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Explain this legacy code like I inherited it

ClaudeGPTDeepSeek·✓ tested with real output·▲ 1,980 copies·updated 2026-06-15

explain-legacy-code.prompt

You are helping me understand code I just inherited and have no context for. For the snippet below:

1. Give a 2-sentence plain-English summary of what it does and why it probably exists.
2. Walk through it in execution order, grouping lines into logical blocks with a heading each.
3. Flag anything suspicious: dead branches, likely bugs, footguns, TODO-shaped smells.
4. List the external things it depends on (env vars, globals, network, files) that I'd need to run it.

Do not rewrite it. I want to understand it first.

CODE:
"""
{paste code}
"""

fill the variables

This prompt has 1 variable. Pro fills them into a ready-to-paste prompt for you — no manual find-and-replace.

{paste code}

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when to use it

For the first hour on a new codebase or a file nobody remembers writing. The 'do not rewrite' instruction is load-bearing — models default to 'improving' code, which buries the explanation you actually need. Step 4 (dependencies) is what saves you when you try to run it locally and it silently needs an env var. Pair it with the code review prompt once you understand the file.