Got it—do you want a template you can drop into a repo, or a concrete example to flesh out a specific use-case? Here are both, plus a tidy starting point you can adapt.

Option A: Practical template for a use-case solution
- Title
  - Short, descriptive name of the use-case.
- Summary
  - One or two sentences on what problem is solved and the high-level approach.
- Actors
  - List all roles that interact with the system (e.g., Customer, Admin, Payment Gateway, Inventory Service).
- Preconditions
  - What must be true before the use-case starts (e.g., user is authenticated, cart exists).
- Postconditions / Success Criteria
  - What must be true after the use-case completes (e.g., order created, inventory decremented, payment confirmed).
- Triggers
  - What event starts the use-case (e.g., user clicks “Checkout”).
- Main Flow (Basic Path)
  - Step-by-step sequence of actions from start to finish.
- Alternative Flows
  - Variations or exceptions (e.g., payment failure, out-of-stock item, cart abandoned).
- Non-functional Requirements
  - Performance, reliability, security, accessibility, compliance notes.
- Assumptions
  - Any assumptions about data, integrations, or environment.
- Data Model (core entities)
  - Key entities and their relationships (e.g., Customer, Cart, Order, Payment, Inventory).
- Interfaces / APIs
  - External or internal services involved (endpoints, contracts, and data formats).
- UI/UX Considerations
  - Key screens, messaging, error handling, and accessibility notes.
- Compliance & Auditing
  - Logs, traceability, privacy considerations if relevant.
- Testing & Validation
  - Suggested test cases, acceptance criteria, and edge cases.
- Metrics & Success Criteria
  - How you’ll measure success (e.g., checkout completion rate, time-to-pay, cart-to-order conversion).
- Risks & Mitigations
  - Potential blockers and mitigation strategies.
- Example Scenario (optional)
  - A concrete walkthrough with sample data to illustrate the flow.

Option B: Concrete example you can adapt
Use-case: Online bookstore checkout

- Title
  - Online Bookstore Checkout
- Summary
  - A customer reviews cart, selects shipping, pays, and receives an order confirmation; system updates inventory and triggers shipment.
- Actors
  - Customer, Payment Gateway, Inventory Service, Shipping Service, Notification Service, Fraud Check Service (optional)
- Preconditions
  - User is authenticated; cart contains at least one item; payment method on file or provided at checkout.
- Postconditions / Success Criteria
  - Order record created; payment captured/authorized; inventory updated; shipping label generated; customer notified.
- Triggers
  - Customer clicks “Checkout” or “Place Order.”
- Main Flow
  1. Customer reviews cart and proceeds to checkout.
  2. System validates cart, stock, and shipping address.
  3. System presents payment options; customer selects method.
  4. Payment gateway processes payment (authorize or capture).
  5. If payment succeeds:
     - Create order record with line items and totals.
     - Reserve and decrement inventory.
     - Create shipping order; generate label.
     - Notify customer of order confirmation and ETA.
  6. If payment fails:
     - Return to checkout with error message; offer retry.
- Alternative Flows
  - Out-of-stock: notify user, offer backorder or alternative.
  - Payment declined: prompt for other method or retry.
  - Address verification failure: request corrected address.
  - Fraud check flag: require additional verification before proceeding.
- Non-functional Requirements
  - Response time: checkout page ≤ 2 seconds; payment processing within 5 seconds.
  - Security: PCI-compliant handling; tokenization; TLS; least privilege access.
  - Fault tolerance: idempotent order creation; retry-safe inventory updates.
- Assumptions
  - Inventory and payment services are available with agreed SLAs.
- Data Model (core)
  - Customer, Cart, CartItem, Product, Order, OrderLine, Payment, Shipment, Inventory
- Interfaces / APIs
  - Payment Gateway API (authorize, capture, refund)
  - Inventory Service (reserve, decrement)
  - Shipping Service (createShipment, track)
  - Notification Service (email/SMS)
- UI/UX Considerations
  - Clear progress indicators; inline validation; error summaries; accessible (ARIA).
- Compliance & Auditing
  - Order events are logged; audit trail for payments; data minimization on UI.
- Testing & Validation
  - Functional tests for each flow; end-to-end checkout test; load test for concurrent checkouts; security tests for data in transit.
- Metrics & Success Criteria
  - Checkout conversion rate, average order value, payment success rate, time-to-complete checkout.
- Risks & Mitigations
  - Payment gateway downtime: have a fallback payment method; retries with backoff.
  - Inventory race conditions: use inventory reservation with idempotent operations.
- Example Scenario
  - User: Alex buys 2 books, uses saved card; payment authorized; order created; inventory updated; shipping label generated; confirmation email sent.

Option C: Repo-friendly structure (use-case driven)
If you’re organizing a code/doc repo, you can structure it like:
- solutions/
  - use-case/
    - ecommerce-checkout/
      - README.md (the template above filled in)
      - architecture.md
      - data-model.md
      - api-contracts/
        - payment-gateway.yaml
        - inventory-service.yaml
      - flows/
        - main-flow.md
        - alt-flows.md
      - tests/
        - test-case-list.md
      - diagrams/
        - sequence-diagram.drawio (or .png)
      - UI/
        - wireframes.pdf
    - user-registration/
      - (same substructure for a different use-case)
    - supply-chain-tracking/
      - ...

If you want, I can tailor the template to a specific domain (e.g., SaaS onboarding, healthcare intake, IoT device provisioning) or fill in a ready-to-copy Markdown file for you. Could you share:
- The domain or the use-case you’re targeting?
- Do you want a ready-to-paste template, or a full example?
- Any constraints (format, diagram preferences, tooling you use)?