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Computer Science & Algorithms

Zawinski's Law

Model #0678Category: Computer Science & AlgorithmsSource: Jamie ZawinskiDepth to apply:
4 min read

On this page

  • Core Idea
  • How to See It
  • How to Use It
  • Founders & Leaders
  • Connected Models
  • One Key Quote
  • Summary & Further Reading

Contents

  1. 1. Core Idea
  2. 2. How to See It
  3. 3. How to Use It
  4. 4. Founders & Leaders
  5. 5. Connected Models
  6. 6. One Key Quote
  7. 7. Summary & Further Reading
·Computer Science & Algorithms
Section 1

Core Idea

Zawinski's law (Jamie Zawinski, Netscape/Mozilla): "Every program attempts to expand until it can read mail. Those programs which cannot so expand are replaced by ones that can." The joke is that successful software accretes features—email, chat, calendaring—until it becomes a platform. The serious point: feature creep and scope expansion are the default; programs that stay focused are the exception and often get displaced by ones that do more. It's a warning: without discipline, "one more feature" wins and complexity compounds. Building & scaling: the pull toward becoming everything is strong; resisting it is a design choice.
Section 2

How to See It

Building & Scaling
You're seeing Zawinski's Law when a product or system that started with a clear purpose keeps adding capabilities (messaging, notifications, integrations) until the core job is buried under scope. The program "expands until it can read mail."
Section 3

How to Use It

Treat scope expansion as the default. Actively resist: define the minimal job, say no to "and also," and split into smaller programs or services when one tool is doing too much. Prefer composition (small tools that work together) over one mega-app. In product: guardrails (roadmap discipline, "one thing" positioning) counter the law.
Decision filter
"Is this feature necessary for the core job, or are we expanding until we can read mail? If the latter, consider a separate tool or saying no; keep the program focused."
As a founder
Product and roadmap drift follow Zawinski's law: the temptation is to add messaging, workflow, analytics—until the product is everything. Resist by defining the one job and refusing scope that doesn't serve it. Compose with other tools instead of absorbing their functions.
Section 5

Founders & Leaders

Marc AndreessenCo-founder, Netscape; co-founder, a16z
Andreessen was at Netscape when Zawinski formulated the law—they lived the tension between focused software and "expand until it can read mail." Andreessen later backed companies that chose focus (e.g. single-use tools) and those that became platforms. Founders can take the lesson: expansion is the default; focus is a choice. Decide explicitly whether you're building one thing well or a platform, and structure accordingly.
Section 7

Connected Models

Reinforces
Gall's Law
Gall's law: complex systems that work evolved from simple systems that worked. Zawinski's law is the failure mode: adding features before the core works. Resist Zawinski by obeying Gall—get the simple thing right first.
Tension
Modularity
Modularity says: split into coherent pieces. Zawinski's law says: one program tends to absorb more. The tension: modularity (separate mail reader, chat, calendar) is the antidote; one app that does everything is the law in action.
Leads-to
Technical Debt
Feature creep adds code paths, dependencies, and edge cases—technical debt. Zawinski's law predicts that creep; debt is the accumulated cost. Controlling scope controls debt.
Section 8

One Key Quote

"Every program attempts to expand until it can read mail." The rest of the law: those that don't expand get replaced by ones that do. A caution against unchecked scope.
— Jamie Zawinski (attributed)
Section 11

Summary & Further Reading

Zawinski's law: programs tend to expand in scope until they do everything (including "read mail"); focused programs get replaced by expanders. Treat expansion as the default; resist with focus, modularity, and composition.
01
The Cathedral and the Bazaar — Eric S. Raymond
Essay
On Unix philosophy and the value of small, composable tools—the opposite of Zawinski's expansion.
02
Gall's Law — FTN
Internal
Start simple; Zawinski's law is what happens when you don't.
03
Technical Debt — FTN
Internal
Scope creep and feature accumulation as a source of debt.

Why this matters next

mental modelsTechnical Debt

Zawinski's Law applied the Technical Debt mental model

mental modelsModularity

Zawinski's Law applied the Modularity mental model

mental modelsAlgorithms

Zawinski's Law applied the Algorithms mental model

mental modelsCost

Zawinski's Law applied the Cost mental model

mental modelsPositioning

Zawinski's Law applied the Positioning mental model

mental modelsGall's Law

Zawinski's Law applied the Gall's Law mental model

Frequently asked questions

What is Zawinski's Law?+

Zawinski's Law is a mental model used for better thinking and decision-making.

How do you apply Zawinski's Law?+

To apply Zawinski's Law, identify situations where this framework is relevant, then use it as a lens to evaluate your options and decisions. The model is most useful when combined with other complementary mental models.

What category does Zawinski's Law fall under?+

Zawinski's Law falls under the Computer Science & Algorithms category of mental models. Other models in this category can be found on the Computer Science & Algorithms hub page.

Why is Zawinski's Law important?+

Zawinski's Law is important because it provides a structured way to think about problems that would otherwise be approached with intuition alone. Understanding this model helps you avoid common reasoning errors and make better decisions.

Where does Zawinski's Law come from?+

Zawinski's Law is discussed in the tradition of Jamie Zawinski.

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On this page

  • Core Idea
  • How to See It
  • How to Use It
  • Founders & Leaders
  • Connected Models
  • One Key Quote
  • Summary & Further Reading

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