Why I Built an Outliner

Writing was hard

I once wrote a technical book.

I started writing from the beginning and ended up reworking the structure over and over. Each rewrite would break something elsewhere, so I'd fix that too. Managing the structure of a large document is hard.

While researching how to write better, I discovered outliners. I tried organizing a blog post with one, and the writing went smoothly.

With an outliner, you can write without worrying about phrasing. Get your points down as items first, rearrange the structure later. Formatting comes last, so you can focus on getting ideas out. From then on, I used an outliner whenever I wrote.

Tools keep multiplying

Apart from writing, managing work notes and tasks was also a challenge.

Working independently, I'm often involved in multiple projects at once. Each project uses different tools. When you work with a team, you use the team's tools. Wikis, task trackers, documentation. The more projects, the more tools.

Information ends up scattered across tools, so checking anything means opening a different site or app. It becomes hard to see the full picture.

Trying to consolidate into a personal note app means double-managing alongside the project tools. You lose track of what's current and can't keep up.

After trying many setups, I settled on writing everything in one Markdown file per day. Open 2026-04-10.md, put today's tasks, thoughts, and notes in there. No tool switching, no dependencies — it's just a text file. It wasn't a bad approach.

But as the contents grew, it became hard to see what's where. Finding something from last week's file is tedious. Some editors can collapse sections, but you can't focus on just one part and hide the rest. Text files have no way to manipulate structure.

That's when I tried an outliner for this too. Just create an item for each project and write notes and TODOs underneath. An outliner is as simple as a text file, so it doesn't compete with the project's own tools.

A personal tool used alongside project tools needs to be simple. Outliners fit that requirement.

Looking for the right fit

The outliner I'd been using was great on Mac, but the iPhone experience felt lacking. A web app brought to mobile as-is — the gap from a native app was noticeable.

An outliner that felt equally good on Mac and iPhone, that could handle images alongside text, with data staying on my own devices — I couldn't find one at the time.

Building Kosshi

At the company I joined out of college, I started a service with a colleague. It didn't work out and was shut down, but through that experience, I found that the challenge of building something new was enjoyable in itself. I wanted to try building something on my own, and left at the end of 2021. I was deep into outliners at the time, so what to build was an easy decision.

In 2022, Bike shipped — a native outliner for Mac. I remember thinking they'd beaten me to it. But the direction was slightly different from what I had in mind, so I kept going.

The core design hasn't changed since then. A single outline, a native app, a custom rendering engine, no server. To make a living, I took on freelance work alongside development. The freelance side kept me busy for long stretches, so progress was intermittent. Four years from start to ship. It finally launched in 2026.

A personal thinking tool

I built Kosshi as a personal thinking tool. A place to gather my own notes and thoughts across multiple projects. It's not a replacement for team wikis or task trackers, but a personal tool used alongside them. Collaboration happens in those tools. Kosshi is intentionally kept simple.