About

Denis Crespe

A senior enterprise software engineer — and the person behind AI SDD. I've worked on business-critical systems in banking, aviation, insurance and the public sector, in France, Luxembourg and Canada. Today I bring that judgment together with AI to modernize legacy systems safely.

Work with me Try the Klyrio app →
Engineering outcomes I've delivered
7 min → 5 s

Rewrote a buggy Node.js fuel-pricing job in Rust — ~84× faster — deployed in Docker. (GlobalJet / Ausy)

12h → 4h30

Optimized an Oracle PL/SQL batch routine for a major bank. (CACEIS / Crédit Agricole)

Java 17–21

Designed & built Spring Boot / OpenAPI microservices & Vue.js front-ends, 2022–2026. (Atos / UGAP)

Projects

What I've built.

Klyrio — a full product built in Rust with AI SDD
Live product

Klyrio

A full product designed and built end-to-end in Rust with the AI SDD methodology — my live proof that AI-assisted development ships production-grade systems.

Visit Klyrio →
The AI Spec Driven Development methodology homepage
Methodology

AI Spec Driven Development

The home of AI SDD — disciplined, spec-first AI-assisted engineering that keeps architecture, knowledge and quality firmly under human control.

Discover AI SDD →
The chess game built with AI SDD running live in the browser
AI SDD · Episode 1

Let's build a chess game

A hands-on walkthrough applying AI SDD from spec to delivery — building a working chess game step by step under human governance.

Read the episode →
AVA Home — Zigbee sensors and MQTT feeding a central home-automation hub
Open source · IoT

AVA Home

A connected-home platform in Rust: Zigbee sensors over MQTT, event history in PostgreSQL, and heating regulation driving the radiators — observe, store, control.

See it on GitHub →
Timeline of a senior career across banking, aviation, insurance and the public sector
Career

Track record

A senior career of enterprise engineering across banking, aviation, insurance and the public sector — in France, Luxembourg and Canada.

See the timeline →
Contact

Send me a message

Or book a discovery call →
Track record

A senior career across regulated, high-stakes domains.

The systems I work on can't afford to break. That's exactly why discipline — not hype — is at the core of how I use AI.

Ongoing · Klyrio — klyrio.net

Founder & Lead Engineer — Klyrio (built entirely in Rust)

A full product designed and built end-to-end in Rust, using the AI SDD methodology from spec to delivery — my live proof that AI-assisted development ships production-grade systems under strict human governance. See the project → · Try the live app →

RustAI SDDFull product
2022 – 2026 · Atos, Montpellier

Software Engineer — Public sector (UGAP.fr)

Built the cleaning-supplies offer for UGAP.fr: Vue.js front-end and Java Spring Boot back-end. Designed RESTful microservices from OpenAPI 3.0 specs.

Java 17–21Spring BootVue.jsRancher
2017 – 2022 · Ausy, Luxembourg & France

Senior Java Developer / Project & Tech Lead — Aviation (GlobalJet)

Normalized a legacy central database; rewrote a failing Node.js pricing job in Rust (7 min → 5 s); built an ESB for XML message exchange; led a 5-person team on a reliable, scalable microservice architecture (Eureka, Zuul).

RustJava 11ActiveMQ / JMSSpring CloudDocker
2013 – 2017 · Freelance, Luxembourg

C++ & Senior Java Developer — Banking & Public sector

Debugged the C/C++ license manager of the IBSY banking app; optimized Informix SQL and built Java APIs for the Luxembourg Chamber of Deputies; delivered REST web services at CACEIS (fund administration).

C/C++Java 8Oracle / InformixCI / Jenkins
2004 – 2013 · Checkfree / Fiserv, Luxembourg

Java Developer — Private banking & asset management

Designed an enterprise content-management solution (KBL); built the Accurate NXG reconciliation "model" (45 reports, 23 PL/SQL procedures); cut a CACEIS routine from 12h to 4h30.

Java 6Oracle PL/SQLIBM MQ / WebSphere
2001 – 2004 · ITI Ltd, Victoria, Canada

Java / Oracle Developer — Insurance & govtech

Built modules for a life-insurance platform and led legacy data conversion for the BC Ministry of Forests — reverse-engineering the old database and defining the migration strategy in Oracle Designer.

Java 1.4Oracle 8Web ServicesUML
1995 – 2001 · ABC Arbitrage, Paris

Software Engineer — Finance / capital markets

Designed Oracle databases and Visual C++ trading interfaces; built financial reporting and inter-application communication via DCOM; standardized coding practices across the team.

Visual C++DCOMOracle 7/9
Services

Here's where I help — modernize, recover, enable.

Senior, outcome-based engagements that turn fragile legacy systems into modern Rust or Go services — and turn undocumented code back into living business knowledge. AI does the heavy lifting; I keep it under engineering control.

⇄

Legacy → Rust / Go Migration

Incremental modernization, zero big-bang rewrite

I convert legacy code — C/C++, old Java, PL/SQL-heavy logic, buggy Node.js, aging monoliths — into clean, tested, maintainable services in Rust or Go. Old and new run side by side; production never stops. Every step is backed by integration tests and proof-of-execution reports.

What you get

  • Target architecture & migration roadmap
  • Migrated, idiomatic, tested code
  • Integration tests & proof of execution
  • Performance & reliability gains

Ideal when

  • A rewrite feels too risky
  • Performance or stability is failing
  • The original authors have left
  • You're moving to cloud / microservices
Discuss a migration
🧠

Knowledge Base Reconstruction

Turn undocumented code back into a source of truth

Your business rules and architecture are trapped inside the code, and the documentation no longer matches reality. AI explores the living system; I curate and validate the findings (the Humanizer Phase) into an accurate, continuously-updatable knowledge base — not another stale document set.

What you get

  • Reconstructed domain model
  • Business-rule catalog
  • Dependency & data-flow maps
  • Architecture decision records

Ideal when

  • Key engineers are retiring
  • Docs diverged from the code
  • You face an audit or compliance review
  • You're preparing a migration or M&A
Rebuild my knowledge base
⚙️

AI SDD Enablement & Fractional AI-Engineering Lead

Make your team fast with AI — without the debt

I install the AI SDD method inside your own team: tooling, prompt and spec templates, review gates, and the Humanizer Phase. Your engineers learn to use AI as a force multiplier within clear boundaries — so velocity goes up while architectural drift and technical debt go down.

What you get

  • AI SDD playbook tailored to your stack
  • Spec / prompt / review templates
  • Hands-on coaching & pairing
  • Governance & quality gates

Ideal when

  • AI usage is ad-hoc and risky
  • You want speed without losing control
  • You need a senior to set the standard
  • You want capability to stay in-house
Enable my team

Let's talk about your systems.

Whether it's a risky legacy migration or knowledge you're about to lose, I can help you move faster — safely.

Book a discovery call