I built a 3D startup tycoon in a single HTML file (and open-sourced it)

Founder's Way is a browser-based 3D startup simulator. Players begin in a garage with their own business concept and aim to expand it into a headquarters downtown. The game operates on realistic costs, taxes, and turnover. The entire game is contained within a single HTML file, approximately 1 MB in size, which includes CSS, the simulation, the 3D scene, five languages, and pixel icons. The only external script required is three.js r128 from a Content Delivery Network (CDN).

Three key lessons were learned during the development of this game. First, using one HTML file with no build step simplifies accessibility. Anyone can play the game instantly, and it can run from various platforms like GitHub Pages, itch.io, or a direct file double-click. Every change, once merged, goes live within a minute due to GitHub Pages. However, the downside is that navigating through the large file can be cumbersome. Clear section headers and grep commands are helpful in such cases.

Second, creating a voxel office is made efficient by reducing the number of draw calls, which improves performance on mid-range laptops. Initially, the title screen and a full headquarters with dozens of people resulted in around 1,700 draw calls. By merging static scenery, using vertex colors instead of materials, and merging each character by animated group, the draw calls were reduced to approximately 570, with the same number of triangles (~105k).

Shadows also update every other frame, further optimizing performance without sacrificing visual quality.

Third, the game simulates not just a company but the idea behind it. Each business idea has 12 key assumptions, such as price people are willing to pay, conversion rates, churn, and customer acquisition costs. These assumptions have a prior range based on industry benchmarks, a shrinking range as the player learns more, and a hidden truth drawn with a slight bias against optimism to represent real-world optimism.

The truth is discovered through validation tests like interviews, landing pages, and pilots. The game runs 100 simulated worlds for each assumption, showing how often the player survives under various conditions.

Finally, the game's open-source nature allows players to propose changes, including potentially disruptive ones. The system is protected to prevent malicious contributions: main is only merged after the maintainer's approval and a passing smoke test. A Playwright script simulates 60 in-game days in every difficulty to ensure stability.

GitHub Actions review new pull requests with Claude, a coding partner, which provides a JSON verdict (APPROVE, CHANGES, or CLOSE) and feedback based on a JSON schema. The PR is then saved to files, and Claude posts a comment and labels using a plain shell step. Contributors' names are credited in the game, and popular ideas with the most upvotes are built.

The game encourages feedback on the first 10 minutes and welcomes contributions, such as translations, new industries, or mobile layouts. The development of Founder's Way was assisted by Claude, a coding partner.