Ask two people to draw a map from the same verbal directions and their roads will rarely meet in quite the same places. SaaS projects behave similarly. A founder says, "Users can invite their team," while a developer must decide who may invite, what happens to an expired invitation, and whether a removed member keeps access. A technical specification is the shared map that exposes those forks before they are paved with code.

Start with the problem, not the machinery. Name the intended user, the situation they are in, the difficulty they face, and the useful outcome the product should create. Add enough context to explain why the outcome matters and how success will be observed. You do not need to prescribe a programming language or database. A good developer can propose those choices more intelligently when the destination is clear and the terrain is visible.

Next, write the important user flows as sequences. For each one, describe where the user begins, what they do, what the system shows, and how the journey ends. Include the less glamorous branches: an empty account, invalid input, a failed payment, insufficient permission, or an interrupted upload. These branches are not edge decorations. Together they reveal the actual shape of the product, much as plotting more points reveals the curve hiding between them.

Turn the first release into two explicit sets: what is in scope and what is out. Group the in-scope work by user capability, not by a vague label such as dashboard. Then attach acceptance criteria that a person can demonstrate: given a defined starting condition, an action produces an observable result. Out-of-scope items are equally valuable. They stop a sensible future idea from quietly becoming a present obligation and make estimates comparable when you vet developers.

Describe the information and connections the product depends on. What records exist, who may see or change them, what must be retained, and which external services exchange data? State operating expectations in ordinary language: the number of users anticipated, sensitive data involved, important response times, backup needs, availability expectations, and supported devices. These constraints influence architecture even when the founder does not dictate it.

Mark assumptions, unknowns, and decisions separately. An assumption can be tested; an unknown needs investigation; a decision needs an owner and date. Ask prospective developers to identify risks, offer alternatives, and explain what they would clarify before estimating. Their questions are part of the interview. Someone who spots a missing permission rule or an expensive integration dependency is showing more useful understanding than someone who immediately supplies a precise deadline.

Review the specification together and keep it versioned beside the project. When a decision changes, update the map and record the effect on scope, cost, and timing. The document need not be enormous or final; it needs to be specific enough that both parties can point to the same journey and recognise its completion. The curious result is that a modest shared map often creates more freedom, not less: developers can choose a sound route because nobody is still arguing about which city they meant to reach.