How do you compare two versions of a lease with ChatGPT or Claude?
Paste the old lease and the new draft into your assistant, ask for a table with one row per changed clause (old wording, new wording, who the change favors), then check every number and date yourself with Word or Google Docs compare. The assistant is good at spotting a moved or reworded clause. It is not reliable at noticing that 5 became 6, so treat its table as a reading guide, never as the final check.
When a two-version compare helps
You hold two drafts and need to know what is different. Common cases: your old lease against the updated template you plan to use at renewal, a draft you sent against the version a tenant or their lawyer sent back, or a lease from a previous owner against your own form after you buy a building.
A plain compare tool marks every changed character. That is accurate, but a reflowed paragraph or a renumbered section lights up the whole page. An assistant reads for meaning, so it can say "the grace period moved from clause 4 to clause 7 and is unchanged" instead of showing a wall of red.
Prepare both versions first
- Accept or reject all tracked changes in each file so each draft is one clean version. Otherwise the assistant reads edits and original text mixed together.
- Copy the full text of each version into the chat, one after the other, and label them: "VERSION A (current lease)" and "VERSION B (new draft)". Do not paste only the sections you think changed.
- Remove what the task does not need: tenant names, birth dates, ID numbers and bank details. See what to redact before pasting a lease.
- Tell the assistant the state and whether the lease is fixed term or month to month, so it can flag clauses that tend to be state sensitive.
A prompt that returns a usable table
Copy this and fill in the brackets:
- Compare VERSION A and VERSION B of this residential lease for a [state] rental. Return a table with the columns: clause topic, wording in A, wording in B, what changed in plain words, and who the change favors (landlord, tenant or neither).
- Include every difference in money, dates, time periods, notice requirements, fees, rights of entry, renewal terms and who pays for what, even small ones.
- Then list anything that is in A but missing from B, and anything in B that is not in A.
- Quote the exact words from each version. Do not paraphrase numbers. If you are unsure whether two clauses mean the same thing, say so.
The last line matters. Asking for exact quotes lets you search for the words in your own file and see the assistant did not invent a clause.
Verify the table in ten minutes
Two checks catch most mistakes.
- Run a real compare. In Word, open the Review tab and choose Compare. In Google Docs, use Tools, then Compare documents. Any changed number or date the assistant missed will show up here.
- Search both files for the quoted wording of five high-stakes items: rent amount, due date and grace period, late fee, deposit amount, and notice to end the tenancy. Confirm each quote exists exactly as shown.
Example a made-up current lease says rent is $1,450, due on the 1st, late after the 5th, with a $60 late fee. The new draft says $1,495, due on the 1st, late after the 3rd, with a 5% late fee. The assistant's table should show three changes. Five percent of $1,495 is $74.75, so the late fee in the new draft is higher than $60 by $14.75, and the grace period is two days shorter. A reader who only skims the summary might miss that two of the three changes favor the landlord, and your state may cap or limit both.
What the assistant cannot do for you
- It does not know whether a clause is legal in your state. A change it calls neutral can still run into a state cap on late fees or a required notice period. Check the statute for your state.
- It can miss a one-character change, such as a date or a dollar figure, especially in a long document. That is why the real compare comes first.
- It cannot see attachments you did not paste: addenda, a move-in checklist, a pet policy or house rules. Compare those the same way, one document at a time.
The NIST AI Risk Management Framework describes the same habit in general terms: decide what a human must check before relying on a model's output. For a lease, that check is the number-and-date pass above.
How DoorKeeping handles it
With your assistant connected to DoorKeeping, you can ask for a lease and every document attached to it, with who signed and when, so you start from the version that was actually signed instead of a file on a laptop. You can also ask the assistant to draft a renewal offer from the lease terms, and it lands in your approvals queue for you to review before anything is sent. Rent stays in your own bank account, and anything involving money waits for your approval. DoorKeeping gives no legal advice: have your own attorney read a lease before you rely on a changed clause.
Sources
- NIST: AI Risk Management Framework, read Oct 30, 2026
- IRS Publication 527: Residential Rental Property, read Oct 30, 2026
- DoorKeeping: Connect Claude or ChatGPT (steps and tools list), read Oct 30, 2026
Questions
- Can ChatGPT compare two PDFs of a lease?
- It can if it can read the text. Scanned pages with no text layer often come out garbled, so copy text from the original file when you can, or run the PDF through text recognition first and check the result.
- Is the AI comparison as accurate as Word compare?
- No. Word and Google Docs compare mark every character change. The assistant explains meaning but can miss a changed digit, so use both: the tool for accuracy and the assistant for understanding.
- Should I paste the tenant name into the chat?
- Usually not. The comparison does not need names, birth dates or bank details. Replace them with placeholders such as TENANT before pasting.
- Can the assistant tell me if the new lease is legal?
- It can point to clauses worth checking, but it cannot give a dependable legal answer for your state. Check the statute, or ask an attorney, before using a changed clause.