Vibe Coding Errors: What the Red Messages Really Mean
Most vibe coding errors are a handful of standard messages, and you do not have to understand them to get them fixed. Copy the first red line, say what you were doing when it appeared, and ask your AI to show you the cause.
Where do you find the red message?
If your game runs in a browser, it sits in the console, a hidden panel where the browser writes down what went wrong. In Chrome, press Ctrl + Shift + J on Windows or Linux, or Cmd + Option + J on a Mac. Red lines are errors.
Read the first red line, not the last. One fault often sets off a whole cascade, and the later lines are usually just knock-on effects.
What do the messages mean?
| The message says | In plain words | Often happens when |
|---|---|---|
Cannot read properties of undefined (reading 'hp') |
The game reached for something that is not there. Here it wanted the health of a thing that does not exist | An enemy was removed, but something still aims at it |
x is not defined |
The game used a name that was never set up, or a helper was not loaded yet | The AI renamed or moved something and missed one spot |
Maximum call stack size exceeded |
Something keeps calling itself and never stops | Two parts of the game keep setting each other off |
A message with CORS and file:/// |
The browser refuses to load the game's files from your disk | You double-clicked the game file instead of starting it through a small local server |
Unexpected token |
The code has a typo the browser cannot read | An edit stopped halfway through a file |
Those are the common readings, not a diagnosis. The same words can come from different causes in your project.
Why does it matter what you were doing?
The message says what failed, not when or why. Say you are making Kettle Keep, an invented game where steam turrets defend a teapot. On wave 3 the game freezes with Cannot read properties of undefined (reading 'hp').
If you paste only that line, your AI may guess, and a common guess is to wrap the line so that the error stops showing. The red line goes away, and the turret quietly stops firing.
Now add one sentence: "It happens on wave 3, just after the last goblin near a turret dies." That points to a turret still aiming at a goblin that is gone. The real fix is to pick a new target, and your turrets keep working.
If the fault has no red line at all, look at bugs your AI will not see instead.
Paste this to your AI
My game shows an error. Here is the first red line from the console, copied exactly:
[paste the line]
What I was doing when it appeared: [one sentence]
How often it happens: [every time / sometimes / once]
Do not change anything yet. Tell me in plain words what the message means. Then draw what is supposed to happen at that moment, step by step, as a small Mermaid diagram, and mark the step where the real game leaves it. Show me that exact place in my project, with the line quoted. If several places could be the cause, list them and say what would tell them apart.
If you cannot tell from this, say "I do not know yet" and tell me what you need, such as something to try in the game or a temporary message that shows you more.
Fix the cause, not the message. Do not hide or silence the error. Then tell me what you tried and what the console showed afterwards.
Or skip this and connect the MCP: your AI then finds all of this by itself.Connect the MCP
How to check it worked
- Do the same thing again. Repeat exactly what caused it. The red line should be gone.
- Check that the feature still works. A vanished message is not a fix. In the example, the turrets must still fire.
- Keep the console open for a whole round. Play from start to finish and watch for new red lines.
- Look at the marked step. The drawing should match what you saw in the game. Ask for the cause in one sentence too. If your AI cannot say what was wrong and why it no longer happens, the fault may only be hiding.
- Reload and try twice more. Errors that come and go often survive one lucky try.