Portfolio

Yusuf Erkan Darıyemez — Senior Software Engineer. Work history, company projects and open source — the long version.

Flagship product

live, in production

yokla

Technical Interview Simulation Platform
Founder & Engineer LIVE

A technical interview simulation you enter by picking seniority × field × specialization — then get scored and benchmarked.

Pick seniority × field × specialization, take a scored MCQ interview, and see where you land against everyone else — with progress tracking, practice mode and an optional AI coaching report. 25,000+ questions were AI-generated and put through a multi-layered, independent verification pipeline; the product itself has no runtime LLM dependency (MCQ + deterministic scoring, $0 runtime cost). I designed and built it end to end: architecture, backend, frontend, data model and deployment.

  • Go 1.25 / Echo v5
  • raw pgx (no ORM)
  • PostgreSQL 18
  • Nuxt 4 SSR / Vue 3
  • Pinia
  • Tailwind v4
  • Voyage AI embeddings
  • Gemini Flash-Lite
  • Claude Haiku
  • Docker Swarm
  • GitHub Actions CI
  • nginx + Cloudflare
  • Prometheus + Grafana
  • AI content generation plus independent verification: parallel generation forks → programmatic scans (language, "longest option" tell, topic alignment) → independent auditor + adjudication. Generation/verification on a cheap model, only adjudication on a strong one → ~4-5× cost cut.
  • "Postgres-first, measure before adding": pgvector and Redis were rejected after measurement (cosine scan runs in seconds in Go, latency is RTT-bound). No needless production risk taken.
  • One dataset, three uses: embeddings built with Voyage AI → dedup + in-interview diversity guard (1.7% unfiltered → 0/300 filtered) + topic auditing.
  • JD → interview: embedding collapsed on job-post matching (.NET → devops); a provider-agnostic design let one adapter swap move it to a Gemini Flash-Lite classifier (~$0.00024/post); taxonomy is read from the DB → a new field means zero code.
  • Optional AI coaching report (Claude Haiku): cached per (user, locale), every real call logs tokens + cost → ~$0.002/report; the feature turns off silently when no key is set.
  • In progress: a verifiable yokla score — a shareable, independently checkable result credential.

yokla.dev ↗

Experience

Senior Backend Developer / Team Lead — ITT Teknoloji A.Ş.

2022 – 2026 · Gebze / Kocaeli

Backend infrastructure for ERP, CRM, CMS, donation management, accounting, reporting and payment modules.

  • Designed and built backend infrastructure with Go, Bun ORM and PostgreSQL
  • Led a 7-person cross-functional team (3 backend, 2 frontend, 1 mobile, 1 analyst); drove mentoring and code review
  • Established team-wide backend standards: layered handler/service architecture, ORM conventions, naming rules, migration practices
  • Improved reporting and heavy-query performance through PostgreSQL schema design, query optimization and data modeling
  • Managed deployment and operations with Docker, Kubernetes, Azure, AWS S3 and CI/CD; built asynchronous, scalable systems with Redis and RabbitMQ

Backend Developer — Hayrat İnsani Yardım Derneği

2020 – 2022

Backend-focused development for enterprise web applications.

  • Developed backend-focused features with Go, C#, .NET and Vue.js across analysis, design, development, testing and release
  • Built relational database designs, data models and reporting solutions
  • Supported DevOps, release and production environment management

Company projects

Built at the companies I worked for — described here, source private.

Aid360

Go · Bun ORM · PostgreSQL

Enterprise platform managing donations, project management, CRM, CMS, accounting, sponsorship and payment processes.

  • Led backend architecture and development of donation, sponsorship, accounting and reporting modules
  • Integrated Craftgate and Stripe payment providers plus third-party accounting systems for end-to-end financial flows
  • Built role-based authorization and multi-language content management with Keycloak
  • Developed an AI-powered OCR pipeline (Google Gemini) extracting data from invoices and documents
  • Built asynchronous background processing with RabbitMQ and a custom task scheduler; Redis cache and S3-compatible storage
  • Developed push, SMS and WhatsApp notification infrastructure and operational reporting dashboards

ITT SAR

Go/Fiber · Bun ORM · PostgreSQL

Multi-tenant platform managing teams, inventory, vehicles, warehouses and field operations for search & rescue organizations.

  • Designed and built the layered handler/service backend architecture
  • Developed advanced inventory management: hierarchical category/variant structures, assignment/transfer flows, QR-code equipment tracking
  • Built organization-based multi-tenancy, JWT authentication and role-based authorization
  • Developed an audit-log system capturing before/after values for all critical operations, plus dashboard reporting

Proje Yönetimi

Go/Fiber · Bun ORM · PostgreSQL

Project lifecycle platform: application, execution and closeout with financial reconciliation and document approval flows.

  • Developed multi-stage file approval/rejection flows for 20+ document and step types
  • Built multi-currency financial closeout, expense allocation and category-based reporting
  • Built a concurrent background-job system synchronizing with the CRM

İdari İşler

Go · Bun ORM · PostgreSQL

Corporate fleet & administrative operations system: 18 modules and 130+ API endpoints covering fleet, real estate, procurement and budgeting.

  • Designed and built the layered (handler/service/domain) backend architecture
  • Developed multi-level approval flows (state machine) varying by amount tier for procurement and vehicle requests
  • Implemented S3-compatible storage (MinIO/AWS), Mailgun email and NetGSM SMS integrations; JWT, soft delete and centralized error handling

Kurban · CRM · Saha Takip · Temsilci Takip · Sertifika · İK · Depo & Lojistik

Go · Bun ORM · PostgreSQL

Other modules and products delivered on the same stack.

Open source

Patterns I kept rebuilding in production, extracted into small, tested Go libraries. Every repo: MIT, CI, no dependency bloat.

Products

Tools

PostgreSQL tooling

Money & correctness

Infrastructure building blocks

Integrations

All repositories on GitHub →

Skills

Languages
Go, C#, JavaScript, SQL
Backend
RESTful APIs, microservices, Fiber / Gin / Echo, .NET Core
Databases
PostgreSQL, MSSQL, MySQL, MongoDB
Data access
Bun, GORM, Dapper
Cache & messaging
Redis, RabbitMQ
DevOps & cloud
Docker, Kubernetes, Azure, AWS S3 / MinIO, CI/CD
Observability
Uptrace, structured logging (Zap), performance monitoring
Leadership
team leadership, mentoring, code review, Agile/Scrum

Education

B.Sc. in Computer Engineering — İstanbul Sabahattin Zaim University · 2019 – 2023

Building a system?

Write me about backend architecture, payment infrastructure or PostgreSQL.

yusuf.erkamyed@gmail.com