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Justin Stewart
Verified Expert in Engineering
Software Developer
Austin, TX, United States
Toptal member since June 22, 2026
Bio
Justin is a senior back-end/full-stack engineer. He turns complex products and platform needs into reliable, scalable systems. With 10+ years of experience across SaaS, marketplaces, analytics, and AI products, he brings enterprise-ready judgment, strong product instincts, and a record of partnering with product, operations, and leadership teams on business-critical initiatives.
Portfolio
CARTELERA
Next.js, TypeScript, Supabase, Puppeteer, OpenAI, Stripe, Vercel...
Neural Frames
Python, FastAPI, Next.js, TypeScript, PostgreSQL, SQLAlchemy, Alembic...
Lightricks
Ember.js, React, PostgreSQL, Redis, Sidekiq, AWS IoT, Ruby on Rails (RoR)...
Experience
- PostgreSQL - 12 years
- Ruby on Rails (RoR) - 11 years
- Ember.js - 7 years
- Node.js - 5 years
- TypeScript - 5 years
- Next.js - 4 years
- Python - 3 years
- OpenAI - 2 years
Work Experience
Software, Product, and Design Expert
2025 - 2026
CARTELERA
- Implemented an installable Progressive Web App (PWA) with offline support, deep linking, share targets, app shortcuts, and a custom service worker for a mobile-friendly web experience on iOS and Android.
- Built back-end-supported product workflows for bilingual event discovery using Next.js, Supabase, and structured content pipelines, improving discoverability, data quality, and self-service usability.
- Designed and shipped front-end and full-stack product features for venue-based event discovery and self-service event management, including passwordless authentication and operational workflows for 50+ venues.
- Built automated content ingestion and enrichment workflows using Puppeteer, Cheerio, and OpenAI to normalize event data and improve the quality of user-facing content.
Technologies: Next.js, TypeScript, Supabase, Puppeteer, OpenAI, Stripe, Vercel, Ruby on Rails (RoR), REST APIs, JavaScript, User Interface (UI), Artificial Intelligence (AI), User Experience (UX), Code Review, Technical Consulting, Software Architecture, Amazon Web Services (AWS), Project Consultancy, Full-stack, Minimum Viable Product (MVP), Onboarding, Full-stack Development, Back-end, AI-assisted Development, Figma to React, MySQL, Web Development, Technical Architecture, Leadership, APIs, Large Language Models (LLMs), Claude Code, Authentication, Product Design, UX Design, UI Design, Security, Web App UX, Web Design, API Integration, SQL, GraphQL, Claude, Data Modeling, Web App Development, GitHub, Unit Testing
Software and Product Consultant
2024 - 2025
Neural Frames
- Built back-end and product systems across FastAPI, PostgreSQL, and AWS, including RESTful APIs, S3 upload flows, and database schemas supporting audio analysis, artwork generation, and customer-facing product experiences.
- Engineered end-to-end Stripe subscription management with pause/resume semantics, webhook reconciliation, and credit-distribution logic for annual plans, reducing billing disputes and preventing revenue leakage.
- Architected time-series analytics schema and cron-based pipelines with distributed task locks, enabling usage insights for product and finance teams while reducing Sentry alerts by 80%.
- Led end-to-end migration efforts to reduce infrastructure costs, including GPUs and storage audits through quick evolution of models and hardware technologies.
Technologies: Python, FastAPI, Next.js, TypeScript, PostgreSQL, SQLAlchemy, Alembic, Stripe API, Amazon RDS, Sentry, OAuth 2, REST APIs, JavaScript, Google API, React, User Interface (UI), Artificial Intelligence (AI), User Experience (UX), Code Review, Technical Consulting, Software Architecture, Amazon Web Services (AWS), Project Consultancy, Full-stack, Minimum Viable Product (MVP), Onboarding, IT Audits, Full-stack Development, Back-end, Supabase, AI-assisted Development, Figma to React, MySQL, Technical Leadership, Web Development, Technical Architecture, Firebase Cloud Functions, APIs, Platforms, Large Language Models (LLMs), Authentication, Product Design, UX Design, UI Design, Security, Web App UX, Web Design, API Integration, SQL, ActiveCampaign, ActiveCampaign API, Claude, Data Modeling, Web App Development, GitHub, Unit Testing
Engineering Manager, Brand Collaborations
2022 - 2023
Lightricks
- Led engineering through LTX’s acquisition of Popular Pays, managing technical due diligence, team transition, and platform integration while maintaining 99.9% operational uptime.
- Coordinated cross-functional integration plans with product, sales, and executive stakeholders to align technical roadmaps and ensure continuity of a key revenue stream.
