John McMillan, Senior Full-Stack Software Engineer

25 years building production software, the last 11 in C# and .NET. Fully remote for 19 years. US-based, Eastern time.

Open to full-time remote roles

Email hire@johnmcm.comLinkedInGitHub

This site shows what a senior engineer can do with AI

I started johnmcm.com in June 2026 and have built it with Claude as my coding partner. It now holds over 100 free tools: viewers for Outlook, Publisher, CorelDRAW and OneNote files, iPhone backups, video repair, PDF tools and more, nearly all running entirely in your browser.

The AI writes much of the code. I decide what to build and how it fits together, review what comes back, test it against real files, and own security and deployment. Most of it is in a stack I don't use day to day (Angular, TypeScript, Python and C++ compiled to WebAssembly), and that is the point: experience carries across, and AI shortens the climb.

How I work with AI

  • Direct it and review it. No paste-and-hope: every change is tested, and every tool is checked with a real file on the live site before I call it done.
  • Turn every miss into a guard. When an AI-written fix broke PDF signing in production by calling a function the library no longer had, I typed that library's interface and added a test, so the same mistake cannot ship again.
  • Security by default. An enforced Content Security Policy, integrity-checked scripts, libraries served from this site rather than a CDN, container images pinned by digest, and files that never leave the visitor's device.
  • A safety net on every deploy. Before anything goes live, an automated pass opens every page in a real browser against the production build, most of them with a real file.

Without the AI: rated Expert on Pluralsight Skill IQ in C#, ASP.NET MVC, Entity Framework Core (94th percentile), MySQL (91st), HTML5 (88th) and Bootstrap, all verified 2019 to 2021, before AI coding assistants existed.

A few of the harder pieces

Publisher and CorelDRAW viewers

Open-source C++ libraries for both formats, compiled to WebAssembly with a pinned, checksummed Docker toolchain, plus a renderer for what they return. The library source and patches are published on this site.

Outlook PST viewer

Reads a mailbox file of several gigabytes in a background worker, a block at a time, so the page never holds the whole file in memory.

iPhone Backup Viewer

Messages, photos, contacts, WhatsApp and notes from an iTunes or Finder backup, encrypted or not. Tested against synthetic backups built by a script, so no real person's data is ever needed.

Video Repair

Rebuilds an MP4 or MOV that will not play, using a healthy clip from the same camera as a reference. The repair engine is C++ compiled to WebAssembly and runs on the visitor's machine.

Experience

Senior / Staff Software Engineer 2016 to 2026

Healthcare continuing-education SaaS

Architected and owned a multi-tenant, multi-domain ASP.NET Core platform that delivers accredited courses to tens of thousands of healthcare professionals from one codebase. Product Owner across several products, built a metadata-driven requirement tracking system covering hundreds of courses, mentored junior developers, and used agentic development daily for proof-of-concept prototypes.

Senior Application Developer 2006 to 2015

Healthcare revenue-cycle software

Lead architect and developer of a point-of-sale and insurance verification platform used by hospitals and clinics nationally. Designed a HIPAA-compliant patient financial clearance system, integrated payment processing and HL7 data exchange, and managed an outsourced team of three to five developers.

Application Developer 2000 to 2006

Moved from technical support into the company's first dedicated development role, and built a timekeeping system used by thousands of employees.

Skills

Core
C#, ASP.NET Core and MVC, .NET 6 and 8, Razor, LINQ, JavaScript, jQuery, Kendo UI
Data
SQL Server and T-SQL, query tuning, PostgreSQL, MySQL, SQLite, Entity Framework Core
Integration
REST and Web API, webhooks, OAuth and JWT, payment processing, HL7, HIPAA
Architecture
Multi-tenant SaaS, service-oriented design, domain-driven design, dependency injection
Front end
HTML5, CSS, Sass, Bootstrap, responsive design
Delivery
Git, CI/CD, Docker, Azure, IIS, unit testing, code review, full SDLC ownership
Recently
Angular, TypeScript, Python and FastAPI, WebAssembly, Caddy and nginx
AI
Claude, GitHub Copilot, Cursor, agentic development workflows

Buy a tool's source

Need one of these tools inside your own product? I'm open to selling the source for most of them. A few are built on GPL code, such as the DWG viewer, and can only be passed on under the same licence; I'll tell you which before we talk price. Get in touch.

Full CV and references on request.