tailSync | Devpost

ui frontend

Inspiration

Hackathons move fast. You’re constantly sending files, screenshots, and quick context updates while coding in parallel. The usual “fast” collaboration tools under time pressure come with tradeoffs:

public-by-default links
accounts and permission setup
port forwarding / exposing local services
too much overhead for a weekend

We wanted something smaller and sharper: a tiny workspace for two devices—chat + file drops + “send this screenshot right now”—but private by design.

When we saw the Tailscale challenge prompt, we realized the cleanest solution wasn’t to bolt security onto collaboration—it was to make collaboration a tailnet-only service where ACLs are the security boundary.

That’s why we built tailSync: a secure mini-workspace built on your tailnet.

What it does

tailSync creates a shared workspace between exactly two devices on a Tailscale tailnet.

Core features

1) Realtime chat

Instant messaging between host and joiner
Timestamps + sender identity

2) File sharing

Upload any file to the host workspace
The other device instantly sees it in the feed and can download it

3) Screenshot → shared feed

One-click screenshot capture (with optional caption)
Posted as an image card in the workspace feed, in real time

4) Connection panel

Shows Host/Join status, workspace code, and connection details
Clear error if blocked: “Blocked by Tailscale ACL or not on tailnet.” tailSync does not rely on a public backend. The workspace is a private service:
Host service runs locally
Published to a tailnet HTTPS URL via Tailscale Serve
Join happens only via HTTPS/WSS over the tailnet
ACLs determine whether the joiner is allowed

Challenges we ran into...

1) Making Tailscale truly essential We avoided the common hackathon path (public server + “also Tailscale”). Instead:

host service stays localhost-only
Serve URL is the only join path
ACLs control access, not app-level auth

2) Clear UX when ACL blocks An ACL denial can look like a network timeout. We built explicit error messaging so the demo is understandable:

“Blocked by Tailscale ACL or not on tailnet.”

3) Realtime correctness We kept the realtime protocol simple:

WebSocket broadcasts for chat, post:new, presence
HTTP endpoints for file upload/download and feed refresh

Accomplishments that we're proud of

Tailscale demo: tailnet + ACL enforcement + Serve URL required
Instant collaboration loop: screenshot → upload → appears on other device in realtime
No external backend: the workspace is private and self-hosted
Clear architecture + demo story: judges can see exactly why Tailscale matters

What's next for tailSync

Add Tailscale identity-aware join (auto label users using tailnet identity)
Add role-based permissions derived from tailnet groups (host/admin vs viewer)
Add a persistent side panel mode and keyboard shortcuts
Add lightweight encryption at rest for uploaded files

Built with

Client: Electron + React (Vite), TailwindCSS, OS Snipping integration, notch toolbar overlay
Backend: Node.js, TypeScript, Express, ws, multer
Infra: Tailscale Serve (required), Tailscale ACLs (required) for access control