- Managed engineering delivery for subscription lifecycle enhancements, RBAC improvements, and monitoring upgrades across a 5-microservice architecture supporting 200,000+ active creators and 500+ brand campaigns.
Technologies: Ember.js, React, PostgreSQL, Redis, Sidekiq, AWS IoT, Ruby on Rails (RoR), Node.js, Ruby, Google Cloud Platform (GCP), User Interface (UI), User Experience (UX), Code Review, I am buying a company and want an expert to review the code to make sure that it does what the seller says it does and as a second step to make it more efficient so that I can copywrite it, Technical Consulting, Amazon Web Services (AWS), Full-stack, Full-stack Development, Back-end, Marketplace Platforms, Marketplaces, MySQL, Technical Leadership, Web Development, Technical Architecture, Leadership, APIs, Platforms, Authentication, Security, Web App UX, Web Design, GraphQL, CRM, Data Modeling, Web App Development, GitHub, Unit Testing
Interim Director of Engineering
2021 - 2022
Popular Pays
- Led engineering efforts during the due diligence period for LTX’s acquisition of Popular Pays, coordinating technical discovery, infrastructure assessments, and codebase audits with the acquiring company’s engineering leadership.
- Led rollout of TikTok integration work from web scraping through early API implementation, coordinating scope, delegation, and delivery across back-end and platform workflows.
- Onboarded a team of 9 engineers in Tel Aviv to the product and delegated work across the platform during a high-change transition period.
Technologies: Ember.js, PostgreSQL, Sidekiq, Salesforce API, Ruby on Rails (RoR), Node.js, REST APIs, Ruby, User Interface (UI), Code Review, I am buying a company and want an expert to review the code to make sure that it does what the seller says it does and as a second step to make it more efficient so that I can copywrite it, Amazon Web Services (AWS), Full-stack, Onboarding, IT Audits, Heroku, Full-stack Development, Back-end, Marketplace Platforms, Marketplaces, CTO, Technical Leadership, Web Development, Technical Architecture, Leadership, APIs, Platforms, Security, Web App UX, API Integration, JavaScript, Ruby on Rails 8, CRM, Data Aggregation, Data Modeling, Web App Development, GitHub, Unit Testing
Software Engineering Consultant
2020 - 2021
Popular Pays
- Architected and implemented a Salesforce sync pipeline with real-time order synchronization, background processing, rate-limiting logic, and budget tracking, reducing manual reconciliation overhead by 75% and enabling $2+ million in tracked budgets.
- Led Rails 6 platform upgrade across 3 applications, including asset pipeline fixes, authentication stack refactor, ActiveStorage support, and MIME type normalization, restoring green CI and improving developer velocity.
- Implemented end-to-end agency subscription cancellation flows with Sidekiq workers, Stripe webhooks, external API integration, and policy checks, enabling governed self-service and reducing manual billing operations for 200+ agency accounts.
- Designed platform roles and permission systems with automated backfills, eliminating months of manual updates and improving access consistency across 10,000+ client accounts.
Technologies: Ember.js, PostgreSQL, Redis, Sidekiq, Salesforce, Stripe, TypeScript, Ruby on Rails (RoR), Node.js, OAuth 2, REST APIs, JavaScript, Ruby, User Interface (UI), User Experience (UX), Code Review, Technical Consulting, Software Architecture, Amazon Web Services (AWS), Project Consultancy, Full-stack, Heroku, Full-stack Development, Back-end, Stimulus, Turbo, Marketplace Platforms, Marketplaces, Figma to React, Technical Leadership, Web Development, Technical Architecture, Leadership, APIs, Platforms, Authentication, Product Design, Security, Web App UX, Web Design, API Integration, SQL, ActiveCampaign, Ruby on Rails 8, CRM, Mapbox, Data Aggregation, Google Maps API, Data Modeling, Web App Development, GitHub, Unit Testing
Senior Software Engineer
2018 - 2020
Popular Pays
- Led Pinterest API migration across 5 repositories, implementing new network support, OAuth flows, data normalization, and automated backfills to enable ingestion of organic Pinterest metrics for 20,000+ creator accounts.
- Implemented geospatial creator search using Algolia/places.js and rails-geokit with proximity sorting and optimized ActiveRecord queries, improving discovery relevance by 45%.
- Designed campaign-level audience analytics with interactive Chart.js visualizations, historical backfills, and Instagram audience data integration to support data-driven targeting decisions.
- Built campaign metrics CSV export systems with serialization layers and multi-platform data abstractions, reducing manual analytics requests by 60%.
- Built backend and platform capabilities across integrations, search, analytics, and reporting systems that improved the value and operational usefulness of the platform for brands and creators.
