Breeana Bellflower · Creator, Architect, Pioneer, Thinker Seattle, Washington

Principal Engineer · Systems & AI

Breeana Bellflower.

I build the platforms other engineers stand on: agent systems, developer tooling, and observability.

Now: Principal Engineer at OneRail
Focus: AI systems · Platform engineering · Developer experience
Also: Mentored for UW's Data Science & Machine Learning certificate programs

№ 01

Selected systems

01 OneRail · AI Systems · Platform

AI Agent Platform

A platform that spawns specialist AI agents to take on real engineering work, reachable through webhooks, Slack, and GitHub. Each agent runs in its own sandboxed container, deployed from a Kubernetes manifest, with zero standing permissions: a virtual key grants scoped MCP access to the data its job requires, and the key dies with the job.

Every new agent gets its own scoped key, so it can only ever reach what its job needs. Each one is created on demand for the single job in front of it, and nothing more.

Agents · MCP · Kubernetes · Slack · GitHub

Fig. 01 · Spawned per job, scoped by a virtual key.

02 OneRail · Developer Experience · CI/CD

Feature Preview Environments

Open a pull request on a feature/ branch and a live container of that branch appears online, wired into staging. Open PRs in other repos under the same branch name, and the containers discover each other and interconnect automatically. Merge, and it all tears down on its own.

In a system with dozens of repos, that meant demoing a feature before it ever touched main, let alone production.

Containers · GitOps · Multi-repo · Staging

Fig. 02 · Branch-named containers find each other across repos.

03 OneRail · Observability · OpenTelemetry

Observability Platform

OpenTelemetry APM built around a central collector: every service ships its traces, logs, and metrics to one place, in the same shape, so nothing downstream has to guess who sent what. Tail sampling keeps the traces that matter and drops the noise, so latency, errors, and throughput read the same way across the whole system.

Cheap enough to leave on everywhere, and already the reason behind dozens of bug fixes and performance wins.

OpenTelemetry · Traces · Logs · Metrics · Tail sampling · Collector

Fig. 03 · One collector; keep only the traces that matter.

04 Microsoft · Mobile · Accessibility

Dynamics 365 Field Service Calendar

Brought Outlook-grade calendar UX to Dynamics 365 Field Service on mobile and desktop: three calendar views and booking pages working across browsers, Android, and iOS, with full screen-reader support. Offline mode was the hard part: field technicians lose signal constantly, so the calendar had to keep working alone and reconcile when the connection came back. I also built the CI/CD pipelines behind it and worked from Figma alongside the design org to hold the accessibility bar, all inside a codebase serving enterprise customers at Microsoft scale.

React · Offline-first · Accessibility · CI/CD

Field Service booking calendar on a mobile device — Fig. 04 · Three views, every platform, fully screen-readable.

05 Ace Hardware · Platform · Marketplace

Ace Senior Services

Led the creation of the gig-economy platform that became Ace Home Services: customer, servicer, and admin surfaces, built by three full-stack teams under my lead. A large share of the deliverable work was designed or built by me personally: two of the three surfaces end to end, Stripe payments, Azure auth, accessibility testing, responsive UX. Along the way I introduced Azure Boards and an agile workflow to the company.

Stripe · Azure · Accessibility · Agile

Ace Senior Services web application screens — Fig. 05 · Three surfaces, one marketplace.

№ 02

The record

01

OneRail

Principal Engineer · Now

Force multiplication as a job description: the AI Agent Platform, the observability stack, the AI gateway, and the C# observability library and monorepo tooling new services build on. I work with peers across the org on the architecture decisions that come before major scale, including readying the platform for multi-cloud. I also designed and led a platform-wide UI overhaul: a container-presenter split enforced by linting, paired with an atomic design system, with a large share of it implemented by me.
02

OneRail

Director of Engineering

Defined the department's roles and SDLC and bridged product and engineering. Slashed Azure infrastructure spend and cut database CPU to a fraction of its former load while volume doubled. Helped land Lowe's, PepsiCo, and West Marine. Those wins came from delivering on promises under timelines most teams would have missed.
03

OneRail

Senior Software Engineer · Tech Lead

Built and mentored what was, at the time, the org's highest-performing team. I stayed deep in the code myself, adding 3,800 GitHub contributions along the way.
04

Ace Hardware

Lead Software Engineer

Led three full-stack teams creating Ace Senior Services, set the engineering bar, and negotiated scope directly with the business. Much of what shipped was designed or built by me personally.
05

Microsoft

Software Engineer

Rebuilt the D365 Field Service mobile experience: dynamic calendar views, offline mode, custom CI/CD pipelines, and Figma-driven accessibility work with the design org, all inside an enterprise codebase with an enterprise review culture.
06

University of Washington

Instructional Assistant

Alongside industry work: an instructional assistant for the Data Science and Machine Learning certificate programs I graduated from.

