarity with multi-tenant isolation and async job architectures
Clean code, honest communication, reliable delivery. Domain knowledge is not required, the documentation covers it.


First step

Before any contract, we might assign a small paid technical task (2 to 4 hours): parse a real XML file and return structured data via a REST endpoint. Compensated regardless of outcome.

To apply, answer these two questions in your proposal. Applications without them will not be reviewed.

What is the largest XML or structured file you have processed in production, and what was your approach to memory management?
How would you enforce tenant isolation in a FastAPI + PostgreSQL application, and at which layers?