Home > Store

Code That Fits in Your Head: Heuristics for Software Engineering

Register your product to gain access to bonus material or receive a coupon.

Code That Fits in Your Head: Heuristics for Software Engineering

Best Value Purchase

Book + eBook Bundle

  • Your Price: $43.19
  • List Price: $71.98
  • Includes EPUB and PDF
  • About eBook Formats
  • This eBook includes the following formats, accessible from your Account page after purchase:

    ePub EPUB The open industry format known for its reflowable content and usability on supported mobile devices.

    Adobe Reader PDF The popular standard, used most often with the free Acrobat® Reader® software.

    This eBook requires no passwords or activation to read. We customize your eBook by discreetly watermarking it with your name, making it uniquely yours.

More Purchase Options


  • Your Price: $31.99
  • List Price: $39.99
  • Usually ships in 24 hours.

eBook (Watermarked)

  • Your Price: $25.59
  • List Price: $31.99
  • Includes EPUB and PDF
  • About eBook Formats
  • This eBook includes the following formats, accessible from your Account page after purchase:

    ePub EPUB The open industry format known for its reflowable content and usability on supported mobile devices.

    Adobe Reader PDF The popular standard, used most often with the free Acrobat® Reader® software.

    This eBook requires no passwords or activation to read. We customize your eBook by discreetly watermarking it with your name, making it uniquely yours.



  • Actionable advice for writing code at a sustainable pace and creating sustainable code basesby the author of the Humane Code series at Robert C. Martin's cleancoders.com
  • Helps developers rein in coplexity to build great software within budget and resource constraints
  • Packed with C# code examples and accompanied by a comprehensive sample application code base organized in a Git repository
  • Carefully written to serve developers working with any object-oriented enterprise language: C#, Java, and beyond
  • The latest title in Addison Wesley's renowned Robert C. Martin Series on better software development


  • Copyright 2022
  • Dimensions: 7" x 9-1/8"
  • Pages: 416
  • Edition: 1st
  • Book
  • ISBN-10: 0-13-746440-1
  • ISBN-13: 978-0-13-746440-1

How to Reduce Code Complexity and Develop Software More Sustainably

"Mark Seemann is well known for explaining complex concepts clearly and thoroughly. In this book he condenses his wide-ranging software development experience into a set of practical, pragmatic techniques for writing sustainable and human-friendly code. This book will be a must-read for every programmer."
--Scott Wlaschin, author of Domain Modeling Made Functional
Code That Fits in Your Head offers indispensable, practical advice for writing code at a sustainable pace and controlling the complexity that causes projects to spin out of control.

Reflecting decades of experience helping software teams succeed, Mark Seemann guides you from zero (no code) to deployed features and shows how to maintain a good cruising speed as you add functionality, address cross-cutting concerns, troubleshoot, and optimize. You'll find valuable ideas, practices, and processes for key issues ranging from checklists to teamwork, encapsulation to decomposition, API design to unit testing.

Seemann illuminates his insights with code examples drawn from a complete sample project. Written in C#, they're designed to be clear and useful to anyone who uses any object-oriented language including Java , C++, and Python. To facilitate deeper exploration, all code and extensive commit messages are available for download.
  • Choose mindsets and processes that work, and escape bad metaphors that don't
  • Use checklists to liberate yourself, improving outcomes with the skills you already have
  • Get past analysis paralysis by creating and deploying a vertical slice of your application
  • Counteract forces that lead to code rot and unnecessary complexity
  • Master better techniques for changing code behavior
  • Discover ways to solve code problems more quickly and effectively
  • Think more productively about performance and security
If you've ever suffered through bad projects or had to cope with unmaintainable legacy code, this guide will help you make things better next time and every time.

Register your book for convenient access to downloads, updates, and/or corrections as they become available. See inside book for details.



Please register your book to gain access to the source code download files for this book.


Author's Site

Please visit the author's site at https://blog.ploeh.dk/.

