Which tool to choose
For comparing pasted texts any AI assistant is fine: reading and comparing is its terrain. If the two texts are whole documents (two versions of a twenty-page contract), an assistant you can attach the files to instead of pasting them in pieces is preferable. For purely mechanical comparisons between text files there are also dedicated tools that show the differences line by line; but the AI has an advantage: besides telling you what changed, it tells you whether the change matters.
How to do it
Comparing two texts by eye is where fatigue does the most damage: the small differences — a date, a figure, an added "not" — are the easiest to miss and the most costly. The AI catches them all, if you ask in the right way.
- Label the two texts clearly: "VERSION A" and "VERSION B," with a clear boundary between them.
- Ask only for the differences, not a summary of both: "list what changes from A to B."
- Ask for the before/after format: for each change, the sentence as it was and as it became.
- Specify what to focus on if you're interested in one aspect: only the numbers, only the clauses, only the tone.
- If needed, ask for a judgment separately: "which of these changes improve the text and which make it worse."
The operational syntax:
Compare the two versions below and list only the differences. For each change write the sentence as it was in A and as it became in B. Flag in particular every change of numbers, dates, amounts or negations. Don't summarize the texts, give me only what changed.
VERSION A:
"""
[text A]
"""
VERSION B:
"""
[text B]
"""
After the list, if the texts really matter (a contract, a quote), reread yourself the flagged points in the original versions: the AI showed you where to look, but you put the signature on the documents that commit you.
A concrete example
Marco receives the new version of a contract with the supplier, "just a few small changes" he's told. Instead of rereading twenty pages, he pastes the two versions and asks it to list every difference, with special attention to amounts and deadlines. The AI finds four changes: three marginal and one not, the payment terms moved from sixty to thirty days. That "small change" would have changed his liquidity. He notes it, he renegotiates it. Without the pointed comparison it would have slipped by unnoticed.
When it does NOT work (and how to fix it)
If the AI summarizes the two texts instead of comparing them
You asked "compare" without specifying the output. Be explicit: "don't summarize, list only the differences in before/after format." The verb "compare" alone is ambiguous; "list what changes from A to B" isn't.
If you have the doubt that it missed some difference
On long texts it can happen that it omits one. Narrow the field to be sure on the critical points: "check line by line all the numbers and dates, tell me which ones differ." A targeted pass on the sensitive data is more reliable than a general overview, and for what matters you can always reread the flagged points yourself.
If the two texts are too long to paste together
Attach them as files if the assistant allows it, or compare one section at a time: "let's compare only chapter 3 of both versions." Breaking the comparison into blocks maintains the precision that two very long texts pasted in their entirety would lose.
A tip from someone who actually uses it
Always ask the AI to highlight the changes to numbers, dates and negations, even when you expect only style changes. These are exactly the differences that change the substance while staying invisible to the eye: an added "not" flips a clause, a figure shifted by a decimal point changes everything. The difference that does damage is almost always small and silent.
Frequently asked questions
Can I compare files too and not just pasted text?
Yes, if the assistant allows attaching documents. It's actually the best way for long texts, because you avoid the box's limits and the AI reads the whole versions. Label clearly anyway which file is the old version and which the new.
Does the AI really find all the differences?
On the obvious changes it's very reliable; on long texts a minimal difference can escape it. That's why, on documents that commit you, use a targeted pass ("check all the numbers and dates") and reread the flagged points yourself. The AI saves you the full reading, not the responsibility of the signature.
Isn't a program that compares texts automatically safer?
For the mechanical line-by-line comparison, those programs are precise and work just fine. But they tell you what changed, not whether it matters: they show you that a word is different, without flagging that that word shifts a deadline. The AI adds exactly the judgment on the weight of the change, which is often what you really need in order to decide what to do.