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Code Comments That Actually Help: The Google Engineering Approach

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You have written a brilliant piece of code. It works flawlessly, passes all tests, and solves the problem elegantly. But six months later, you stare at your own creation wondering what you were thinking.

Sound familiar? You're not alone.

Even at Google, where engineering excellence is paramount, the battle against incomprehensible code is ongoing.

The difference between Google engineering teams and most development organizations isn't just their technical prowess. It's their systematic approach to making code understandable through strategic commenting practices.

Let's dive into what makes their approach so effective and how you can apply these principles to boost your team's productivity.

The Hidden Cost of Poor Commenting

Poor code comments aren't just annoying. They are productivity killers. Studies show that developers spend 58% of their time trying to understand existing code rather than writing new features.

At Google, they have recognized that effective commenting isn't just about documentation. It's about maintaining velocity as teams scale.

When your comments fail, several things happen:

  • Onboarding becomes a nightmare - New developers take weeks to understand systems that should be clear in days
  • Bug fixes turn into archeological digs - Simple fixes become complex investigations into intent
  • Code reviews become gatekeeping exercises - Reviewers can't understand the code well enough to provide meaningful feedback
  • Technical debt compounds - Fear of breaking poorly understood code leads to workarounds instead of refactoring

Google's approach addresses these problems systematically.

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Google's Comment Philosophy: The Why Over What

The cornerstone of Google's commenting approach is deceptively simple: comments should explain why, not what.

This principle appears throughout their engineering practices documentation and style guides.

Here's what this looks like in practice:

*// Bad: Describes what the code does// Loop through users and increment counter*
for (let user of users) {
  counter++;
}

*// Good: Explains why this approach was chosen// Count active users for billing calculation// Using simple loop instead of users.length to exclude soft-deleted records*
for (let user of users) {
  if (!user.deletedAt) {
    counter++;
  }
}
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This shift in thinking transforms comments from redundant noise into valuable context that helps future developers (including yourself) make informed decisions.

The Three Types of Comments That Work


Google's engineering teams focus on three specific types of comments that deliver maximum value:

1. Implementation Comments: The Decision Makers

These comments explain non-obvious choices and tricky implementations. They're scattered throughout the code and serve as breadcrumbs for future developers.

def calculate_similarity(text1, text2):
    *# Using Jaccard similarity instead of cosine similarity# because our text samples are typically very short# and Jaccard handles this edge case better*
    return jaccard_distance(text1, text2)
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2. Documentation Comments: The API Contracts

These follow standardized formats and describe what functions, classes, and modules do. They're the public interface documentation.

*/**
 * Calculates user engagement score based on activity patterns.
 * 
 * @param userId The unique identifier for the user
 * @param timeWindow Days to look back for activity (1-365)
 * @return Engagement score between 0.0 and 1.0, where 1.0 indicates
 *         highest engagement. Returns -1.0 if user not found.
 * @throws IllegalArgumentException if timeWindow is outside valid range
 */*
public double calculateEngagementScore(String userId, int timeWindow) {
    *// Implementation details...*
}
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3. Contextual Comments: The Assumption Clarifiers

These comments document assumptions, preconditions, and non-obvious requirements that the code depends on.

*// Assumes user has already been authenticated by middleware// and userId is guaranteed to be valid*
async function getUserPreferences(userId: string) {
    *// Direct database call without validation*
    return await db.preferences.findByUserId(userId);
}
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Google's Comment Quality Standards

Google maintains specific quality standards for comments that go beyond just "write more comments" :

1. Proper Grammar and Punctuation Matter

Comments should read like well-written prose. This isn't pedantry. Clear communication in comments reflects clear thinking about the code.

*# Bad# check if user can access this thing*
if user.hasPermission('read'):

*# Good  # Verify user has read permissions before displaying sensitive data.*
if user.hasPermission('read'):
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2. Explain Magic Numbers and Booleans

When you pass literal values to functions, explain what they represent.

*// Bad*
processPayment(amount, true, 30, null);

*// Good*
processPayment(
    amount,
    true,  *// isRecurring*
    30,    *// retryDays*
    null   *// customHandler*
);
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Update Comments When Code Changes

Outdated comments are worse than no comments. Google's code review process specifically looks for comment accuracy.

The Code Review Integration

Google's commenting success isn't just about writing good comments. It's about integrating comment quality into their code review process.

Their code reviewers specifically look for:

  • Missing context - When code makes assumptions that aren't documented
  • Outdated information - Comments that no longer match the implementation
  • Obvious statements - Comments that just repeat what the code says
  • Missing explanations - Complex logic without accompanying reasoning

This systematic approach ensures that comment quality becomes part of the team culture, not just individual preference.

Implementing Google's Approach in Your Team

You don't need Google's infrastructure to adopt their commenting principles. Here's how to get started:

Start With Comment Standards

Define what deserves comments in your codebase:

  • Complex business logic
  • Performance optimizations
  • Security considerations
  • Integration points with external systems
  • Workarounds for bugs or limitations

Make Comments Part of Your Definition of Done

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Just like tests and documentation, comments should be a requirement for completing features, not an afterthought.

1. Review Comments Like Code

During code reviews, evaluate comments for:

  • Accuracy
  • Necessity
  • Clarity
  • Completeness

2. Use Linting Tools

Implement automated checks for comment standards where possible. Many modern linters can enforce documentation comment formats.

3. Measuring Comment Effectiveness

Google tracks the impact of their commenting practices through developer productivity metrics. You can do the same by monitoring:

  • Code review time - Well-commented code should reduce review cycles
  • Onboarding velocity - New team members should contribute faster
  • Bug resolution time - Clear intent should speed up debugging
  • Refactoring confidence - Teams should be more willing to improve unclear code

Tools That Support Good Commenting

The right tools can make maintaining comment quality easier. Modern development environments offer features that align with Google's approach:

  • IDE integration - Real-time comment linting and formatting
  • Documentation generators - Automatic API documentation from comments
  • Review automation - Bots that flag missing or outdated comments
  • Template systems - Consistent comment structures across projects

This is where tools like Teamcamp become valuable. Rather than just tracking what code was written, Teamcamp helps teams maintain the context , help in Tracking time, Manage Clients also around why code was written.

Build your team's knowledge hub with Teamcamp →

By capturing decision-making processes and linking them to code changes, it creates a comprehensive knowledge base that complements good commenting practices.

When your comments explain the immediate why, Teamcamp preserves the broader context of project decisions and team discussions.

Beyond Comments: Building Documentation Culture

Great comments are just one piece of the documentation puzzle. Google's approach extends to creating a culture where knowledge sharing is prioritized.

This includes:

  • Regular documentation reviews - Scheduled time to update and improve comments
  • Knowledge sharing sessions - Team discussions about complex code sections
  • Documentation ownership - Clear responsibility for maintaining different code areas
  • Learning from mistakes - Retrospectives that identify documentation gaps

The goal isn't perfect documentation. It's sustainable documentation that grows with your codebase and supports your team's long-term productivity.

The Productivity Impact

Teams that adopt Google's commenting approach typically see measurable improvements in developer productivity within months. The initial investment in establishing standards and training pays dividends through:

  • Faster code reviews
  • Reduced debugging time
  • Smoother knowledge transfer
  • Higher code quality
  • Better team collaboration

Your future self will thank you for taking the time to write comments that actually help. More importantly, your teammates will be able to build on your work instead of deciphering it.

The difference between good developers and great developers isn't just the code they write. It's how well they communicate the thinking behind that code. Google's commenting approach provides a proven framework for making that communication effective, sustainable, and valuable to your entire development team.

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