Technologies: Ember.js, PostgreSQL, Redis, Sidekiq, Algolia, Chart.js, Ruby on Rails (RoR), Node.js, OAuth 2, REST APIs, JavaScript, Ruby, User Interface (UI), User Experience (UX), Code Review, Software Architecture, Amazon Web Services (AWS), Full-stack, Heroku, Full-stack Development, Back-end, Turbo, Marketplace Platforms, Marketplaces, Figma to React, Technical Leadership, Web Development, Technical Architecture, Leadership, APIs, Platforms, Authentication, Security, API Integration, SQL, ActiveCampaign, ActiveCampaign API, Ruby on Rails 8, CRM, Mapbox, Data Aggregation, Google Maps API, Data Modeling, Web App Development, GitHub, Unit Testing
Software Engineer
2014 - 2018
Popular Pays
- Upgraded Rails from 5.x to 6.0.4.7 and Ruby from 2.6.6 to 2.6.9 across 3 applications, including authentication refactors, test suite stabilization, and security patches.
- Built admin dashboard features, including organization settings, user management, deactivate endpoints, and shipment-tracking workflows with AfterShip integration to support 200+ admin users.
- Implemented PostgreSQL concurrent indexes and bigint migrations to improve query performance by 65% and scale the data model to 5+ million posts without table locks.
- Designed RESTful API endpoints for campaign shipments, deliverables, and content submissions with state-machine-backed workflows and pagination, enabling programmatic campaign management for 500+ brand integrations.
- Authored extensive RSpec, Capybara, FactoryBot, and Mirage test coverage across multiple repositories, increasing CI reliability and automated test coverage to 85%.
Technologies: Ember.js, PostgreSQL, Redis, Sidekiq, Stripe, Ruby on Rails (RoR), OAuth 2, REST APIs, JavaScript, Ruby, User Interface (UI), User Experience (UX), Code Review, Software Architecture, Full-stack, Minimum Viable Product (MVP), Onboarding, Heroku, Full-stack Development, Back-end, Turbo, Marketplace Platforms, Marketplaces, Web Development, APIs, Platforms, Authentication, Security, API Integration, Ruby on Rails 8, Data Aggregation, Google Maps API, Data Modeling, Web App Development, GitHub, Unit Testing
Project History
Eterna
https://eterna.li/Eterna is a digital legacy and sensitive-message delivery product designed to help people securely prepare notes, videos, recovery instructions, and personal messages for loved ones. I led the product from concept through validation and MVP planning as the sole product engineer, defining user personas, core workflows, privacy requirements, check-in logic, recipient delivery flows, and the public landing experience.
The work required balancing emotional UX, trust, security, and operational reliability for a product where failure would have real human consequences. I also developed the go-to-market validation strategy, including audience segmentation, waitlist positioning, and messaging for groups such as grandparents, families, first responders, and people managing illness.
The work required balancing emotional UX, trust, security, and operational reliability for a product where failure would have real human consequences. I also developed the go-to-market validation strategy, including audience segmentation, waitlist positioning, and messaging for groups such as grandparents, families, first responders, and people managing illness.
Skills
Libraries/APIs
REST APIs, Stripe, React, Node.js, Google Maps API, Puppeteer, SQLAlchemy, Stripe API, Sidekiq, Salesforce API, Chart.js, Google API, ActiveCampaign API
Tools
Turbo, Claude Code, Claude, GitHub, Sentry
Languages
TypeScript, JavaScript, Ruby, Python, SQL, GraphQL
Frameworks
Next.js, Ember.js, Ruby on Rails (RoR), OAuth 2, Alembic, Stimulus
Paradigms
Marketplace Platforms, Unit Testing, UX Design, UI Design
Platforms
Mapbox, Vercel, Amazon Web Services (AWS), Heroku, AWS IoT, Salesforce, Algolia, Docker, Amazon, Google Cloud Platform (GCP)
Storage
PostgreSQL, MySQL, Redis, Google Cloud
Industry Expertise
Web Design
Other
User Interface (UI), Code Review, Technical Consulting, Software Architecture, Project Consultancy, Full-stack, Full-stack Development, Back-end, Marketplaces, Web Development, APIs, Platforms, Authentication, Web App UX, API Integration, Ruby on Rails 8, Data Aggregation, Data Modeling, Web App Development, Supabase, OpenAI, Artificial Intelligence (AI), User Experience (UX), I am buying a company and want an expert to review the code to make sure that it does what the seller says it does and as a second step to make it more efficient so that I can copywrite it, Minimum Viable Product (MVP), Onboarding, IT Audits, AI-assisted Development, Figma to React, CTO, Technical Leadership, Technical Architecture, Leadership, Large Language Models (LLMs), Product Design, Security, ActiveCampaign, CRM, FastAPI, Amazon RDS, Cloudflare, GitHub Actions, Firebase Cloud Functions, eCommerce
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