Open with the problem you are solving, not your preferred technology. What kind of user will use this, how often, and what happens today? A vendor who understands the goal can propose an alternative that costs less; a team that receives only a list of screens can only price the list as written.

Define what is included as user stories or scenarios: who does what, and what happens next. Just as important, symfony erp state explicitly what is out of scope. A written out-of-scope list prevents more disagreement during acceptance than the rest of the brief combined. Mark too which parts are firm and which may still change — the difference changes the price, and concealing the open questions helps nobody.

Write down the hard constraints. These include the platforms and custom mobile app development services involved, the data you have and where it lives, regulatory obligations, web development company user volumes, target platforms and any technology you are committed to. Where a date is genuinely fixed, say what depends on it: an experienced team can often resequence the work to hit it, provided they hear about it early.

Write down what completion means for each item. Acceptance criteria need not use special syntax: a short paragraph setting out what a user should be able to do will do. That one addition shortens the review at the end by a surprising margin and closes off the most common source of disputes.

One last thing, state what you want in the response. Ask for a breakdown by feature or module, a written list of assumptions, the main risks and a low number and a high number. Treat a wide range as information, not evasion: it normally identifies where your description is thin. From there tighten that section and request a revised number — the revised figure will be much more reliable.