Check an AI summary against the original
A summary is only useful if you can trust it without rereading the whole document. Paste the original and the summary to see where each sentence comes from and which figures and names are not in the original. It also lists what the summary left out. Nothing you paste leaves this browser.
No original to check against? The Fact Check List lists every claim worth looking up.
New to this? What it does, in plain words
It lines up an AI summary with the document it came from, and shows which parts of the summary the document does not back up.
Use it before a summary goes to someone who will act on it: meeting notes for people who were not there, a report boiled down for a director, a contract or a long thread condensed for a client, a chapter summarized for revision. It is built for the moment when you have not read the whole original yourself.
What you need
The original text and the summary. No API key and no sign-up. Both are read in this browser and sent nowhere.
How to use it
- Paste the original on the left and the summary on the right. The check runs as you paste.
- Start with the sentences marked No match in the original, then the details marked as not in it.
- Look through what was left out, and press Add it on anything the summary needs.
- Copy the prompt, or open it in your AI, to have the summary corrected from the original alone.
The original
ExampleThe AI’s summary
Both texts stay on this device. The check is done by rules in this page, with no AI and no upload.
Paste the original and its summary. Each sentence of the summary is traced back, and its numbers, dates, names and quotes are looked for in the original.
The summary, sentence by sentence
Each one with the sentence in the original that says it.
Left out of the summary
Ask the AI to fix the summary
Names each point still marked, and asks for a summary that uses only what the original says.
Where to next
Where AI summaries go wrong
A summary reads as confident whether or not the document supports it. The errors are small and specific, which is why they survive a quick read.
- In your browser. Paste both textsThe original, and the summary of it.
- In your browser. Sentences are tracedEach summary sentence is matched to the place in the original that says it.Instant
- In your browser. Details are checkedNumbers, dates, names and quotes in the summary are looked for in the original.
- In the AI you use. Have it correctedOne prompt that fixes the marked points from the original alone.
What it looks for
- Sentences with no match. A line in the summary that no part of the original says. It may be a fair conclusion, or it may be invented.
- Details that are not in the original. A figure or a name that appears in the summary and nowhere in the source.
- Figures the AI worked out. A total or a difference, such as “grew by 16” where the original says “from 212 to 228”. The sum is shown so you can check it.
- Rounded figures. “About $4.2 million” for $4,236,000 is marked as rounded, not as wrong.
- Quotes. Words in quotation marks have to appear in the original exactly.
- Caution that went missing. The original says “may” or “preliminary”, and the line that sums it up states it as settled.
- What was left out. The amounts, dates, names and quotes the original gives and the summary does not, starting with the ones the original repeats.
“On-time delivery was about 94%, short of the 95% target.”
Not quite. 93.6% rounded to 94% and said to be “about”. A fair summary.
“On-time delivery missed its 95% target after three carrier failures.”
Yes. The report says two failures. A changed count is easy to miss because the sentence still sounds right. Summary Check marks “three” as not in the original.
“Delivery fell short of target in September.”
Not quite. Vague, and nothing in it contradicts the report.
“Two carrier failures kept on-time delivery under 95%.”
Not quite. Every detail here is in the report.
The dangerous errors are the ones that keep the shape of the sentence and change one detail.
What it cannot do
It matches words and details, and it does not understand either text. A sentence marked as matched can still tilt the original’s meaning, and a sentence with no match can be a sound conclusion drawn from several parts. It cannot tell you whether the summary kept what matters most, because that depends on who is reading. Use it to decide where to read the original, then read those parts.
Questions
How do I check if a ChatGPT summary is accurate?
Compare its details with the original first, because that is where summaries fail: a number changed, or a claim the document never makes. Paste both texts here and each summary sentence is shown beside the sentence it came from, with anything unsupported marked. Then read the marked parts of the original yourself.
Does my document go anywhere?
No. Both texts are read in this browser and nothing you paste is sent to thinkhard.si or anyone else. They are kept in this browser so they survive a reload, and Clear both removes them. If the document names real people or clients, Safe Paste can swap those details for placeholders before you give it to an AI at all.
Why is a sentence marked “No match” when it seems right?
Because the summary used different words from the original, or drew a conclusion the original only implies. The mark means “read this part of the original”, not “this is false”. Press This is fine and it leaves the count and the correction prompt.
Can it check a summary of a PDF or a meeting?
It checks text against text. Copy the text out of the PDF, or paste the meeting transcript, and it works the same way. For a meeting, the transcript is the original, so mishearings in the transcript carry through.
How long can the original be?
Long reports are fine: tens of thousands of words work in a modern browser. Very long texts take a second or two to trace.
How do I get a better summary in the first place?
Say who the summary is for and what they will decide. Ask for every figure to be copied exactly, and for anything the AI was unsure about to be marked. The executive summary prompt does this, and the guide to summarizing long documents with AI explains why.