Principal Software Engineer

Location: Ireland, Germany, Romania, Estonia

Department: Engineering

Workplace: remote

Employment Type: contract

Description

pubGENIUS is a React.js and Next.js development agency and ad-tech startup. We build websites and apps for clients across the US and Europe, specializing in decentralized finance (DeFi, crypto, NFT, blockchain), fintech, and healthcare, with occasional work in e-commerce and other verticals.

Beyond client work, we operate our own high-revenue web product with a website, mobile app, and machine learning systems powering our ad-tech optimization engine. Performance is not a preference here, it is a core requirement.

We are looking for a Principal Software Engineer, who will be the technical authority, responsible for all development, architecture decisions, and long-term technical strategy across a website, mobile app, and ML-powered ad-tech optimization systems.

This is a full-time independent contractor engagement. You will work hands-on at a senior level where site speed and server performance are core success metrics. You will work directly with stakeholders to set technical direction, remove bottlenecks, and ship production-grade code.

Engagement Details:

• Type: Full-time independent contractor
• Hours: Full-time commitment expected
• Location: Remote (US, Canada, UK, Ireland or Netherlands)
• Clients: US and Europe
• Rate: Competitive, based on experience

What You'll Own

• End-to-end technical ownership of a high-revenue web platform and mobile app
• Architecture design and long-term technical strategy
• Server-side rendering pipeline using Node.js, Fastify 5, and React 19
• Data layer across MySQL and BigQuery
• GCP infrastructure including Cloud Run, Cloud Build, and Global Load Balancer
• Ad-tech integrations including Google Ad Manager, GTM, GTag, and GPT.js
• Performance optimization at scale, where every millisecond counts
• ML pipeline maintenance and optimization for ad-tech performance

Requirements

Must-Have Qualifications

These are non-negotiable. Please only apply if you have strong, production-proven experience in all of the following:

• Node.js with TypeScript in production
• React in a server-side rendering context
• MySQL including database design, query optimization, and ORM usage
• BigQuery for querying and managing large-scale datasets
• GCP with hands-on experience in Cloud Run, Cloud Build, Cloud SQL, and Load Balancing. GCP certification is a significant bonus.

Nice-to-Have Experience

• Ad-tech industry experience including ad serving, yield optimization, and programmatic advertising
• Affiliate marketing experience, particularly with Anura and Everflow
• Cloudflare including CDN configuration, caching strategies, and Workers
• Fastify, especially Fastify 5 patterns
• Flutter for mobile app contribution
• Golang or Rust for high-performance service work
• Machine learning applied to ad-tech optimization (not LLMs or agents)
• Experience in DeFi, crypto, NFT, blockchain, fintech, or healthcare verticals

Benefits

• Fully remote work
• Flexible hours
• Paid vacation and sick days

Application Process

• We do not review applications via LinkedIn DMs or email. Please apply through the application link.
• We do not work with staffing agencies or third-party recruiters. Direct applicants only.

pubGENIUS is an Equal Opportunity Employer; employment with pubGENIUS is governed on the basis of merit, competence, and qualifications and will not be influenced in any manner by race, age, colour, gender, religion, national origin/ethnicity, veteran status, sexual orientation, marital status, gender identity, mental or physical disability, or any other legally protected status.