---

name: error-decoder
description: "Decode an error message or stack trace into a plain-English cause, the exact fix, and how to prevent it. Use when asked to explain an error, debug a stack trace, figure out why code is throwing, or make sense of a cryptic exception. Produces a structured diagnosis: what the error means, the most likely cause, a concrete fix with code, and a prevention tip."

Error Decoder Skill

Turn a scary error into a clear answer — the way a senior engineer would read it over your shoulder.

Working from a brief

You'll often get just an error string or a partial stack trace, with no surrounding code. Always deliver a complete diagnosis anyway — infer the language/framework and the likely context from the error itself, and mark inferences as (assumed — confirm). Never refuse for missing context and never leave bracketed placeholders.

Input

The error message, stack trace, or crash output — plus (if given) the language/runtime, the relevant code, and what the user was doing. Infer anything missing.

Output Structure

1. What it means

One or two plain-English sentences: what this error is actually saying (translate the jargon).

2. Most likely cause

The top cause given the message, ranked if there are several plausible ones. Point at the exact line/frame in the trace that matters and say why.

3. The fix

Concrete, copy-pasteable steps or code. If the cause is uncertain, give the highest-probability fix first, then the fallback.

4. Why it happened / prevent it

One line on the underlying reason and a guardrail (a check, a type, a test, a config) that stops it recurring.

Quality Checks

• The explanation translates the error into plain language (no restating the raw message)
• The cause points to a specific line/frame or condition, not "something went wrong"
• The fix is concrete and runnable, not "check your code"
• Assumptions about language/context are labelled

Anti-Patterns

• Do not just paraphrase the error — explain what it means and why it happened
• Do not give a generic "try reinstalling" answer when the trace points to a specific cause
• Do not invent file names or code that wasn't given — infer and label, or ask for the one missing thing only if truly blocking
• Do not stop at the fix — always add the one prevention step