Add an SSH Key to GitHub (Mac, Windows, Linux)

SSH lets you push and pull without typing a token every time. It takes about five minutes.

On Windows, run these commands in Git Bash (installed with Git for Windows) or PowerShell. The commands are the same unless noted.

Step 1: Check for an existing key

ls -al ~/.ssh

If you see id_ed25519 and id_ed25519.pub, you already have a key. Skip to Step 3.

Step 2: Generate a new key

ssh-keygen -t ed25519 -C "you@example.com"

• Press Enter to accept the default location (~/.ssh/id_ed25519).
• Set a passphrase. It protects the key if your laptop is stolen, and the agent means you only type it once.

This creates two files:

Step 3: Add the key to the SSH agent

macOS:

eval "$(ssh-agent -s)"

Create or edit ~/.ssh/config:

Host github.com
  AddKeysToAgent yes
  UseKeychain yes
  IdentityFile ~/.ssh/id_ed25519

Then:

ssh-add --apple-use-keychain ~/.ssh/id_ed25519

Keychain now remembers the passphrase across restarts.

Linux:

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519

Windows (PowerShell as admin, once):

Get-Service ssh-agent | Set-Service -StartupType Automatic
Start-Service ssh-agent
ssh-add $env:USERPROFILE\.ssh\id_ed25519

Step 4: Copy the public key

pbcopy < ~/.ssh/id_ed25519.pub              # macOS
cat ~/.ssh/id_ed25519.pub                   # Linux: copy the output
Get-Content ~/.ssh/id_ed25519.pub | Set-Clipboard   # Windows PowerShell

It's one line starting with ssh-ed25519.

Step 5: Add it to GitHub

1. GitHub → your avatar → Settings → SSH and GPG keys.
2. New SSH key.
3. Title: something that names the machine ("MacBook 2026").
4. Key type: Authentication Key.
5. Paste, save.

Step 6: Test

ssh -T git@github.com

The first time, type yes to trust GitHub's host key. You should see:

Hi your-username! You've successfully authenticated, but GitHub does not provide shell access.

Step 7: Use SSH remotes

Clone with the SSH URL (git@github.com:user/repo.git), or switch an existing repo from HTTPS:

git remote -v
git remote set-url origin git@github.com:your-username/your-repo.git

Fixing "Permission denied (publickey)"

Run the test verbosely to see which keys are being offered:

ssh -vT git@github.com

Then check these in order:

1. Is the key loaded? ssh-add -l. If it says "no identities", run ssh-add again.
2. Did you paste the .pub file into GitHub, and into the right account?
3. Is the remote SSH? git remote -v should show git@github.com:..., not https://.
4. Permissions. SSH ignores keys other users can read:

chmod 700 ~/.ssh
chmod 600 ~/.ssh/id_ed25519
chmod 644 ~/.ssh/id_ed25519.pub

See chmod 755 vs 644 for what those numbers mean.

5. Port 22 blocked on office or campus Wi-Fi? GitHub accepts SSH on port 443:

Host github.com
  Hostname ssh.github.com
  Port 443
  User git

Two GitHub accounts on one machine

Make a second key and give each account a host alias in ~/.ssh/config:

Host github-work
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_ed25519_work
  IdentitiesOnly yes

Then clone work repos with the alias:

git clone git@github-work:company/repo.git

Bonus: sign commits with the same key

git config --global gpg.format ssh
git config --global user.signingkey ~/.ssh/id_ed25519.pub
git config --global commit.gpgsign true

Add the same public key in GitHub again, this time as a Signing Key, and your commits show as "Verified."

Related

• Git & GitHub From Zero to Collaborating Like a Pro
• Git vs GitHub
• chmod 755 vs 644