Jimmy on Software

@jimmyonsoftware.com

Software design and AI coding, animated: code that doesn’t break, even when AI writes it. By Jimmy Koppel. Narrated by me (sometimes my AI voice clone). Blog: pathsensitive.com

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In 1999, NASA's $300 million Mars Climate Orbiter program was lost due to a type error. How does a type error destroy a spacecraft?

0 views 21/10/2026

The tech lead says this code is a problem. The engineer says it's fine. It's only ever called right before the benchmark runs. Same code. Why can't they agree? From my essay "The Three Levels of Software": www.pathsensitive.com/2018/01/the-...

0 views 20/10/2026

This code has never failed. Run it all you like, you never see a bug. It's still wrong. How? Based on "The Three Levels of Software," www.pathsensitive.com/2018/01/the-...

0 views 19/10/2026

There are two ways to write bad tests. Most programmers only know one. Test too little, and you miss bugs. But how can a test check too much? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

0 views 18/10/2026

An engineer on my team needed one function from a file in another project. But importing that file would drag in everything else in it too. What could they do? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

0 views 17/10/2026

Want to know what a program can do? Don't look at what it does. You can tell what a kitchen can make without reading a single recipe. So what do you look at? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

0 views 16/10/2026

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In 1999, NASA's $300 million Mars Climate Orbiter program was lost due to a type error. How does a type error destroy a spacecraft?

The tech lead says this code is a problem. The engineer says it's fine. It's only ever called right before the benchmark runs. Same code. Why can't they agree? From my essay "The Three Levels of Software": www.pathsensitive.com/2018/01/the-...

This code has never failed. Run it all you like, you never see a bug. It's still wrong. How? Based on "The Three Levels of Software," www.pathsensitive.com/2018/01/the-...

There are two ways to write bad tests. Most programmers only know one. Test too little, and you miss bugs. But how can a test check too much? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

An engineer on my team needed one function from a file in another project. But importing that file would drag in everything else in it too. What could they do? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

Want to know what a program can do? Don't look at what it does. You can tell what a kitchen can make without reading a single recipe. So what do you look at? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

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Windows had code that checks if you're playing SimCity. SimCity freed memory, then kept using it. That worked on Windows 3 but crashed on Windows 95, so Microsoft gave it a special case. Was that a bug in SimCity? From my essay: www.pathsensitive.com/2018/01/the-...

0 views 11/10/2026

The junior said two days. It took a month. The senior said two weeks. It took two weeks. The ninja said an hour. It took an hour. How? Music: "Ishikari Lore" by Kevin MacLeod (incompetech.com), CC BY 4.0

0 views 11/10/2026

Imagine a microwave that checks you didn't type a negative number. Or that it isn't causing a nuclear reaction. Absurd, right? Yet a lot of code does something morally similar. Why is checking errors bad? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

0 views 12/10/2026

Moving messy code into its own function makes it look cleaner. But is that actually refactoring? Or just boxing? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

0 views 13/10/2026

You are using software right now that has a flaw that will never be fixed In the early '90s, the people writing the HTTP standard misspelled "referrer". Now your browser still sends that typo almost every time you visit a web page. Not even an AI can fix it. Come learn why.

0 views 14/10/2026

Here's a paradox: why are more senior engineers willing to leave more code messy? Is there a deeper wisdom? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

0 views 15/10/2026

Jimmy on Software

Latest videos

In 1999, NASA's $300 million Mars Climate Orbiter program was lost due to a type error. How does a type error destroy a spacecraft?

The tech lead says this code is a problem. The engineer says it's fine. It's only ever called right before the benchmark runs. Same code. Why can't they agree? From my essay "The Three Levels of Software": www.pathsensitive.com/2018/01/the-...

This code has never failed. Run it all you like, you never see a bug. It's still wrong. How? Based on "The Three Levels of Software," www.pathsensitive.com/2018/01/the-...

There are two ways to write bad tests. Most programmers only know one. Test too little, and you miss bugs. But how can a test check too much? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

An engineer on my team needed one function from a file in another project. But importing that file would drag in everything else in it too. What could they do? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

Want to know what a program can do? Don't look at what it does. You can tell what a kitchen can make without reading a single recipe. So what do you look at? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

Popular videos

In 1999, NASA's $300 million Mars Climate Orbiter program was lost due to a type error. How does a type error destroy a spacecraft?

The tech lead says this code is a problem. The engineer says it's fine. It's only ever called right before the benchmark runs. Same code. Why can't they agree? From my essay "The Three Levels of Software": www.pathsensitive.com/2018/01/the-...

This code has never failed. Run it all you like, you never see a bug. It's still wrong. How? Based on "The Three Levels of Software," www.pathsensitive.com/2018/01/the-...

There are two ways to write bad tests. Most programmers only know one. Test too little, and you miss bugs. But how can a test check too much? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

An engineer on my team needed one function from a file in another project. But importing that file would drag in everything else in it too. What could they do? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

Want to know what a program can do? Don't look at what it does. You can tell what a kitchen can make without reading a single recipe. So what do you look at? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

Shorts

In 1999, NASA's $300 million Mars Climate Orbiter program was lost due to a type error. How does a type error destroy a spacecraft?

The tech lead says this code is a problem. The engineer says it's fine. It's only ever called right before the benchmark runs. Same code. Why can't they agree? From my essay "The Three Levels of Software": www.pathsensitive.com/2018/01/the-...

This code has never failed. Run it all you like, you never see a bug. It's still wrong. How? Based on "The Three Levels of Software," www.pathsensitive.com/2018/01/the-...

There are two ways to write bad tests. Most programmers only know one. Test too little, and you miss bugs. But how can a test check too much? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

An engineer on my team needed one function from a file in another project. But importing that file would drag in everything else in it too. What could they do? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

Want to know what a program can do? Don't look at what it does. You can tell what a kitchen can make without reading a single recipe. So what do you look at? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

First videos

Windows had code that checks if you're playing SimCity. SimCity freed memory, then kept using it. That worked on Windows 3 but crashed on Windows 95, so Microsoft gave it a special case. Was that a bug in SimCity? From my essay: www.pathsensitive.com/2018/01/the-...

The junior said two days. It took a month. The senior said two weeks. It took two weeks. The ninja said an hour. It took an hour. How? Music: "Ishikari Lore" by Kevin MacLeod (incompetech.com), CC BY 4.0

Imagine a microwave that checks you didn't type a negative number. Or that it isn't causing a nuclear reaction. Absurd, right? Yet a lot of code does something morally similar. Why is checking errors bad? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

Moving messy code into its own function makes it look cleaner. But is that actually refactoring? Or just boxing? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

You are using software right now that has a flaw that will never be fixed In the early '90s, the people writing the HTTP standard misspelled "referrer". Now your browser still sends that typo almost every time you visit a web page. Not even an AI can fix it. Come learn why.

Here's a paradox: why are more senior engineers willing to leave more code messy? Is there a deeper wisdom? From my booklet "7 Mistakes That Cause Fragile Code": www.mirdin.com/7-mistakes

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