Bird
Raised Fist0
LLDsystem_design~25 mins

Code review checklist for LLD - System Design Exercise

Choose your learning style10 modes available

Start learning this pattern below

Jump into concepts and practice - no test required

or
Recommended
Test this pattern10 questions across easy, medium, and hard to know if this pattern is strong
Design: Code Review Checklist for Low-Level Design (LLD)
Focus on reviewing low-level design diagrams and documents. Out of scope: code syntax, high-level architecture, deployment details.
Functional Requirements
FR1: Ensure design correctness and completeness
FR2: Verify adherence to design principles and patterns
FR3: Check for scalability and performance considerations
FR4: Validate modularity and separation of concerns
FR5: Confirm clarity and maintainability of design
FR6: Identify potential security and error handling gaps
FR7: Ensure consistency with overall system architecture
Non-Functional Requirements
NFR1: Checklist must be applicable to designs of varying complexity
NFR2: Must be easy to use by both junior and senior engineers
NFR3: Should cover both functional and non-functional aspects
NFR4: Checklist items must be clear and actionable
Think Before You Design
Questions to Ask
❓ Question 1
❓ Question 2
❓ Question 3
❓ Question 4
❓ Question 5
❓ Question 6
❓ Question 7
Key Components
Class and object diagrams
Sequence and interaction diagrams
Data models and schemas
Interfaces and APIs
Error handling mechanisms
Security controls
Performance optimization techniques
Design Patterns
Single Responsibility Principle
Open/Closed Principle
Factory and Builder patterns
Observer and Strategy patterns
Layered architecture
Dependency Injection
Fail-safe and retry mechanisms
Reference Architecture
 +---------------------+       +---------------------+       +---------------------+
 |  Design Document     | ----> |  Review Checklist    | ----> |  Feedback & Updates  |
 +---------------------+       +---------------------+       +---------------------+
Components
Design Document
LLD diagrams and documents
Contains detailed low-level design including classes, methods, and interactions
Review Checklist
Structured checklist template
Guides reviewers through key design aspects to verify correctness and quality
Feedback & Updates
Collaboration tools (e.g., comments, issue trackers)
Captures review feedback and tracks design improvements
Request Flow
1. Designer creates or updates the low-level design document.
2. Reviewer uses the checklist to systematically evaluate the design.
3. Reviewer notes issues or suggestions based on checklist items.
4. Feedback is communicated back to the designer.
5. Designer revises the design accordingly.
6. Cycle repeats until design meets quality standards.
Database Schema
Not applicable as this is a process checklist rather than a data-driven system.
Scaling Discussion
Bottlenecks
Checklist becomes too long or complex, reducing usability.
Inconsistent application of checklist by different reviewers.
Difficulty in tracking feedback and design iterations at scale.
Solutions
Prioritize checklist items to focus on critical design aspects.
Provide training and examples to standardize review approach.
Use integrated collaboration tools to manage feedback and version control.
Interview Tips
Time: Spend 10 minutes explaining the checklist purpose and key items, 15 minutes walking through example review scenarios, and 5 minutes discussing scaling and tooling.
Importance of systematic design review to catch issues early.
Balancing thoroughness with usability in checklist design.
How checklist supports maintainability, scalability, and security.
Role of collaboration and feedback in improving designs.
Adapting checklist for different project sizes and teams.

Practice

(1/5)
1. Which of the following is the MOST important focus when reviewing a Low-Level Design (LLD) document?
easy
A. Clarity and correctness of the design
B. The color scheme of the document
C. The number of pages in the document
D. The font style used

Solution

  1. Step 1: Understand the purpose of LLD review

    The main goal is to ensure the design is clear and correct so developers can implement it properly.
  2. Step 2: Evaluate options based on relevance

    Options A, B, and D relate to formatting, which is less critical than clarity and correctness.
  3. Final Answer:

    Clarity and correctness of the design -> Option A
  4. Quick Check:

    Focus on clarity and correctness = C [OK]
Hint: Focus on design clarity and correctness first [OK]
Common Mistakes:
  • Focusing on document style over content
  • Ignoring correctness for aesthetics
  • Confusing LLD with high-level design
2. Which checklist item should be included to ensure modularity in an LLD review?
easy
A. Ensure the document has a table of contents
B. Check if the design uses consistent variable names
C. Count the total number of classes
D. Verify if components have clear, single responsibilities

Solution

  1. Step 1: Understand modularity in design

    Modularity means breaking the system into parts that each do one thing well.
  2. Step 2: Match options to modularity

    Verify if components have clear, single responsibilities directly relates to single responsibility, a key modularity principle. Others are unrelated.
  3. Final Answer:

    Verify if components have clear, single responsibilities -> Option D
  4. Quick Check:

    Modularity = single responsibility components [OK]
Hint: Look for single responsibility to ensure modularity [OK]
Common Mistakes:
  • Confusing naming consistency with modularity
  • Counting classes without checking responsibilities
  • Focusing on document formatting
3. Given this checklist item: "Ensure all public methods have clear input and output definitions." What is the MOST likely outcome if this is NOT followed?
medium
A. Developers may implement methods incorrectly due to unclear contracts.
B. The system will automatically generate method documentation.
C. The code will run faster.
D. The design will have fewer classes.

Solution

  1. Step 1: Understand the role of input/output definitions

    Clear definitions guide developers on how to use methods correctly.
  2. Step 2: Analyze consequences of missing definitions

    Without clear contracts, developers may misunderstand method usage, causing errors.
  3. Final Answer:

    Developers may implement methods incorrectly due to unclear contracts. -> Option A
  4. Quick Check:

    Unclear method contracts = incorrect implementation [OK]
Hint: Clear method contracts prevent implementation errors [OK]
Common Mistakes:
  • Assuming code runs faster without definitions
  • Thinking documentation is auto-generated
  • Confusing method count with clarity
4. You find a design where security considerations are missing in the LLD. What is the BEST immediate action during the code review?
medium
A. Approve the design since security is handled later.
B. Ignore security as it is not part of LLD.
C. Request adding security checks and data validation in the design.
D. Suggest removing modularity to simplify security.

Solution

  1. Step 1: Recognize importance of security in LLD

    Security should be considered early to avoid costly fixes later.
  2. Step 2: Choose action that improves design quality

    Requesting security checks and validation ensures design is robust and safe.
  3. Final Answer:

    Request adding security checks and data validation in the design. -> Option C
  4. Quick Check:

    Missing security = request additions [OK]
Hint: Always include security early in design reviews [OK]
Common Mistakes:
  • Ignoring security until later stages
  • Approving incomplete designs
  • Removing modularity harms security
5. During a code review for a complex LLD, you notice the design lacks scalability considerations and testability is weak. Which combined checklist items should you prioritize to improve the design?
hard
A. Increase code comments and skip testing details.
B. Add modular components with clear interfaces and include unit test plans.
C. Focus only on UI design and ignore backend scalability.
D. Reduce the number of classes and remove error handling.

Solution

  1. Step 1: Identify key improvements for scalability and testability

    Modular components with clear interfaces help scale and isolate parts for testing.
  2. Step 2: Match checklist items to these improvements

    Including unit test plans ensures testability is addressed alongside modularity.
  3. Final Answer:

    Add modular components with clear interfaces and include unit test plans. -> Option B
  4. Quick Check:

    Modularity + testing plans = better scalability and testability [OK]
Hint: Combine modularity and testing for scalable, testable design [OK]
Common Mistakes:
  • Removing error handling weakens design
  • Ignoring backend scalability
  • Focusing only on comments without tests