Open with the problem you are solving, not a feature list. What kind of user will use it day to day, how many times a day, and how is the job done today? An estimator who knows what you are trying to achieve will suggest a simpler way to reach it; someone handed only a feature list prices the list as written.
Define what is included as short scenarios: what the user does and what the system does in response. Equally important, state explicitly what is out of scope. An explicit list of exclusions removes more disagreement later than any other single page. Indicate as well which parts are firm and which are still open — honest teams price those differently, and pretending everything is fixed helps no one.
List the constraints. The list covers systems you must integrate with, the data you have and where it lives, security and compliance rules, expected load, which devices matter difference between flutter and react native any technology you are committed to. If there is a hard date, say why: a team can often resequence the work to protect it, provided they hear about it early.
Define what completion means for the important items. Testable acceptance criteria do not require special syntax: a short paragraph stating what must be true when the feature works will do. That one addition shortens acceptance testing considerably and closes off the usual argument at handover.
One last thing, ask for a specific format. Ask for a task-level breakdown, the assumptions behind each number, mobile development agency the risks the team sees and node vs laravel a range rather than a single figure. Take a broad range as useful information rather than evasion: it tells you where your description is thin. At that point rewrite that part and ask again — the next version will be the one worth planning around.
