Discovery exists because most estimates go wrong at the requirements stage, not the coding stage. Interviews with stakeholders and users, a review of existing systems and a clickable prototype surface the decisions that change cost and timeline while they are still cheap to change.
Discovery is often contracted on its own, with a fixed price and fixed duration, which lets the client test the working relationship before committing to a larger build. Its outputs, such as the backlog, designs and statement of work, should belong to the client and be usable with any vendor.
Defines the problem
Goals, users and success measures are agreed before building.
Reduces estimate risk
Unknowns are surfaced while they are cheap to resolve.
Concrete outputs
Prioritised scope, prototypes, technical plan and estimate.
Separately contracted
Usually a small fixed-scope engagement ahead of the main build.
Codazz builds this in production — Product Design.