Can you paste an API key or client data into Claude Code? Where secrets go instead

How to use the secrets table

Claude should know a secret's name, never its value. The table is that one idea, sorted by the kind of secret.

The left column is the thing. The middle column is every place people put it by accident. The right column is the safe home. Keys can be replaced in five minutes. A client's tax ID can't, because there is nothing to revoke. That is why client records get the strictest row.

The deny rules in the table are the lock. The permissions page shows the syntax, and the security page explains the guards Claude Code adds around them.

Know the gaps, too. A read deny rule covers Claude's own file tools and common commands that name a file. It doesn't cover a command that searches a whole folder. Deny rules stop accidents. They are not a vault. The stronger guard is keeping secrets out of the folders Claude works in at all.

The key on your clipboard

The new email tool won't connect. The setup page gave you a long string of letters and numbers and called it an API key. Claude Code is open in the other window.

You copy the key. Your cursor sits in the prompt box.

It's my own computer. What's the harm?

Think of a treehouse password said out loud in class. Everyone heard it. The kid taking notes wrote it down with the date. The only fix is to change the password. A pasted key works the same way. It isn't said once and gone. It gets written down in the session file.

Already pasted a key? Do this today

Most people searching this have already done it. That is fixable. Work in this order, because the first step is the only one that actually closes the leak.

1. Revoke the old key at the service and create a new one.
2. Put the new one in the right place: an environment variable or a git-ignored file. Never back where the old one leaked.
3. Confirm the old key is dead. Try it once, or check the service's key list.
4. Clean up the copies. The pasted key sits in the session transcript under the projects folder in your home .claude folder. The sessions page says you can delete a project's transcripts sooner than the 30-day sweep with claude purge. If you said "remember this" near the key, ask Claude to list its memory notes and remove any line that holds it.
5. Write down the date you did it.

Step 4 is tidying. Steps 1 to 3 are the fix. A deleted copy does not take the key back from anything that already read it.

Check your plan's training setting

The other half of the question is what happens on Anthropic's side. The book's advice is to check this today, not later. On Free, Pro and Max plans, the data-usage page says your data, including Claude Code sessions, is used to train new models when the model-improvement setting is on. Team, Enterprise and API accounts are not used for training unless the customer opts in.

You can see and change the setting at claude.ai/settings/data-privacy-controls. If you handle client records, set it the way your clients would expect, and write down the date you checked. These terms change, so read the current page rather than trusting any summary, this one included.

The secrets I found in my own folders

In September 2026, an audit by my assistant found a real-looking access token in two of my website projects. It wasn't in a .env file. It was in a config file for a code editor's connector, the kind of file nobody thinks of as secret. In one project it had been there since the very first commit.

In July 2026, an audit of another site found a credentials file sitting in the public website folder, and a sign-in secret pasted into a documentation file.

Deleting the file and scrubbing the history feel like the fix. They aren't. Anyone who saw the secret can still use it. A rotation that waits on a to-do list is a leak that is still open.

So I decided once. On July 13, 2026, I wrote one ignore policy for every project instead of choosing project by project. Environment files never go in. Token files never go in. If you hold client records, that folder goes on the list on day one.

The chapters that lock the drawer

This is the problem Claude Code for Non-Programmers was written for. The book is independent and is not affiliated with Anthropic.

Safety and Failure opens with secrets: a search that finds them without printing them, the deny rules, a starter ignore file, a pre-share checklist and a separate checklist for client data. It also covers prompt injection, when a page Claude reads tries to give it orders.

Permissions and Modes explains why a deny rule wins in every mode.

Connecting the World shows how to connect other apps with a sign-in instead of a pasted key.