Open with the problem you are solving, not your preferred technology. What kind of user will use the system, how often, and what does the process look like without it? A vendor custom mobile app development services who understands the goal will suggest a cheaper route to it; one who only sees a list of screens will price your assumptions along with the work.
Describe the scope as user stories or scenarios: who does what, outsource aws development and what happens next. Equally important, write down what the first release deliberately excludes. An explicit exclusion list prevents more argument during acceptance than any other single page. Indicate as well which items are decided and which may still change — estimators price uncertainty, and pretending everything is fixed helps nobody.
Set out your constraints. This means the platforms and devops services company involved, the data you already hold and its condition, security and compliance rules, traffic expectations, target platforms and stacks you cannot change. Where a date is genuinely fixed, say why: a team is usually able to rearrange the plan to hit it, provided they hear about it early.
Define what completion means for each item. Acceptance criteria need not use formal language: a short list describing what must be true when the feature works is sufficient. That one addition reduces the sign-off process considerably and eliminates the most common source of disputes.
To close, say what you expect back. Require a task-level breakdown, a written list of assumptions, whatever the team considers risky and a range rather than a single figure. Treat a wide range as a signal about the brief: it usually points to where your description is thin. From there clarify that area and request a revised number — the revised figure tends to be the one worth planning around.
