add-ssh-key

name	add-ssh-key
description	Add an SSH public key to a remote server's authorized_keys file
argument-hint	<public-key> <user@host>
allowed-tools	["Bash","Read"]

Add SSH Key to Remote Server

Add an SSH public key to a remote server so a user can authenticate via SSH.

Input

Parse $ARGUMENTS for:

1. Public key — a string starting with ssh-rsa, ssh-ed25519, ecdsa-sha2-*, or sk-*
2. Target server — in user@host format (e.g., root@134.122.74.255)

If either is missing, ask the user to provide it.

Validation

Validate the public key format

• Must start with a recognized key type (ssh-rsa, ssh-ed25519, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521, [e-mail], [e-mail])
• Must be a single line (no embedded newlines)
• Must have at least 2 space-separated parts (type + base64 data), optional comment

If invalid, show what was received and ask the user to double-check.

Verify SSH access to the target server

ssh -o ConnectTimeout=5 -o BatchMode=yes <user@host> "echo ok"

If this fails, inform the user they don't have access to the server and cannot proceed.

Check for Duplicates

Before adding, check if the key already exists:

ssh <user@host> "grep -F '<base64-portion-of-key>' ~/.ssh/authorized_keys 2>/dev/null"

Extract the base64 portion (second field) for matching. If the key is already present, tell the user and stop — do not add it again.

Preview and Confirm

Show the user a summary before making changes:

SSH KEY ADDITION

Server:  <user@host>
Key:     <key-type> <first 30 chars of base64>...<last 10 chars> <comment>
Comment: <comment from key>

Proceed? (yes / cancel)

Add the Key

After user confirms, append the key to the existing authorized_keys file:

ssh <user@host> "echo '<full-public-key>' >> ~/.ssh/authorized_keys"

Do NOT create directories or change permissions — assume ~/.ssh/authorized_keys already exists with correct permissions.

Verify

After adding, confirm the key is present:

ssh <user@host> "tail -1 ~/.ssh/authorized_keys"

Report success and remind the user to have the key owner test access:

Key added successfully. Ask them to test with: ssh <user@host>