Why I Built an Editor for AI Coding

I use Claude Code in the terminal. The AI writes code. I don't need an IDE open anymore. But I still need to inspect the files it creates and changes.

The Problem

My workflow looks like this:

• Claude Code runs in terminal
• I tell it what to build
• It writes the code
• I review diffs in the terminal

No IDE. No VS Code. Just terminal + AI.

But I constantly need to check files:

• AGENTS.md with agent instructions
• CLAUDE.md with project context
• .env with API keys
• mcp.json with tool configs
• Source files, scripts, and logs produced during a run

Opening VS Code for this felt absurd. 3+ seconds to load an IDE just to read a markdown file? Plus 500MB of RAM sitting there?

I don't need a second tool managing my whole project. I need to open one file, understand it, and get back to the agent.

The Solution

I built markjason. A native macOS app for the text and code files around an AI workflow, without the weight of an IDE.

Opens in 0.3 seconds. Uses about 100MB RAM. That's it.

Live Sync Changes Everything

The feature I didn't know I needed: live file sync.

I keep AGENTS.md open in markjason while Claude Code works. When the agent updates the file, I see it instantly. No refresh button. No "file changed on disk" dialog. Just live updates.

It's like watching the AI think.

Open Whatever the Agent Produces

Press ⌘O to open Markdown, JSON, env, text, or source files. Supported code formats get syntax highlighting. Files with uncommon extensions still open when their UTF-8 content is valid, either as plain text or detected JSON.

Files in iCloud and other macOS File Provider locations get more reliable opening and retry behavior too. Your existing storage stays in charge.

Make Dense Files Readable

Use ⌘+ and ⌘− to adjust edit-mode text from 10pt to 24pt. ⌘0 returns to the 14pt default, and the app remembers your choice after relaunching.

Token Counting

When you're writing prompts, you need to know if they're getting too long. Hit ⇧⌘I and markjason shows you the token count. Simple.

Who This Is For

You might like markjason if you:

• Use Claude Code, Codex, or Aider in terminal
• Don't keep an IDE open all day
• Find yourself opening VS Code just to check one file
• Want something faster than TextEdit but simpler than an IDE

Who This Is NOT For

If you already have VS Code or Cursor open all day, you don't need this. Your IDE can handle markdown just fine. markjason is for people who've moved past the IDE.

If you use Vim or Nano in the terminal and love it, stick with that. You don't need markjason. But if you ever hit the point where you're annoyed you can't just click around and edit like you would in a proper editor, give markjason a try.

Try It

Free download. No account. No tracking.

Press ⌘O for any supported text or code file. You can also set markjason as the default app for the extensions you open most.