A prototype is a working or simulated representation of a product used to test concepts, flows, interactions, or feasibility before committing to full development. It ranges in fidelity from paper sketches to clickable mockups to fully functional code, and should be chosen at the lowest fidelity that can answer the question being asked. It is the cheapest tool in the product discovery toolbox, and the one most consistently underused by founders who jump straight to building.
The fidelity ladder runs from low to high: paper sketches (cheapest, fastest, useful for concept testing and flow validation), wireframes (digital low-fidelity layouts, Balsamiq-style or in Figma), clickable mockups (interactive Figma / Sketch prototypes that ...