Technical Documentation & Communication

User stories are a simple way to write requirements from the user’s point of view. The common format is: “As a [user type], I want [goal] so that [benefit].” This keeps the focus on what users needs and why they need it, not just on building features.

A good user story follows the INVEST rule. It should be:

• Independent: It shouldn’t depend on other stories to deliver value.
• Negotiable: The story can change as the team discusses details and learns more.
• Valuable: It must deliver clear value to the user or customer.
• Estimable: The team should be able to estimate the effort needed. I
• Small: A story should fit within a single iteration or sprint.
• Testable: You should be able to confirm whether it’s done through clear acceptance criteria that describe what should happen. For example, “The system sends a confirmation email after signup.”^[1]

User stories work best when they are small slices of real functionality. Slice work vertically — include all necessary parts (front end, back end, data) so the story can actually work. Avoid horizontal slicing, where only one layer (like just front end or just back end) is done, because that doesn’t create usable functionality.

Acceptance criteria define when a user story is complete. They create a shared understanding between product managers, developers, and QA teams about what success looks like. Without clear criteria, teams waste time debating whether features are "done."^[2] Keep in mind that acceptance criteria usually cover functional requirements (what the user story should achieve). Non-functional requirements, like security, scalability, localization, or production readiness, aren’t always listed in the story. Instead, these are included in a team-wide definition of done (DoD) statement.

Write acceptance criteria as testable statements. Use formats like "Given [context], when [action], then [result]." For example: "Given a user has items in their cart, when they click checkout, then they see a payment form with their cart total."

Include both positive and negative scenarios. Define what should happen in normal use cases and edge cases. Consider error states, empty states, and boundary conditions. This prevents surprises during development and testing.

Technical specifications are owned and written by engineers. It defines the system design, architecture, data flows, and integration points. Product managers provide input to make sure user and business goals stay aligned, but the engineering team leads its creation and approval. They usually start with the problem statement from the product requirements document. Next, they explain what users are trying to accomplish and why current solutions fall short. Then they outline the proposed technical approach, including major components, data structures, dependencies, and API interactions.

Technical specifications also include constraints and trade-offs. Every technical decision involves compromises. It’s helpful to record why one approach was chosen over another. This context helps future engineers maintain and extend the system without losing design intent.

System flow diagrams show how data and users move through your product. They reveal dependencies, identify bottlenecks, and help teams spot problems before writing code. Even simple diagrams clarify complex interactions better than pages of text.

Start with user actions and system responses. Use standard shapes: rectangles for processes, diamonds for decisions, and arrows for flow direction. Keep it simple - anyone should understand your diagram without a legend.

Focus on one flow at a time. Don't try to show everything in one diagram. Create separate flows for user registration, checkout, or data processing. This makes diagrams easier to read and maintain.

Third-party developers use your API to make their own apps or services work with your product. They need your API to access your product’s features, send or receive data, or add functionality to their systems. Good API documentation shows them exactly how to do this, so they don’t need to contact your team for help.

Strong API docs should:

• List endpoints clearly
• Show request and response examples
• Explain errors and how to handle them

Keep the structure the same for every endpoint. For example, for REST APIs include:

• The HTTP method (GET, POST, etc.)
• The URL
• Required parameters
• Example responses (both success and error cases)

Use real examples, not just vague descriptions, so developers know exactly what to send and expect. At the start of the docs, explain authentication and rate limits. Developers need to know how to authenticate requests and how many requests are allowed. Finally, add code snippets in popular languages. This saves time and helps developers get started faster.

Data models describe how an application stores and connects information. They help teams understand the data structure, plan new features, and troubleshoot issues efficiently. Clear data model documentation can prevent costly database redesigns in the future. A good data model should document all entities and their relationships, show what data each table holds, and explain how tables connect. It should also include details such as field types, constraints, and indexes, as well as the reasoning behind certain design decisions.

For example, in an e-commerce application, there might be a Users table storing user ID, name, email, and password hash; an Orders table linked to Users by user ID, storing order date and total amount; a Products table with product ID, name, price, and stock; and an Order_Items table linking Orders and Products with quantity details. Relationships include a user placing many orders and each order containing many products, with each product potentially appearing in multiple orders. Proper documentation of this model helps developers build queries, add features like order history, and fix issues such as missing stock. If the Products table later adds a discount field but the documentation is not updated, developers may make errors or confusion may arise.

Modern documentation tools make writing and maintaining docs easier. From wikis to specialized platforms, choose tools (after discussion with the engineering team) that fit your team's workflow. The best tool is the one your team will actually use. Consider where developers already work. If your team lives in GitHub, use GitHub wikis or markdown files in the repo. If you use Jira, leverage Confluence. Reducing context switching increases documentation quality. The idea is to minimize the learning curve for team members.

Look for features that support collaboration. Version control, commenting, and search matter more than fancy formatting. Choose tools that make it easy to keep docs current and find information quickly.