Debug an Error Message Step-by-Step

This prompt converts a confusing error into a methodical debugging session: plain-English explanation, ranked root causes, a concrete check for each, then the fix. Reach for it when you're stuck on an error you don't recognize and want a diagnosis path rather than a blind guess. The ranked-causes-plus-tests structure stops the model from confidently proposing one wrong fix and instead has you verify before you change anything.

What you can expect back

What the error means
'Cannot read properties of undefined (reading map)' means you called .map on something that is undefined. At ProductList.tsx:14, `data.products` is undefined at the moment of render.

Most likely causes (ranked)
1. Render happens before the query resolves — on first render `data` is undefined, so `data.products` throws. (Most likely.)
2. The API returns a shape without a top-level `products` key (e.g. the array is the root, or nested differently).
3. fetchProducts throws/returns undefined, leaving the query with no data.

Checks
1. Add `console.log(data)` above the return. If it logs `undefined` first then the object, it's the loading race.
2. Inspect the network response body — confirm it actually has a `products` field.
3. Log inside fetchProducts to confirm it returns and what it returns.

Likely fix (cause 1)
Guard the loading/empty state:
`const { data, isLoading } = useQuery(...);`
`if (isLoading || !data) return <Spinner />;`
Then map over `data.products ?? []`.

Illustrative example — your results will vary by tool and inputs.

Get sharper results

• 01Paste the complete stack trace, not just the top line — the call chain often points at the real origin several frames down from where the error surfaces.
• 02Mention what you already tried and what changed right before the error appeared; it lets the model rule out causes instead of repeating your steps.
• 03Include version numbers in the language/framework field, since the same error can have different causes across major versions of a library.
• 04If the error is intermittent, say so explicitly — it shifts the ranked causes toward race conditions, caching, and environment differences.
• 05After you run the suggested checks, paste the results back and ask it to re-rank; the second pass is usually where the real fix lands.

Adapt it for your case