Sample Content

Online Sample Chapter

How to Troubleshoot Code


Code That Fits in Your Head: Foreword

Method Naming in API Design

Software System Logging

The Science of Test-Driven Development

Sample Pages

Download the sample pages (includes Chapter 12)

Bibliography (81 KB .pdf)

Table of Contents

Series Editor Foreword xix
Preface xxiii
About the Author xxix

Part I: Acceleration 1

Chapter 1: Art or Science? 3

1.1 Building a House 4
1.2 Growing a Garden 7
1.3 Towards Engineering 8
1.4 Conclusion 14

Chapter 2: Checklists 15
2.1 An Aid to Memory 15
2.2 Checklist for a New Code Base 17
2.3 Adding Checks to Existing Code Bases 29
2.4 Conclusion 32

Chapter 3: Tackling Complexity 33
3.1 Purpose 34
3.2 Why Programming Is Difficult 38
3.3 Towards Software Engineering 44
3.4 Conclusion 46

Chapter 4: Vertical Slice 49
4.1 Start with Working Software 50
4.2 Walking Skeleton 53
4.3 Outside-in 60
4.4 Complete the Slice 77
4.5 Conclusion 85

Chapter 5: Encapsulation 87
5.1 Save the Data 87
5.2 Validation 92
5.3 Protection of Invariants 105
5.4 Conclusion 108

Chapter 6: Triangulation 111
6.1 Short-Term versus Long-Term Memory 111
6.2 Capacity 114
6.3 Conclusion 127

Chapter 7: Decomposition 129
7.1 Code Rot 129
7.2 Code That Fits in Your Brain 136
7.3 Conclusion 153

Chapter 8: API Design 155
8.1 Principles of API Design 156
8.2 API Design Example 168
8.3 Conclusion 176

Chapter 9: Teamwork 177
9.1 Git 178
9.2 Collective Code Ownership 187
9.3 Conclusion 199

Part II: Sustainability 201

Chapter 10: Augmenting Code 203

10.1 Feature Flags 204
10.2 The Strangler Pattern 209
10.3 Versioning 218
10.4 Conclusion 220

Chapter 11: Editing Unit Tests 223
11.1 Refactoring Unit Tests 223
11.2 See Tests Fail 233
11.3 Conclusion 234

Chapter 12: Troubleshooting 235
12.1 Understanding 235
12.2 Defects 240
12.3 Bisection 250
12.4 Conclusion 255

Chapter 13: Separation of Concerns 257
13.1 Composition 258
13.2 Cross-Cutting Concerns 267
13.3 Conclusion 274

Chapter 14: Rhythm 275
14.1 Personal Rhythm 276
14.2 Team Rhythm 282
14.3 Conclusion 285

Chapter 15: The Usual Suspects 287
15.1 Performance 288
15.2 Security 292
15.3 Other Techniques 300
15.4 Conclusion 308

Chapter 16: Tour 309
16.1 Navigation 309
16.2 Architecture 318
16.3 Usage 323
16.4 Conclusion 326

Appendix A: List of Practices 329
A.1 The 50/72 Rule 329
A.2 The 80/24 Rule 330
A.3 Arrange Act Assert 330
A.4 Bisection 330
A.5 Checklist for A New Code Base 331
A.6 Command Query Separation 331
A.7 Count the Variables 331
A.8 Cyclomatic Complexity 331
A.9 Decorators for Cross-Cutting Concerns 332
A.10 Devil's Advocate 332
A.11 Feature Flag 332
A.12 Functional Core, Imperative Shell 333
A.13 Hierarchy of Communication 333
A.14 Justify Exceptions from the Rule 333
A.15 Parse, Don't Validate 334
A.16 Postel's Law 334
A.17 Red Green Refactor 334
A.18 Regularly Update Dependencies 335
A.19 Reproduce Defects as Tests 335
A.20 Review Code 335
A.21 Semantic Versioning 335
A.22 Separate Refactoring of Test and Production Code 335
A.23 Slice 336
A.24 Strangler 336
A.25 Threat-Model 337
A.26 Transformation Priority Premise 337
A.27 X-driven Development 337
A.28 X Out Names 338

Bibliography 339
Index 349


Submit Errata

More Information

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020