№ 03

Nights & weekends

Nights-and-weekends engineering since 2010. These projects are a small sample of a much longer list.

L·01

System-1 Thinking

AI research · 2026

A proof of concept inspired by Jev: I trained an open-weight language model with LoRA to return yes-or-no judgments, choices, and scores from answer-token probabilities. Independent questions share the same context, without generating explanatory text. Built from public documentation and research, with a repeatable training pipeline.

Read the write-up

L·02

Inside a Transformer

Interactive · 2026

An animated walkthrough I built over a weekend to make transformers easier to follow. Step through embeddings, attention, feed-forward layers, next-token prediction, and the KV cache, with a tiny illustrative model that makes the numbers visible.

Explore the walkthrough →

L·03

Machine Learning

Since 2017

OCR systems, classifiers, and a pile of side experiments, most of it built on my own time, and a good chunk of it ended up running in production. University of Washington certificates in Data Science and Machine Learning made it official.

L·04

Refinement

Civilization simulator

A computer-vs-computer civilization simulation, basically an ant farm to watch with friends. Runs are simulated ahead of time, compressed, and streamed in chunks over websockets; every viewer's frame is synchronized to the clock, so the whole room watches the same moment together. Neo-retro shell, chatroom included.

L·05

Custom Operating System

Low-level

An operating system mirroring Linux's capabilities: terminal commands, process scheduling, memory allocation, a file system, hardware interfacing, plus semaphore locks and user privileges. Debugging at this level is brutal, and no project taught me more about how software actually works.

L·06

Verilog Neural Network

Hardware · Senior design

Hardware neural network diagrams and equations

A neural network implemented in hardware description language: a sigmoid approximation drawn from academic papers for the activation function, and high-precision floating point written from scratch. Simulated neurons matching an equivalent software model. My greatest hours-per-insight challenge to date.

№ 04

In print

All essays on Medium

№ 05

Field notes

Astronomy and photography hobbyist, outside whenever the weather allows. Last year I finished a long-running quest: walking the 1,440 miles Frodo covered from the Shire to Mount Doom, logged one mile at a time, most of them on Pacific Northwest trails and shorelines.

Mount Rainier shrugging off clouds above a treeline and lake

A rock jetty reaching into the Pacific, gulls overhead

Tatoosh Range peaks over evergreen forest

№ 06

About the author

I'm a Principal Engineer, and former Director of Engineering, at OneRail in Seattle. My work lives where systems architecture meets AI: agent platforms, model gateways, observability, and the developer experience that holds it all together.

I've been building my own ML models since 2017, mostly OCR and classifiers, on my own time, and a fair amount of it made its way into production. I earned the University of Washington's Data Science and Machine Learning certificates, and later mentored for both programs.

Before engineering I was a classroom educator, and it stuck: explaining things well is half my job, whether the audience is a new hire, an executive, or a room of students. Away from the keyboard I spend time with my wife and child, introducing our little one to the wonder and complexity of the world. I'm also under a night sky, behind a camera, on a long trail, or in a video game.

Languages: TypeScript · Python · React · C#
Expertise: Systems architecture · AI systems · Database management · Data engineering
Databases: MySQL · Postgres · CosmosDB · Elasticsearch · ClickHouse
Cloud: Azure · Heroku · GCP
Human · teaching most of all, and I have a knack for it: Teaching · Leadership · Mentorship · Clear communication

Study

CSU Sacramento · B.S. Computer Engineering

AI-focused senior design · Tau Beta Pi · Hack State competitive programming

University of Washington · Certificates in Data Science & Machine Learning

Instructional assistant for both programs after graduating

Readings that have influenced me

Signals and Systems · Oppenheim et al.
Operating System Concepts, 9th Edition · Silberschatz, Galvin & Gagne
Logic and Computer Design Fundamentals · Mano et al.
The Zen of Python · Tim Peters

№ 07

Correspondence

Say hello.

You can reach me any time at

breeanabellflower@gmail.com

LinkedIn Medium Instagram

Please don't reach out about sales opportunities. I know it's a challenging job, and I don't want to waste your time!