markjason
your agent made a file. open it.
the fastest way to read specs, edit prompts, inspect code, and manage configs.
built for the only human tasks in agentic coding.
Built for the AI era
Your agents write code. You manage the artifacts.
Open the file your agent made
Markdown, JSON, env, text, and source files.
Even uncommon extensions open when the content is valid UTF-8.
Raw ↔ Read
One key. Toggle between editing and rendered preview.
Scroll position stays put. Sub-line precision.
Outline panel
Every heading in your doc, one click away.
Tracks your position as you scroll. Ctrl+↑↓ to jump.
Live sync with your agents
When something else edits the file, you see it.
No reopening, no refresh, just there.
JSON you can read
Collapsible tree. Types color-coded. Breadcrumb nav.
Validation errors? Click to jump there.
.env made simple
Clean key-value display. Click any value to copy it.
Finally, env files that don't look like a wall of text.
Text at your size
Scale edit-mode text from 10pt to 24pt. ⌘0 resets to 14pt.
Your choice persists when you relaunch.
Share as image
Export any file as a clean, shareable image.
Send specs to non-technical colleagues. No screenshots.
Actually instant
0.3 seconds cold start. 100MB RAM.
Not "fast for an Electron app." Actually fast.
Cloud files that actually open
More reliable opening and retrying for iCloud and other File Provider files.
Your own cloud stays your source of truth.
Why not just use VS Code?
VS Code
- Open app
- Wait for extensions
- Wait for language server
- Read and edit your file
- Wonder why that took 2GB of RAM
markjason
- Double-click file
- Read and edit
- 100MB RAM 🧘
What we'll never add
Get it
Free. No account. No tracking. Just an app.
View on GitHub — install instructions & troubleshooting
Pro tip: Press ⌘O to open a Markdown, JSON, env, text, or source file. To make markjason the default for an extension, use Get Info → Open with → markjason → Change All.