Browser ↔ local daemon communication — without WebSocket code.

SDK for local-first tools. Reconnects, multiplexing, NAT traversal built in.

• sideband — SDK and protocol

You built a local daemon with a browser UI. It works on your machine.

Then real users arrive:

• WebSocket reconnects break on flaky networks
• NAT and firewalls block connections
• Tabs desync, messages get lost
• Support tickets pile up for issues you can't reproduce

You didn't sign up to become a networking expert.

• Works behind NAT and firewalls
• Automatic reconnects and multiplexing
• End-to-end encrypted (relay can't see your data)
• TypeScript-first (Node, Bun, browser)

You ship your product. Sideband handles the hard parts.

• Indie devs building local AI agents or dev tools
• Anyone maintaining a flaky custom WebSocket layer
• Tools that outgrew "localhost-only"

• Open protocol, documented in the open
• Relay is replaceable and self-hostable
• Security built-in, not bolted on

Actively developed. Protocol design is stable; SDK APIs may evolve.

Feedback welcome — especially from teams building local-first tools.