I'm Junhua, the developer of MarginDeck and SnapQuizX.

What I'm working on now

My current product is MarginDeck, a local-first Mac app for understanding revenue, direct costs, shared costs, and estimated contribution profit across software products.

I design and build the product myself. The questions that surface during that work—how to model costs, compare products, document assumptions, and review product results—also shape the notes and tools on this site.

How I like to work

I prefer small, legible systems over complicated ones. A useful product should make its assumptions visible, respect the user's data, and solve a specific problem without turning every interaction into a funnel.

• Build focused products with a clear job to do.
• Keep private working data local when the product allows it.
• Separate measured facts from estimates and assumptions.
• Write down the method so a decision can be revisited later.

Why SwingCodeLab exists

A product page can explain what an app does, but it rarely has room for the experiments, trade-offs, and operating lessons behind it. SwingCodeLab is that wider space.

Here I publish field notes for independent developers, browser-based tools that solve one narrow problem, and release notes about projects I am making. The site is personal by design: Junhua Jin is the author, and SwingCodeLab is the name of the workshop.

Transparency matters

I aim to separate measured facts from estimates, explain assumptions, and update material details when they change. Recommendations are based on real use, not a product's commission rate.

SwingCodeLab may include affiliate links and also covers MarginDeck and SnapQuizX, products I own. Those relationships are disclosed clearly wherever they matter.