I Compared 5 Prompts for Summarizing Long Documents

Summarization is the single most common reason people use AI, yet comparisons of "how to ask for a good summary" are surprisingly rare. So I took one 30-page public industry-trends report and had it summarized five times, changing only the prompt.

Method

• Same document, same AI, fresh chat every time (to remove carryover from earlier turns)
• Scoring criteria: ① missing key points ② content not in the original (hallucination) ③ how usable it is as-is
• I read the original closely first and fixed a list of "7 must-include key points" before grading

The 5 prompts and how they did

① "Summarize this" (4 out of 7)

It did the basics but skewed heavily toward the front of the document. Only 4 of the 7 key points made it in. The important counterargument section near the end was dropped entirely.

② "Summarize this in 3 lines" (3 points)

Short meant clear, but also mushy. A sentence carrying zero information — "several challenges remain" — took up one of the three lines.

③ "Summarize as: core claims / evidence / limitations" (6 points)

Specifying a structure made quality jump. Giving it a dedicated "limitations" slot brought back the counterargument section that ① had dropped.

④ "A summary to report to my manager, focused on what's needed for decisions" (6 points)

Naming the audience made the sentences practical. It even added interpretation — "this is an opportunity for us because…" — which is both a strength and something to watch (the interpretation can be wrong).

⑤ ③+④ combined, plus "add nothing that isn't in the original; cite the source page for each item" (7 points)

The winner. All 7 key points included, and the page citations made verification fast. Zero hallucinated sentences.

What I learned

• Summary quality depends less on "how smart the AI is" and more on "how you ask."
• Structure (③) + audience (④) + citations (⑤) are the holy trinity. In particular, "add nothing not in the original" and "cite the page" cut verification time dramatically.
• Use "3-line summary" only to jog your memory on a document you already know. On a document you've never read, it's risky.

Final recommended prompt: "Summarize this document using the structure [core claims / evidence / limitations & counterarguments]. Focus on what I need for decisions in [my situation]. Add nothing that isn't in the original, and cite the page where each item appears."