John Doan • Software / AI / Data Engineer • Published iOS Developer

On the App Store Live 16 apps

Learn English: Pronunciation

Education · iOS 16+ · Free · No tracking · Offline

Vocabulary and grammar trainer for adult ESL learners — 10 themed lessons (140+ words) with native pronunciation, IPA, and example sentences, plus 20 grammar topics with fill-in-the-blank drills. Four accents (US / UK / AU / IN). Fully offline, no tracking.

Swift SwiftUI AVSpeech iOS 16+ Offline

Download on the App Store

Screenshots Support

Family Medical Refill

Medical · iPhone · iPad · Free · No tracking · Offline · Apple Intelligence

The calm caregiver app for medications and appointments. Track refills, injections, doctor visits, and insurance calls — then draft polite messages with Apple Intelligence running entirely on device. No accounts, no cloud, no tracking.

Swift SwiftUI Apple Intelligence On-device AI iOS 26+ Offline

Download on the App Store

Screenshots Support

Three in a Row Duel

Game Application · iOS 17+ · Free · No ads · No tracking · Offline

The classic 3-in-a-row, done right. Pass-and-play on one device or face the computer at Easy, Medium, or Unbeatable (full minimax search). Named players, persistent leaderboard, and a clean modern design.

Swift SwiftUI SwiftData Minimax AI iOS 17+

Download on the App Store

Screenshots Support

LCD Classic Snake

Game Application · iOS 17+ · Free · No ads · No tracking · Offline

The classic snake game with a retro LCD soul. Swipe to steer on a 20×20 grid; pick from three difficulties (Easy, Medium, Hard) with their own scoring. Persistent per-difficulty leaderboard, green-on-black handheld aesthetic, no ads, no tracking.

Swift SwiftUI SwiftData Retro LCD UI iOS 17+

Download on the App Store

Screenshots Support

Job Trail Applications

Productivity · iPhone · iPad · Mac · Free · No ads · No tracking · Offline

A clean, private way to track every job application in one place — company, role, location, date applied, the posting link, and notes — moving each through Applied, Interviewing, Offer, Rejected, and Withdrawn. Stored on device with SwiftData; no accounts, no ads, no tracking.

Swift SwiftUI SwiftData iOS 17+ Offline

Download on the App Store

Screenshots Support

Soccer 2026: Live Scores

Sports · iOS 17+ · Free · Live scores · Offline schedule · No tracking

Companion for the 2026 international soccer tournament: the full 104-match schedule in your local time, live scores and group standings, the knockout bracket, team pages, and kickoff reminders. Live data served through a custom Cloudflare Worker edge proxy; works offline on a bundled schedule.

Swift SwiftUI Live API Cloudflare Worker iOS 17+

Download on the App Store

Screenshots Support

US Citizenship Questions Prep

Education · iOS 17+ · Free · No tracking · Offline

All 128 official USCIS questions for the 2025 civics test. A practice test that mirrors the real interview (20 questions, 12 to pass, ends early once decided), fill-in-the-blank with forgiving oral-style grading, the 65/20 senior list, and My Officials for the answers that change with elections. Fully offline, no tracking.

Swift SwiftUI USCIS 2025 iOS 17+ Offline

Download on the App Store

Screenshots Support

503020: Budget Coach

Finance · iOS 26+ · Free · No tracking · Offline · Apple Intelligence

Turns your monthly income and spending into a clear 50/30/20 view — Needs, Wants, and Savings — and tells you instantly if you're under or over. Tap "Coach me" for 3–5 specific tips generated on device with Apple Intelligence. Save monthly snapshots to watch your savings rate trend. Fully offline, no accounts, no tracking.

Swift SwiftUI Apple Intelligence On-device AI iOS 26+

Download on the App Store

Screenshots Support

Tabwise: Bills & Invoices

Finance · iPhone · iPad · Mac · Free · No tracking · Offline

A private ledger for the money moving in and out of your life or small business — log bills you pay and invoices you're owed, with payment method (online or check), due dates, statuses, receipts, and reminders. A dashboard shows your net position and charts, flags tax-deductible items, and exports to CSV. No accounts, no tracking; optional Face ID lock, and every record stays on device.

Swift SwiftUI SwiftData Swift Charts Face ID

Download on the App Store

Screenshots Support

Cosmic Cadets

Education · Kids 5–8 · iOS 17+ · Free · No tracking · Offline

A gentle, ad-free space math adventure for ages 5–8 — counting, addition, subtraction, comparing, and first multiplication across a 15-level star map, with difficulty that quietly adapts to each child. Earn stars to unlock rockets and alien companions, keep several kid profiles, and check progress in a math-gated Parent Zone. No ads, no purchases, no accounts, no tracking.

Swift SwiftUI SwiftData AVFoundation iOS 17+

Download on the App Store

Screenshots Support

Streak Rings

Health & Fitness · iPhone · iPad · Mac · Apple Watch · Free · No tracking · Offline

A calm habit tracker for iPhone and Apple Watch — tap a habit and its ring fills with a satisfying haptic. Add habits with an emoji, color, schedule, and daily target; track current and best streaks, a 30-day completion rate, and a 28-day history grid. Built for the few seconds you actually have. No accounts, no ads, no tracking.

