Software Engineer & Founder

Building high-performance applications and taking products from concept to launch. Passionate about solving hard technical problems and shipping software that people rely on every day.

Get in touchView experience

William Olsson

Stockholm, Sweden

Experience
5+ years
Stack
.NET · TypeScript
Shipped
3 products
GitHub
@LostVirt

Focus Areas

Full-Stack Development

  • Modern web applications
  • API design & integration
  • Database design & management
  • Code profiling & optimization

Systems & Performance

  • High-throughput backend services
  • Distributed systems architecture
  • Reverse engineering & instrumentation
  • Low-level performance tuning

Product Leadership

  • End-to-end product ownership
  • Licensing & authentication systems
  • Release automation & delivery
  • User feedback-driven roadmaps

Additional Competencies

Performance Engineering

Services handling millions of requests per month, memory and CPU profiling, and optimization of hot paths in both managed and native code

Security & Authentication

OAuth/OIDC integration, custom licensing systems, and secured client-server communication for commercial desktop products

Client & User Experience

Direct engagement with users and third-party developers, feedback integration, and tooling that lets non-developers build without code

DevOps & Observability

Docker containerization, Jenkins CI/CD pipelines, and Prometheus/Grafana monitoring for automated, zero-touch releases

Projects

EternalClient logo

EternalClient· OSRS automation client

A high-performance Old School RuneScape automation client with an extensive script API, unlimited instances, packet and injection interaction modes, a low CPU/memory footprint and remote monitoring.

  • Extensive script API for fast bot development
  • Unlimited concurrent instances per machine
  • Packet and injection interaction modes
  • Cross-platform: Windows, Linux and macOS
  • Remote monitoring & CLI launchable
JavaTypeScriptNext.jsPostgreSQLDocker
HoltWalker logo

HoltWalker· OSRS pathfinding API

A high-performance pathfinding API for Old School RuneScape. Resolves optimal routes across every zone and level, honoring quest, skill and item requirements as it walks.

  • Requirement-aware routing (quests, skills, items)
  • 12,000+ transport links: doors, teleports, fairy rings
  • Full coverage of 327M tiles across Gielinor
  • Bank locator with top-5 ranked results
  • Wilderness avoidance & batch REST queries
GoRedisDockerPrometheusGrafana

Technical Skillset

Languages

C#TypeScriptJavaGoRustC++PythonSQL

Backend & Frameworks

.NETASP.NET CoreBlazorFastEndpointsOAuth / OIDC

Frontend & UI

ReactNext.jsTailwindSass

Databases & Storage

PostgreSQLMySQLRedis

DevOps & Observability

DockerJenkinsGitPrometheusGrafana

Reverse Engineering

Java ASMGhidraCheat Enginex86 Assembly

Work Experience

  1. Doubleflow

    Software Developer · Stockholm

    Sep 2021 – Sep 2026

    Intern Sep–Nov 2021, then full-time

    • Led the rebuild of the company's web platform onto a modern ASP.NET Core stack, driving the migration to FastEndpoints and newer .NET versions
    • Rebuilt the legacy game-building system into a visual scripting tool in Blazor, letting non-developers create interactive games, quizzes and training experiences without writing code
    • Built the client-side system that renders and plays those experiences back to users in real time
    • Built operator tooling for customer onboarding, role-based permissions and usage reporting
    C#ASP.NET CoreBlazorFastEndpointsSQL

  2. EternalClient

    Founder & Software Engineer · Self-employed

    Mar 2023 – Apr 2026

    • Founded and shipped a cross-platform desktop application for Windows, Linux and macOS
    • Built the web platform and marketplace in TypeScript, React and Next.js, where third-party developers listed and sold their work
    • Designed a high-performance pathfinding service serving up to 13 million requests per month
    • Built the licensing and authentication system securing communication between client and server
    • Automated build, testing and release so updates reached users without manual installs
    JavaTypeScriptReactNext.jsGoDocker

  3. LostClient

    Founder · Self-employed

    Dec 2019 – Oct 2023

    • Built and ran an automation platform for a large online game, giving players a scripting API to build their own tools
    • Grew it to over 3 million sessions and roughly 20 million hours of runtime
    • Built the licensing, authentication and usage analytics behind it, shaping the roadmap from community feedback
    JavaMySQLRedis

Beyond Code

When I'm not building software, you'll find me out on a trail, behind a drum kit, or taking something apart to see how it works. Curiosity about what happens under the hood is what got me into engineering, and it still shapes how I approach every problem.

Hiking
Drumming
Side Projects
Reverse Engineering
Learning

At a Glance

Based in
Stockholm, Sweden
Languages
Swedish (native), English (fluent)
Background
Self-taught, five years of professional .NET development
Reach
3M+ sessions and ~20M hours of runtime across shipped products
GitHub
@LostVirt

Let's Connect

Looking for new opportunities in full-stack and backend engineering, technical ownership, or founding roles. Particularly interested in performance-critical systems, developer tooling, and products with real users at scale.

Email Me LinkedIn GitHubDownload Resume
Email
williamolsson2000@gmail.com
Location
Stockholm, Sweden / Remote
GitHub
github.com/LostVirt