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johann losbar

@johannlosbar

Freelance AI backend engineer and fractional CTO. I ship production LLM agents, RAG pipelines and the API architecture underneath.

France

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What I'm looking for

Senior backend engineer, 15 years: TypeScript / NestJS, Python for AI. I get LLM features into production — agents, RAG, MCP, structured outputs, guardrails, observability — plus the API and data architecture underneath.

Previously EM at Vestiaire Collective, then CTO of a SaaS e-learning platform, where I built a team of ten.

Remote, short or long term. Paris/Berlin (CET).

I'm a freelance AI backend engineer and fractional CTO operating under CodiumLab. I help teams take AI features from prototype to production: agent orchestration, retrieval pipelines, evaluation, and the API and data architecture underneath them - typically in Go, Python (FastAPI) and TypeScript (NestJS) on AWS.

Fifteen years of engineering and ten years of engineering management sit behind that. As CTO at Autrice I built a SaaS platform for creating, localizing and customizing digital learning experiences with AI-assisted content generation, and grew the engineering team to around ten. At Vestiaire Collective I managed a cross-functional team across iOS, Android, backend, frontend and QA, drove the technical roadmap on high-traffic products, and worked on microservices performance and A/B testing. At aufeminin Groupe I recruited, trained and managed seven developers, ran releases and quality processes, and led the migration from legacy code and on-premise infrastructure to PHP 7 and AWS.

That mix is what I bring to clients: I can write the code, and I can also tell you which system not to build.

Experience

Work history, roles, and key accomplishments

Current

Founder & Principal AI Engineer

Current

CodiumLab

Feb 2026 - Present (9 months)

Backend & AI engineering studio. Production AI workflows, API-first systems, fractional CTO.
Clients: Autrice (e-learning SaaS) - NestJS/LangGraph backend: multi-doc RAG, vision indexing, multi-voice TTS, 24-language pipeline (Qdrant, Mistral/OpenAI/Anthropic); Megatec - Next.js + Strapi.
Products: Mestri (Go gateway, NestJS, FastAPI, multi-tenant Qdrant), codiumlab-ai (Python RAG/agents/MCP).

NestJS Python fastAPI Go Next.js RAG LangGraph

Chief Technology Officer

Autrice

Mar 2024 - Dec 2025 (1 year 9 months)

SaaS platform for authoring and delivering e-learning content.
- Defined and drove the platform's overall technical strategy
- Designed the backend architecture and core application services
- Shipped production features built on AI workflows
- Built and managed the engineering team (~10)
- Owned cloud infrastructure, security, CI/CD and operations

Engineering Manager

Vestiaire Collective

Apr 2022 - Mar 2024 (1 year 11 months)

International luxury resale marketplace.
- Managed and structured cross-functional engineering teams (~10), with a strong focus on mentoring and career growth
- Drove the technical roadmap on high-traffic products
- Worked closely with product, data, design and QA
- Improved reliability, performance and delivery standards
- Key partner to product teams on prioritisation, scoping and execution

Agile Development Agile Project Management

Team Lead aufeminin & Marmiton

aufeminin Groupe

Jun 2017 - Apr 2022 (4 years 10 months)

High-traffic digital media platforms (aufeminin, Marmiton) serving millions of users.
- Recruited, trained and managed a team of 7 developers
- Bridge between technical, design and product teams across countries
- Owned releases, quality and delivery processes
- Led the migration from legacy code and on-premise infrastructure to PHP 7 and AWS
- Product Owner / Scrum Master duties

Web developer

aufeminin Groupe

Feb 2016 - Jun 2017 (1 year 4 months)

High-traffic digital media platform (aufeminin).
- Built and shipped new site features
- Ran framework version upgrades
- Built a statistics aggregator for our content on social networks
Zend Framework, PHP 5, Vanilla JS, AngularJS, HTML/CSS3, SASS, jQuery, GitLab, SQL Server, MySQL, BigQuery, Memcache, Fastly

Web developer

ELLIPSA

Nov 2010 - Feb 2016 (5 years 3 months)

Publisher and integrator of geomarketing and mapping solutions.
- Developed and maintained Visiomap, a proprietary mapping platform
- Designed software components combining mapping tools with statistical models (R)
- Automated map generation and client reporting
- Administered servers and databases
Zend, Kohana, PHP 5, JavaScript (ExtJS, OpenLayers), PostgreSQL, MySQL, R