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Explain a Function's Contract, Invariants and Side Effects
Prompt
Code (the function plus anything it calls that I could find): {{CODE}}
Where it is called from, if known: {{CALL_SITES}}
Explain it in this order:
1. Purpose in one sentence, in business terms if you can tell them.
2. The contract: inputs and their assumed types and ranges, return value, and every way it can fail (exceptions, error returns, null or empty results).
3. Invariants: what must be true before and after it runs. Point to the exact lines that rely on each one.
4. Side effects: I/O, mutation of arguments or shared state, logging, caching, time or randomness.
5. A walk-through of the non-obvious lines only (quote each line, then explain it). Skip the boilerplate.
6. Traps for the person changing it: hidden coupling, ordering dependencies, performance cliffs, and behavior that looks like a bug but might be deliberate.
Cite line numbers or quoted code for every claim. If you can't tell something from the code shown, write "Not visible in the snippet" instead of guessing.
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About this prompt
“Explain a Function's Contract, Invariants and Side Effects” is a free prompt for ChatGPT in the Coding & Software category, 188 words long, added to The Prompt Index on October 28, 2026 by The Prompt Index. Copy it with the button above, paste it into ChatGPT or any other AI chat assistant, and send it.
It has 3 placeholders to fill in first:
{{LANGUAGE}}, {{CODE}}, {{CALL_SITES}}.
Use the “Customize this prompt” fields to personalise it before you copy.
Recommended models: ChatGPT, Claude, Gemini.
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