Swift SwiftUI SwiftData watchOS Haptics

Download on the App Store

Screenshots Support

Price Trail: Drop Alerts

Shopping · iPhone · iPad · Free · No tracking

Stop refreshing product pages. Paste a product link and Price Trail finds the name, photo, and price automatically, re-checks it in the background, and sends a local alert the moment it drops — or crosses your target price. Compare stores, read the price-history chart, and get an on-device "should you wait?" outlook. Syncs between iPhone and iPad via your private iCloud. No accounts, no ads, no tracking.

Swift SwiftUI SwiftData CloudKit Swift Charts

Download on the App Store

Screenshots Support

Homefolio: Home Inventory

Utilities · iPhone · iPad · Free · No tracking · iCloud sync

Photograph what you own, room by room, before you ever need to prove it. Each item keeps its photos, value, receipt, serial number and warranty date — then exports a claim-ready Personal Property Inventory PDF for an insurance adjuster, with every item and every photo, no page cap and no watermark. Warranty reminders arrive before coverage lapses. Syncs through your own iCloud: no account, no server, no ads.

Swift SwiftData CloudKit PDFKit

Download on the App Store

All Apps Support

Toehold: Sudoku Explained

Games · iPhone · iPad · Free · No tracking · Offline

A sudoku that teaches instead of answering. A live panel inventories every technique available on your board right now — “Hidden single ×2 · X-Wing ×1” — recomputed after each move, without saying where. Tap one to highlight the cells that make it true; placing the digit stays your call. Eleven techniques, difficulty graded by the hardest one a puzzle actually requires, every puzzle verified single-solution and solvable without guessing.

Swift SwiftUI Constraint solver iOS 17+

Download on the App Store

All Apps Support

Clean Sheet PDF

Productivity · iPhone · iPad · Mac · Free · No tracking · Offline

Redaction that actually removes the words. Most PDF apps draw a black box over text that stays in the file; Clean Sheet PDF rebuilds the page with no text layer underneath, then re-reads its own output and refuses to save anything it cannot prove came out clean. Forms and signatures are locked into the page. No networking code at all.

Swift PDFKit Core Graphics Mac Catalyst

Download on the App Store

All Apps Support

Stderr

Developer Tools · Mac · Free · No tracking · Offline

A searchable catalogue of real bugs — short Java and Python programs, the output each one actually produced, and the belief that makes people write it that way. Paste the error you are staring at: search runs over captured output, not lesson titles. Every program was compiled and run on real Java and Python installations before shipping.

Swift SwiftUI OpenJDK CPython

Download on the Mac App Store

All Apps Support

Featured Projects (Start Here)

Full Project Index

John's AI Lab (Gemini Agents)

Google Gemini Agents Angular 22 Vercel

Three live Gemini agents: a tool-calling review analyst with streamed traces, a grounded concierge, and schema-validated playable math missions.

Proof: live demo • streamed tool-call traces • agent loop on GitHub

Live Demo

Job Search Agent

Python Claude API RAG / BM25 AWS

Reads a job posting, retrieves matching evidence from a canonical inventory, and drafts tailored bullets — with a human approval gate and grounding enforced in code.

Proof: 33 unit tests • 5 stages • Terraform on AWS ECS

Project page

Vela Commerce — Blazor WebAssembly catalog grid of maritime outfitter products

Vela Commerce (.NET 10)

.NET 10 C# Blazor WASM PostgreSQL 18

A storefront where nothing on first paint depends on a resource that sleeps — browse, search, filter and sort all run client-side, so the shop works with the backend switched off.

Proof: 175 tests • invariants enforced in PostgreSQL • CI gates — no hosted demo yet

Project page

Job Application Tracker (Java)

Java Maven SQLite JUnit

Console-to-Swing build with SQLite persistence, search/sort, and baseline tests.

Proof: screenshots by stage • DB file • run steps • tests

Project page

AI Lab on GKE

GKE Autopilot Workload Identity Terraform Vertex AI

The same agents on Kubernetes: the pod reaches Vertex AI through Workload Identity — no API key in the image, the manifests, or the Terraform.

Proof: "auth":"adc" from the pod • 13 resources, one apply • destroyed same day

Project page

Keyless Pipeline

GitHub Actions OIDC Workload Identity Federation Terraform Cloud Run

Terraform runs in CI, not on a laptop: a merge deploys to Cloud Run, authenticated by a short-lived OIDC token instead of a service-account key. Plan on every PR.

Proof: live "auth":"adc" • plan on PR, apply on merge • no secret in the workflow

Live endpoint

Customer Metrics Pipeline & API

Python FastAPI ETL OpenAPI

ETL produces curated metrics, then FastAPI serves a scoring endpoint with OpenAPI.

