Begin with the problem you are solving, not your preferred technology. Which people will use it day to day, how many times a day, and what does the process look like without it? A vendor who knows what you are trying to achieve will suggest a simpler way to reach it; someone handed only the requirements as given will price exactly what you asked for.
Describe the scope as concrete flows: what the user does and what the system does in response. Equally important, state explicitly what you are not building. An explicit list of exclusions prevents more friction during acceptance than any other single page. Also mark which decisions are settled and which may still change — honest teams price those differently, and pretending everything is fixed helps nobody.
List the constraints. This means existing systems the software development staff augmentation has to talk to, the data you have and where it lives, security and monolith vs microservices compliance rules, traffic expectations, which is better livewire or react supported browsers or devices and any technology you are committed to. If there is a hard date, say why: a team will often cut the right scope to protect it, but only if they know it exists.
Define what done means for each item. Testable acceptance criteria need not use any formal notation: a plain-language note describing what must be true when the feature works is sufficient. This one section reduces acceptance testing by a surprising margin and closes off most late-stage disagreement.
Finally, ask for a specific format. Request a task-level breakdown, the assumptions behind each number, the main risks and a low number and a high number. Treat a wide range as a signal about the brief: it usually points to exactly which requirement is unclear. At that point clarify that area and ask for a new estimate — the next version is far closer to reality.
