You read the whole redline twice and still missed the change. Ten minutes teaching AI to compare two versions of a document saves you a full reread every time something comes back revised, and it catches the change you would have skimmed past.
| Core prompt structure | Old text, then new text, then “list only what changed” |
|---|---|
| Change categories | Added, Removed, Changed |
| Prompt placement rule | Source documents before instructions improves recall |
| Governing standard | ABA Model Rule 1.1 duty to review AI output |
1. Name your repeat comparison job
Pick the document type you get in two versions often. It could be a revised offer letter, a vendor contract redline, an updated policy, or a job description that changed after you applied. This is the job you will hand to AI from now on.
2. Paste old and new, ask for only the differences
In one prompt, paste the old text, then the new text, then ask: Compare these two versions. List only what changed, grouped as Added, Removed, Changed. Ignore spelling and formatting differences. Do not ask it to summarise the whole document, only the difference.
3. Ask it to flag what matters, not just what moved
Add one line: For each change, say whether it affects money, dates, obligations or scope, and flag those first. This turns a list of edits into a list of things worth your attention.
4. Read the flags before you read the file
Two minutes over AI’s list tells you if anything needs a proper look. Nothing material, you skip the document entirely. Something material, you go straight to that clause instead of hunting for it.
5. Save the exact wording as a note
Keep the prompt phrasing in your notes app so you can paste it in fresh next time a document comes back revised. No rebuilding it from memory under time pressure.
A worked example
A recruiter emails a second version of your offer letter three days after the first.
Before
OLD: Base salary AED 18,000/month. Notice period 30 days. Probation 6 months.
NEW: Base salary AED 17,500/month. Notice period 60 days. Probation 6 months. Signing bonus AED 5,000, clawback if you leave within 12 months.
Compare these two versions. List only what changed, grouped as Added, Removed, Changed. Flag anything affecting money, dates, obligations or scope first.
After
Changed (flagged, affects money): Base salary reduced from AED 18,000 to AED 17,500 per month.
Changed (flagged, affects obligations): Notice period doubled from 30 to 60 days.
Added (flagged, affects money and obligations): Signing bonus of AED 5,000 with a 12 month clawback if you resign early.
Unchanged: Probation period stays at 6 months.
Three ways to bend it
For a manager reviewing policy updates
Paste the old HR policy and the redlined new version. Ask AI to list only substantive changes and who is affected, and to skip wording tweaks that don’t change meaning.
For a founder reviewing vendor contracts
Paste the old and new SOW or agreement. Ask AI to flag changes to price, term length, liability and termination clauses before anyone signs.
For a job seeker comparing JD versions
If a job posting gets edited after you apply, paste the old and new text and ask what requirements or responsibilities were added, so you know whether you still fit.
When it goes wrong
AI keeps pointing out spelling and formatting changes I don’t care about.
Add one line to your prompt: ignore spelling, punctuation and formatting only changes. Save that version so you never have to retype it.
It missed a change I later found myself.
Long documents get better results split into sections. Paste one section at a time instead of the whole document in one go.
The two versions aren’t in the same format, one is a PDF and one is an email.
Copy both into plain text first. Mismatched formatting confuses the comparison more than the actual wording does.
When not to use this
This is for catching what changed, not for deciding what a contract or policy means. If the document is legally binding and the flagged change is significant, such as pay, notice period or liability, use AI to find it fast, then get the right person, a lawyer, HR, whoever owns that document, to confirm before you act on it.
What you can now do
You stop rereading whole documents from the top and start reading only what actually moved.
Part of Making Life Easier With AI, a weekly walk-through of one small thing AI can take off your plate.
Take this further
Act as a blunt hiring manager who has read ten thousand resumes, not a career coach. I will paste my full resume and the job description I want. Rewrite the whole resume for that role, section by section, in this order: summary, experience, skills, education. Rules: every experience line leads with impact, not duty. Use bracketed placeholders like [8 percent] for any number I did not give you, and list at the end every placeholder I need to replace with a real figure. Keep it to one page of text. Plain formatting only, no tables or columns, so screening software can parse it. After the rewrite, tell me the three weakest claims that need evidence before I send this anywhere. My resume: [paste resume]. The role: [paste job description].
Takeaways
- Write down the exact comparison prompt in a notes app now, before the next revised document lands, so you paste instead of retype under time pressure.
- Add the line ignoring spelling, punctuation and formatting changes to your saved prompt so the output only shows substantive edits.
- For any document over a few pages, split it into sections and compare one section at a time instead of pasting the whole thing at once.
- Convert PDFs and emails to plain text before pasting them in when the old and new versions come in different formats.
- Route any AI-flagged change involving money, dates, obligations or scope to the person who owns that document before you sign or respond.
Questions people actually ask
How do I get AI to only show me what changed between two documents instead of a full summary?
Paste the old text, then the new text, in one prompt, and explicitly ask it to list only what changed, grouped as Added, Removed, and Changed, while ignoring spelling and formatting differences. Anthropic’s own guidance on long documents confirms putting the source text before your instructions improves recall accuracy on comparison tasks.
Can I trust AI to catch every important change in a contract or offer letter?
No. Treat it as a fast first pass, not a final check. Legal guidance on AI contract review consistently says AI should surface deviations and flag issues while a qualified person still reviews anything material, such as pay, notice periods, or liability, before you sign or act on it.
Why does AI keep flagging spelling and formatting changes I don’t care about?
By default AI treats every difference as equal. Add one explicit line to your prompt telling it to ignore spelling, punctuation, and formatting only changes, and save that exact wording so you never have to retype it under time pressure next time a document comes back revised.
What should I do if the old and new document are in different formats, like a PDF and an email?
Convert both to plain text before pasting them in. Mismatched formatting, like tables in a PDF versus plain paragraphs in an email, can confuse the comparison more than the actual wording does, increasing the odds AI misses or misreports a real change.
Is it safe to rely on AI’s comparison for a legally binding document?
Use it to find changes fast, not to decide what they mean. If the document is legally binding and a flagged change is significant, bar guidance under ABA Model Rule 1.1 puts the duty on the professional to review AI output, not skip it, so route it to a lawyer, HR, or whoever owns the document before you act.
Sources
What happens next
Expect more document tools to build this compare-and-flag pattern in natively, rather than leaving it to a manual prompt, as vendors in contract and HR software race to add redline assistants. Watch whether those built-in tools disclose their limitations as clearly as the manual prompt does, since a tool that hides its blind spots is riskier than one you’re actively steering yourself.
