What it is. Tasks in Checked Off can carry an optional energy level requirement - what kind of state you need to be in to actually do the thing. In the daily view, you set your current energy level, and the list sorts to surface tasks matched to how you are right now. Both the daily-view energy rating and the energy column in task views are optional and removable - overhead you can turn off if it doesn’t help you.
The problem it solves. GTD introduced context as a filter - where are you, what tools do you have, can you actually do this task from here. Context is still useful, but it’s not the whole picture. Context answers whether a task is physically possible right now. It does not answer whether you are in a state that can do it.
For many people - and almost universally for people with ADHD or variable-energy conditions - the gap between “this task is available” and “I can start this task” is the entire problem. A list filtered only by context contains plenty of tasks you cannot, in this moment, touch. Staring at them does not help. It mostly produces the feeling of being a person who should be doing a thing they cannot currently do.
The research behind it. ADHD research has documented for decades that available executive function fluctuates throughout the day in a way that healthy dopamine regulation smooths over in neurotypical people (Barkley, 2015). Work on ego depletion and self-regulation, although the literature is contested, consistently finds that self-regulatory demand varies across a day and across individuals. Loehr and Schwartz (Loehr and Schwartz, 2003) argued - outside the clinical literature - that energy management, not time management, is the actual constraint on sustained performance.
Checked Off treats energy as internal state, explicitly distinct from GTD’s external context. A task’s energy requirement is a property of the task. Your current energy is a property of you. When they match, the task becomes possible. The energy lens supports a momentum strategy - start with low-energy work to build initiation flow before attempting high-demand work - that is how a lot of people actually get things done, as opposed to how productivity advice usually says they should.