# **Low-Level Design (LLD) Template**

**Document Revision History**

| Ver No | Date | Change Information | Author | Approver |
|--------|------|--------------------|--------|----------|
| V1.0 | Date | Initial Draft | Author Name | Approver Name |


### **1. Problem Statement**

- Clearly describe the problem in 2–3 lines
- Mention what needs to be achieved and why

**Example:**

Admin dashboard should display the count of pending transfers so that operations team can monitor incomplete transactions and take timely action.

### **2. Scope**
- What is included
- What is excluded (if any)

### **3. Solution Approach (Technical Design)**
#### **3.1 Overview**
- High-level explanation of the solution
- **Mention whether:**
    - Existing services will be reused
    - New services/APIs will be created
    - Existing services will be enhanced

#### **3.2 Components / Modules Involved**
- **List all impacted modules:**
    - Backend services
    - Frontend/UI
    - Database
    - External integrations (if any)

#### **3.3 API Design**
- **For each API:**
    - **API Name:**
    - **Method**: (GET/POST/PUT/DELETE)
    - **Endpoint:**
    - **Request**:
    - **Response**:
    - **Auth Required:** Yes/No
    - **Service Handling It:**

#### **3.4 Data Flow**
- Step-by-step flow of how data moves across systems
- **Mention**:
    - Source of data
    - Processing logic
    - Final output

#### **3.5 Database Impact**
- New tables (if any)
- Changes in existing tables
- New fields/columns
- Indexing (if needed)
- Query changes

#### **3.6 Business Logic**
- Core logic/conditions
- Rules to calculate/derive values

**Example:**

Pending transfer = transactions where status IN (initiated, processing, on-hold)

#### **3.7 Service Design**
- Number of services impacted/added
- **Description of each:**
    - New service
    - Modified service
    - Reusable service

#### **3.8 Error Handling**
- Failure scenarios
- Retry mechanisms
- Logging strategy
- User-facing error messages

#### **3.9 Edge Cases**
- List all possible edge cases
**Example:**
- Transfer stuck due to insufficient liquidity
- Partial transaction completion
- Duplicate requests

#### **3.10 Performance Considerations**
- Query optimization
- Caching (if required)
- Pagination / batching
- Expected load

#### **3.11 Security Considerations**
- Authentication / Authorization
- Data masking (if applicable)
- Sensitive data handling

### **4. Sequence Diagram**
- Visual flow of request → processing → response
- **Must include:**
    - UI
    - Backend service(s)
    - DB
    - External systems (if any)

### **5. Unit Test Criteria**
- Define test scenarios:
**Example:**
- Valid pending transfers count
- No data scenario
- Error response handling
- Edge case validation

### **6. Integration / QA Test Scenarios**
- End-to-end scenarios
- APIUI validation

### **7. Dependencies**
- External services
- Other modules
- Data availability

### **8. Assumptions**
- Any assumptions made during design

### **9. Risks & Mitigation**
- Potential risks
- How to handle them

### **10. Deployment / Rollout Plan**
- Any migration required
- Backward compatibility
- Feature flag (if needed)

### **11. Open Questions**
- Any pending clarifications