Open with the problem you are solving, not your preferred technology. Who will use the system, with what frequency, and what happens today? A vendor who understands the goal will suggest a cheaper route to it; one who only sees the requirements as given prices your assumptions along with the work.
Define what is included as user stories or scenarios: what the user does and what the system does in response. Just as important, list what is out of scope. An explicit exclusion list saves more argument at delivery time than almost anything else in the document. Also mark which items are decided and which may still change — the difference changes the price, rest vs graphql comparison and hiding it helps no one.
List the constraints. The list covers existing systems the germany software development agency has to talk to, the data you have and where it lives, security and compliance rules, user volumes, target platforms and infrastructure that is already decided. If there is a hard date, explain what drives it: a team will often resequence the work to hit it, but not if the date is a secret.
Write down what completion means for each item. Clear acceptance criteria do not require special syntax: a plain-language note stating what a user should be able to do will do. This one section reduces acceptance testing dramatically and removes the most common source of disputes.
Finally, state what you want in the response. Request a task-level breakdown, a written list of assumptions, the main risks and a low number and a high number. Take a broad range as a signal about the brief: it normally identifies the part of the brief that needs work. At that point rewrite that part and ask again — the next version is much more reliable.