Proof: OpenAPI docs • saved artifacts • run steps

Project page

Support Ticket Analytics

Data DuckDB KPIs Dashboard

Support analytics pipeline with ETL, KPI tracking, lightweight text signals, and dashboards.

Proof: DuckDB mart • KPI outputs • dashboard view

Project page

Workflow Board (React)

React 19 TypeScript @dnd-kit Vite

Trello-style drag-and-drop board with WIP limits, mock multiplayer, and cross-tab sync.

Proof: live demo • normalized store • custom hooks

Live demo

Hangman Encyclopedia (Angular)

Angular 22 Signals TypeScript SCSS

Hangman with a collection meta-game — 434 fact-checked entries across 12 volumes unlock as you solve, in light or dark mode.

Proof: live demo • signals store • curated word banks

Live demo

AI Career Assistant

Grounded RAG demo

Live demonstration of retrieval-augmented generation (RAG) applied to this portfolio. Ask a recruiter-style question — the assistant grounds every answer in the projects, tools, and credentials on this site. Same pattern I use in RAG Mini Chat and the iOS apps' on-device assistance layer.

Prompt

Demo note: deterministic client-side sample using portfolio facts (no external AI API call).

Sample response Ready

Connect:

Backend Services (Java + Python)

Backend services and APIs with validation and documented endpoints (OpenAPI).

Data & Analytics (SQL + DuckDB)

Data marts, ETL pipelines, and dashboards with saved artifacts and reproducible runs.

AI Agents & RAG (Gemini + Grounding)

Live Gemini agents with streamed tool calls, grounding, and schema-validated output — plus retrieval prototypes with run logs and debuggable outputs.

TOOLS & WORKFLOW

Day-to-day tooling across coding, cloud, AI, iOS, and data delivery

Current 2026 toolkit. amber = currently learning / next focus.

Java Python Swift / SwiftUI TypeScript Spring Boot FastAPI Django Angular React SQL Docker Terraform GitHub Actions AWS GCP (Vertex AI) Gemini / Claude APIs

IDEs & Code Editors

Daily coding across general-purpose editing, ecosystem IDEs, and Apple's toolchain.

VS Code IntelliJ IDEA PyCharm Xcode

AI Coding Assistants

Modern AI assistants and agentic coding tools for suggestions, refactors, and paired implementation.

Claude (Sonnet / Opus) Claude Code GitHub Copilot Cursor Aider Codex CLI JetBrains AI

iOS / Swift Ecosystem

Native iOS end-to-end: SwiftUI + modern frameworks, on-device storage and AI, App Store delivery.

Swift SwiftUI Xcode Swift Concurrency SwiftData Core Data Combine AVFoundation App Intents Apple Intelligence Swift Testing TestFlight App Store Connect

Version Control & Collaboration

Source-control workflow for branching, code review, pre-commit hooks, and collaborative delivery.

Git GitHub PR review Conventional Commits pre-commit Dependabot

Databases & Storage

Relational, embedded, and key-value stores for production services and rapid prototyping.

SQLite DuckDB JDBC PostgreSQL Redis MongoDB pgvector

Cloud Platforms

Hosting, serverless, object storage, and managed databases for production workloads.

AWS (Lambda · S3 · RDS · IAM) Cloudflare (Workers · R2 · Pages) GCP (Vertex AI · Cloud Run · BigQuery) Vercel Render

CI/CD & Containers

Containerized development, orchestration, automated delivery pipelines, and infrastructure-as-code.

Docker Docker Compose Kubernetes Helm GitHub Actions Terraform / OpenTofu

Observability & Monitoring

Production telemetry — logs, traces, metrics, and error tracking to keep services debuggable in the wild.

Structured logging Sentry OpenTelemetry Grafana Prometheus

AI / LLM Engineering

Agents, retrieval, grounding, on-device LLMs, and the LLM-app SDK stack — the AI work, not the AI-assisted editor.

Google Gemini (AI Studio · Vertex AI) AI agents (function calling · tool loops) Structured output (responseSchema) Streaming (NDJSON agent traces) Apple Intelligence RAG (Retrieval-Augmented Generation) Embeddings Prompt engineering On-device LLM Anthropic API OpenAI API LangChain / LlamaIndex Hugging Face Ollama Chroma / pgvector MLflow

API Development & Testing

Endpoint design, contract documentation, manual exploration, and automated testing across unit, API, and end-to-end.

OpenAPI / Swagger Postman Bruno (Git-native) pytest JUnit 5 Swift Testing Playwright k6 / Locust

Project Management & Communication

Sprint planning, tracking, async documentation, and team communication around implementation.

Confluence Jira Linear Notion Slack Figma Discord Loom

Languages & Frameworks

Day-to-day languages, backend / data / web libraries, and the modern Python + Java + Swift toolchain.

Python Java Swift C# SQL JavaScript TypeScript React Angular Vite HTML / CSS FastAPI Django Pydantic Pandas scikit-learn JUnit 5 .NET 10 Blazor Spring Boot Ruff + uv dbt Polars