PenEcho puts GPT-5.6 responses beside handwritten math
PenEcho is an canvas for getting help from GPT-5.6 while writing equations and drawing diagrams by hand. When writing pauses, it sends the relevant area to the model and places an editable draft of the response beside the work. The model can explain a step, answer a question, continue an idea, or flag a possible mistake.
The canvas is logically 20,000 by 20,000, but it creates 512-by-512 tiles only where ink exists. Each request sends a cropped view with position information instead of the entire canvas. Typical requests use a few thousand and fewer than 1,000 , costing a few cents or less depending on the model and provider.
The main benefit is avoiding the need to retype unfinished equations and explain their layout in a separate chat window.
Key points
- Users can freely place handwritten equations, diagrams, and notes.
- Pausing triggers a request using only the relevant part of the canvas.
- appear beside the work as editable drafts.
- Tiles are created only where ink exists, reducing the work needed for a very large canvas.
- A typical request uses a few thousand and under 1,000 , with a reported cost of a few cents or less.