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AI / Coding and Debugging

Locate the error

Causes ranked by likelihood, plus how to verify each one

I hit this error on [stack and version]. [What I have already tried]. Please: 1) list the causes from most to least likely; 2) for each, give a way to verify it (one command, or a minimal reproduction); 3) do not repeat anything I have already tried; 4) if there is not enough information to decide, tell me exactly what to add.

```
[paste the error and stack trace]
```

How to use

Paste the error and the stack first, before the code — the code pulls the guess toward whatever it can see.

Good for

The error reproduces reliably and the stack trace is complete, but you do not know the framework or library layer it fails in.
Two or three fixes have already failed and you need help ruling directions out, not more guesses.

Not for

The error is intermittent in production and the logs carry no request id or input parameters: add logging first, or you will only get a list of guesses.
It was actually caused by the lines you just changed: git diff or git bisect beats asking a model.

Example

Input

TypeError: Cannot read properties of undefined (reading 'map')
    at OrderList (src/components/OrderList.tsx:42:31)
    at renderWithHooks (react-dom.development.js:14985:18)

Next.js 13.4 / SWR 2.2 / Node 18
Already tried: adding ?., clearing the .next cache, reinstalling node_modules

What you get

Rank 'the component calls data.map while the API is still loading or has errored, so data is undefined' first; second, SWR has no fallbackData and the key is reused across route changes; third, the endpoint itself returns empty. Give each one a verification step (log data before line 42, mock a 500 and see if it still crashes) and skip the `?.` already tried.

Common mistakes

Pasting only the last error line without the stack or versions: it can only guess from the most popular framework version.
Omitting what you already tried, so it walks the same ruled-out paths again and the round is wasted.

Try tweaking it like this

Add 'first give only the three most likely causes and the command that confirms each, no fix code yet' to narrow the search before editing.
Paste the actual `package.json` or `pip freeze` text instead of a version summary; most version-related hallucination disappears.

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