Todo Mode: A Permanent Sidebar That Every Other Window Respects

What it does

You nominate one application as the todo app. When the mode is on, that app is pinned to a sidebar on the primary display, and — this is the part that matters — every other movement shortcut treats the display as if it were shrunk by the width of that sidebar.

So a window sent to the right half does not go under the sidebar or overlap it. It goes to the right half of the *remaining* area. The reserved strip stops being something you defend and becomes part of the geometry.

Turning it on

It is hidden by default and has to be unhidden from the terminal before it appears in the menu at all:

defaults write com.knollsoft.Rectangle todo -int 1
killall Rectangle && open -a Rectangle

1. Run the command above and restart the app.
2. Bring the application you want in the sidebar to the front.
3. Open the menu bar menu and choose the item that designates it as the todo app.
4. Enable Todo Mode from the same menu.

What belongs in the sidebar

The obvious answer is a task manager, which is where the name comes from. In practice the feature is more general, and several of these are better uses of it:

• A task list. The intended use. Visible all day without stealing space from anything else.
• A chat client. Contentious — permanently visible chat is a permanently visible interruption. Good for support and on-call work, questionable for deep work.
• A notes scratchpad. Excellent. A capture target that is always in the same place removes the friction that stops people writing things down.
• A terminal running logs. For development, a tail that is always visible without a window to manage.
• A reference document. A spec, a style guide, a brief. This is arguably the strongest use and nothing about it involves todos.
• A music player or timer. Works, but a waste of a whole column on most displays.

The width is not arbitrary: it must be wide enough for the app to be genuinely readable, or you will end up widening it manually, which defeats the purpose. On a 27-inch display a quarter is usually about right; on a laptop, this feature is difficult to justify at all.

Limitations to know before committing

Comparing it to the alternatives

Versus a dedicated Space. A Space gives the app a whole screen and requires a switch to see it. Todo Mode keeps it permanently visible. Different trade-off: switching cost versus screen space.

Versus always-on-top utilities. Floating a window above everything is easier to set up and produces constant overlap, because nothing else knows the window is there. The reservation model is strictly better for anything you want visible all day.

Versus just snapping it to a third. This is the honest comparison, and for many people the answer is that snapping is enough. The difference appears when you use other layouts frequently: without the reservation, every subsequent command overlaps your pinned window and you re-snap it constantly. If you snap your chat window back into place more than twice a day, this feature is aimed at you.

Questions