Tailscale has open-sourced Tailcat, a lightweight networking tool that lets two machines connect directly without either side registering an account or joining the same Tailnet. A machine running Tailcat generates a connection address; sharing that address with another machine enables file transfers, port forwarding, and SSH sessions. The tool builds on Tailscale's WireGuard encryption, NAT traversal, and DERP relay, but removes the need for Tailscale accounts or its control plane. Connections attempt a direct peer-to-peer UDP path after locating each other over DERP, and only fall back to the relay when hole punching fails. The project started as a 2023 prototype by principal engineer Brad Fitzpatrick and was shelved until recently, when AI agents began connecting to sandboxes, remote VMs, and test machines. Fitzpatrick now uses Tailcat to give agents temporary access to Raspberry Pi, EC2, and Windows hosts without pre-provisioning accounts or network setup. Tailcat is not a full Tailscale replacement: it carries no user identity, permission policies, or device management, and connection addresses must be guarded like passwords. Tailscale-hosted DERP relays log metadata and impose rate limits with no uptime SLA; operators needing more stability or privacy can self-host DERP.
Tailscale has open-sourced Tailcat, a networking tool that opens an encrypted tunnel between two machines without either side registering an account or joining the same Tailnet.
Run Tailcat on one machine and it generates a connection address. Pass that address to another machine, and the two can exchange files, forward ports, or open an SSH session.
How Tailcat connects without an account
Tailcat keeps Tailscale's WireGuard encryption, NAT traversal, and DERP relay, but drops the need for a Tailscale account or control plane. The connection flow starts over DERP to locate the peer, then attempts a direct peer-to-peer UDP path. If hole punching fails, traffic falls back to the DERP relay. Everything runs in userspace, so system routing and DNS are left untouched.
A 2023 prototype, revived for AI agents
The project traces back to Tailscale principal engineer Brad Fitzpatrick, who built the Tailcat prototype in 2023 and largely shelved it. With AI agents now hooking up to sandboxes, remote VMs, and test machines in growing numbers, he picked the project back up. He has been using Tailcat to give agents temporary connections to Raspberry Pi, EC2, and Windows hosts, without provisioning accounts and network configs for the agents in advance.
Not a full Tailscale replacement
Tailcat comes with trade-offs. There is no user identity, no permission policy, and no device management, so the connection address itself has to be guarded like a password. Tailscale's hosted Tailcat DERP relay logs metadata, carries rate limits, and offers no uptime SLA. Teams that want more stability or privacy can deploy their own DERP server.
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