I am a staff-track backend engineer with 7+ years of contract experience building and scaling distributed systems across healthcare, e-commerce, hospitality, and SaaS. I take ownership of hard reliability and architecture problems, delivering measurable outcomes, and raising the engineering bar on every team. What sets my track record apart is not just technical depth but architectural judgment — knowing when a pattern like CQRS or an outbox solves the actual problem, when a query needs an index versus a data model redesign, and when the right call is to push back rather than ship. Across six engagements, a consistent pattern has emerged: identify the systemic issue behind the immediate pain, make the right architectural decision, and deliver something the team can rely on long after the contract ends.

Kevin O'Neill

I am a staff-track backend engineer with 7+ years of contract experience building and scaling distributed systems across healthcare, e-commerce, hospitality, and SaaS. I take ownership of hard reliability and architecture problems, delivering measurable outcomes, and raising the engineering bar on every team. What sets my track record apart is not just technical depth but architectural judgment — knowing when a pattern like CQRS or an outbox solves the actual problem, when a query needs an index versus a data model redesign, and when the right call is to push back rather than ship. Across six engagements, a consistent pattern has emerged: identify the systemic issue behind the immediate pain, make the right architectural decision, and deliver something the team can rely on long after the contract ends.

Available to hire

I am a staff-track backend engineer with 7+ years of contract experience building and scaling distributed systems across healthcare, e-commerce, hospitality, and SaaS. I take ownership of hard reliability and architecture problems, delivering measurable outcomes, and raising the engineering bar on every team.

What sets my track record apart is not just technical depth but architectural judgment — knowing when a pattern like CQRS or an outbox solves the actual problem, when a query needs an index versus a data model redesign, and when the right call is to push back rather than ship. Across six engagements, a consistent pattern has emerged: identify the systemic issue behind the immediate pain, make the right architectural decision, and deliver something the team can rely on long after the contract ends.

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Experience Level

Expert
Expert
Expert
Expert
Expert
Expert
Expert

Language

English
Fluent

Work Experience

Staff-Track Backend Engineer at Stedi
November 1, 2024 - Present
Owning the core EDI transaction platform end-to-end: architected the event-driven claims pipeline (837P/I/D, 270/271), established org-wide OpenAPI contract standards, hardened authN/Z for HIPAA/SOC 2 compliance, and led chaos engineering and threat-modeling programs for critical payer flows. Key outcomes included idempotent pipelines with exactly-once semantics, reduced integration incidents by ~70%, sub-10ms p95 reads with CQRS read models, improved reliability with circuit breakers and DLQs, SOC 2 compliance, and streamlined on-call signaling via structured logging and SLO dashboards.
Senior Backend Engineer at Talon.One GmbH
April 1, 2022 - October 1, 2024
Led performance and reliability work on the real-time promotion engine: re-engineered Go hot paths, introduced CQRS + DDD domain modeling, shipped an outbox-based reward deduplication system, and owned the SLO/alerting program to reduce alert fatigue. Outcomes included ~55% p99 reduction under peak load, canary/shadow deployments reducing production incidents by ~65%, and stable multi-tenant promotions across enterprise clients.
Senior Backend Engineer at Mews
January 1, 2021 - March 1, 2022
Drove the .NET monolith-to-services migration across reservations, invoicing, and payments; delivered Azure Service Bus event workflows, zero-downtime deployment infrastructure, and New Relic SLO observability. Achievements include eliminating cross-domain deploy conflicts, zero-downtime releases, and reducing reliability incidents by ~50% through end-to-end tracing and RBAC improvements.
Backend Engineer at Fishbrain AB
October 1, 2019 - December 1, 2020
Built and optimized the content and media backend across Rails 6 and Go services; improved GraphQL/REST performance, migrated aggregation pipelines to Go, introduced read-replica routing, and implemented media CDN/pipeline optimizations to reduce cost and improve latency.
Full Stack Engineer at Toggl OÜ
July 1, 2018 - September 1, 2019
Contributed to the V8→V9 API platform across Go backend services, CDC data pipelines, and React dashboards; participated in GKE migration and Terraform-driven infrastructure, reducing flaky tests and enabling more frequent, stable releases.
Software Engineer Intern at Storyblok
February 1, 2018 - June 1, 2018
Shipped content workflow middleware, improved query performance, and expanded API test coverage; gained hands-on experience with TypeScript services, Postgres migrations, Docker packaging, and CI-integrated testing under mentorship.

Education

B.S. in Computer Science at Dublin City University
January 1, 2014 - January 1, 2018

Qualifications

Add your qualifications or awards here.

Industry Experience

Healthcare, Software & Internet, Professional Services, Retail, Travel & Hospitality, Media & Entertainment