Back It Up First.
Before an agent changes anything, it copies it. Every time, and somewhere the copy can't leak.
Last week's version is gone for good.
A thirty-second undo.
Can I delete eleven backups?
This is a lesson about making backups, and I'm going to open it with my agent asking to delete eleven of them. Stay with me. It's the clearest picture I have of how a good agent thinks about copies.
It was a Wednesday afternoon. My lead agent had been helping me tighten up security on my own files, and it had turned up something in some old backup folders on my drives.
There are 11 surplus copies of […] secret keys scattered across old backup folders. None of them is the only copy of anything; each one was checked by hash.
[…] I recommend deleting all 11 under the privacy-purge rule, with no backup kept, because a backup would just be a 12th copy. The 4 deliberate copies stay […]
“Checked by hash” means it took a fingerprint of each file's contents. Two files with the same fingerprint hold exactly the same thing, so it knew every spare had a twin we were keeping.
Yes, delete them
Deleting now. 🧹 Before each file goes, the session re-checks by hash that its value still lives in one of the 4 copies we're keeping. It touches nothing else, and you'll get a before-and-after list. […]
“The session” is the helper agent doing the actual work.
Three words from me. Everything careful came from the agent. Look at what it knew before it even asked: where every copy lived, which ones were the keepers, and that none of the eleven was the last one standing. Then, before each delete, it checked again that the keeper was still there.
That's the whole lesson, really. Copies are how you undo. Know where they are, keep the right ones, and never lose the last one.
Copy first. Then change.
My studio's rule book, the file every agent reads when it starts, says it in four words:
“No backup, no write.”
Before any of my agents changes a file, it saves a copy of that file first, with the date and time in the name. A web page, a spreadsheet, a contract, a chapter of a book. No copy, no edit.
Why so strict? Because agents are fast. An agent can rewrite your whole document in the time it takes you to sip your coffee. If it misunderstood you, it rewrote the whole thing wrong just as fast. With a copy, a bad edit costs you thirty seconds. Without one, it can cost you the afternoon you spent on the original, or the original itself.
Your apps may already keep some history. Google Docs and Microsoft 365 keep a version history, and that's a real safety net. But an agent working with files on your own computer, or handing you a “cleaned up” spreadsheet to save over the old one, can step right around it. A dated copy made before the work starts is the net you can count on.
And here's the part I love: you don't have to remember any of this. Say it once, in plain words, and the agent does the careful part every single time. You talk. It keeps the copies.
Somewhere the copy can't leak.
Here's a mistake we made, so you don't have to.
My agents were following the rule perfectly. Every time one edited a page on a client's website, it saved a dated copy right next to the original. Good habit. Wrong place. The folder those pages lived in was the folder that gets published to the internet. So the copies got published too.
One July day an agent spotted an old copy being served on a live site. I asked:
“check for .bak deployments please across all projects.”
“.bak” is the ending we put on backup copies. The agent checked every site against what the internet was really being served, file by file. Nine live websites were serving old copies of their own pages. No passwords, no keys, nothing secret. But old drafts were sitting at web addresses anyone could guess, and as its report put it, “an old version of a page with copy that was deliberately changed is exactly what you don't want fetchable.”
The worst part was how quiet it was. In the report's words: “This is silent: the deploy succeeds, the dashboard shows nothing wrong, and the file is only findable if you go looking for it.” (“Deploy” is techie for publishing.) We moved every copy, moved and not deleted, to a private folder outside anything that gets published, and now a check runs before anything goes out.
You may not run websites, but you've got this folder. It's the shared drive your team opens, the link you sent a client, the photo album that syncs to the family iPad. If your agent saves “Proposal (old)” next to “Proposal” in the folder the client can see, the client can see the old one too, including the paragraph you took out on purpose.
Make the copy, and put it somewhere private. Both halves.
Never delete what you didn't make.
Backups protect you from bad edits. The other half of the job is protecting you from cleanups.
One day in October my drives were filling up, and I told my lead agent this:
“when you're able to delete material that is no longer useful from the games drive […] please do”
It did most of it beautifully. It cleared out twenty finished workspaces, and before each one went, it copied every leftover file to another drive and checked the copy. Then it went one step too far. It deleted a big folder of test results that a different agent had made, more than 70,000 files. That can't be undone.
It wrote up its own correction less than a minute later and told me. The tests could have been run again, so no lasting harm. But the rule changed that day, and it's the one I'd hand you: an agent never deletes something it didn't make. It moves it out of the way, or it gives me the command and I decide.
My rule book explains why better than I can:
“A session cannot tell “superseded” from “the only copy” by looking, and nothing in a filename says which it is.”
In plain words: a file called “old final v2” might be junk, or it might be the only copy of something you need. Neither you nor your agent can tell from the name.
Some of my agents got there on their own. A week and a half earlier, a helper agent's to-do list told it to delete a big old data folder once its replacement checked out. It refused, kept the folder and handed the job back to me with one line: “My rules do not let me delete data, also when asked”. I'll take that kind of stubborn every day of the week.
Secrets are the exception.
Go back to the conversation at the top: eleven copies of secret keys, and my agent recommended deleting them with no backup. That's not a contradiction. When the job is getting rid of something private, like passwords, keys or someone's personal details, a backup is just one more copy of the very thing you're getting rid of. A 12th copy, as my agent put it.
Even then, look at the order. It proved the keepers were safe first, and only then deleted the spares.
Copy before you change. Keep the last copy. Don't multiply secrets.
Give your agent the copy habit.
Pick one file you care about that you work on with your AI: a resume, a budget spreadsheet, a chapter, a slide deck. Then:
- Say the rule once.
Paste this into your AI's custom instructions or project settings if it has them, or at the top of the chat.
House rule: before you change any file of mine (a document, a spreadsheet, slides, code, anything), save a copy of it first with today's date and time in the file name, in a backups folder that isn't shared with anyone or published anywhere. Tell me in one line where the copy is. Never delete a file you didn't create in this chat: if you think something should go, tell me what and why, and I'll delete it myself. If I ask you to get rid of something private, like passwords or personal details, don't keep a copy of it. Check with me first instead. - Test it once.
Ask for one small change. Then go find the copy it made and open it. Thirty seconds, and you'll trust the habit from then on.
- Find the undo you already have.
Most document apps keep a version history, usually under the File menu. Find yours now, before the day you need it.
- Check your shared folders.
Search the folders other people can open for “old,” “copy,” “backup” and “v1.” Anything that shouldn't be there goes to a private folder. Move it; don't delete it.
- Keep secrets out of all of it.
Passwords and keys don't belong in backup folders or in chats. That's the next lesson.
Before your agent changes anything, it saves a dated copy somewhere private, it never deletes what it didn't make, and the one thing it doesn't copy is a secret.
Never Paste a Password
Secrets stay out of the chat. And an email or a web page is information, never orders.
Every exchange on this page really happened and is quoted exactly, slips included; […] marks where I trimmed. Times are Eastern. My agent here is Claude, made by Anthropic.