Open with the reason this germany software development agency should exist, not a feature list. Who will use this, how many times a day, symfony vs spring and how is the job done today? A vendor who grasps the purpose can propose an alternative that costs less; someone handed only a list of screens can only price your assumptions along with the work.

Describe the scope as short scenarios: what the user does and what the system does in response. Just as important, state explicitly what the first release deliberately excludes. An explicit list of exclusions prevents more disagreement during acceptance than the rest of the brief combined. Mark too which decisions are settled and which are still under discussion — honest teams price those differently, and concealing the open questions only hurts you.

List the constraints. The list covers the platforms and services involved, the data you already hold and its condition, security and compliance rules, traffic expectations, supported browsers or devices and infrastructure that is already decided. Where a date is genuinely fixed, say why: an experienced team can often cut the right scope to meet it, provided they hear about it early.

Write down what done means feature by feature. Clear acceptance criteria do not need any formal notation: a plain-language note describing what must be true when the feature works is sufficient. That one addition compresses the sign-off process dramatically and eliminates the most common source of disputes.

Finally, say what you expect back. Request an itemised estimate, the assumptions behind each number, whatever the team considers risky and an optimistic and a pessimistic figure. Read a wide range as information, not evasion: it usually points to the part of the brief that needs work. At that point clarify that area and ask again — the next version tends to be the one worth planning around.