kith — one's own trusted circle. Kith keeps your circle of devices in sync.

Kith is a serverless, end-to-end-encrypted, no-account desktop app for keeping your own devices in sync — your memory/notes, your saved tabs, and your files — directly device to device, with no server that can read them, because there isn't one. Linking a device is a short pairing code, not an account. And because it speaks MCP, your AI assistant can read and add to the very same data.

Built on iroh (QUIC transport, mainline-DHT discovery) and Automerge (CRDTs).

What you get

A single desktop app (Windows · macOS · Linux) with:

• 🧠 Memory — notes and facts that sync across every linked device.
• 🔖 Tabs — save links/pages and have them everywhere.
• 📁 Files — send files straight to your own devices: end-to-end encrypted, no size limit, no cloud, with live progress and a direct-vs-relayed badge.
• 🌐 Spaces — run several independent, end-to-end-encrypted worlds at once: a Personal space for yourself, or a Team space with per-device roles (Admin / Writer / Reader) for a trusted circle. Each space has its own keys, members, and audit log; export any space to an encrypted file for backup or to move it.
• 🔗 Devices — link another computer with a one-time code (SPAKE2). No account.
• 🤖 Agents — point Claude Desktop / Cursor at Kith over MCP; your AI can use your memory, tabs, and files locally — bound to the active space only, so a prompt-injected agent can't reach another space.

Install

Download a build for your OS from the Releases page (Windows .exe, macOS .dmg, Linux .AppImage/.deb/.rpm). Builds are currently unsigned (alpha), so your OS may warn about an unverified developer — on Windows choose More info → Run anyway; on macOS use System Settings → Privacy & Security → Open Anyway.

Or build from source (needs the Rust toolchain + the Tauri prerequisites for your OS):

cargo run -p kith            # build + launch the desktop app
cargo tauri build            # build installers (needs: cargo install tauri-cli)

Connect your AI (MCP)

The same kith binary doubles as a local MCP server. In the app, open Agents to copy a ready-made config, or add this to your MCP client (e.g. Claude Desktop's claude_desktop_config.json) and restart it:

{ "mcpServers": { "kith": { "command": "/path/to/kith", "args": ["serve"] } } }

Your agent then gets memory.*, tabs.*, and files.* tools — operating on the same encrypted replica the app uses, entirely on your machine. With the Kith app open, kith serve automatically bridges to it (one shared engine); with the app closed, it runs standalone.

How it works

• Flat mesh, no hub. Every device is an equal peer holding a full encrypted replica. Changes propagate directly between your devices over iroh QUIC (TLS 1.3).
• CRDT state + gated blobs. Mutable state is an Automerge document (conflict-free, offline-tolerant); files ride content-addressed, BLAKE3-verified blob transfer. Both sync and file transfer are gated by a mutual group-key handshake — a non-member is refused before any byte is exchanged.
• No account. Devices link with a short pairing code (SPAKE2-derived group key); pairing is mutual, so both sides learn each other and converge.
• Spaces, roles & revocation. A device runs N independent encrypted spaces over one connection. A team space roots membership in device identity (EndpointId), not mere possession of the key: a signed, hash-chained membership log, with Admin/Writer/ Reader roles enforced cryptographically against honest peers (a Reader's writes are rejected; a non-member is refused even with a leaked key). Removing a device rotates an epoch key so it can't follow future changes.
• Self-hostable. Ships serverless by default (public DHT + n0's free relays as fallback); run your own relay + discovery for full control (see infra/).
• Honest serverless. "No server that can read your data" — not zero-infra: a relay only ever forwards ciphertext. If all your devices are off, updates are pending, not lost.

See docs/PAIRING.md for the link flow and docs/PRIVACY.md for exactly what is and isn't stored.

Repository layout

mesh-engine/    the substrate: per-device identity, mainline-DHT discovery, relay
                fallback (or self-hosted), SPAKE2 pairing, N isolated encrypted Spaces,
                EndpointId membership + signed roles, epoch-key revocation + audit log,
                CRDT sync + multi-stream blob transfer, keychain keys + encrypted
                export. The ONLY crate that touches iroh / automerge.
mesh-mcp/       a tiny MCP host — implement one trait and an app's data + actions
                become readable/writable by any AI agent, with no server in the loop.
apps/memory/    agent-memory: portable, vendor-neutral memory (the memory schema).
apps/tabs/      centraltabs: cross-device tab/link sync.
apps/files/     kith-files: file sharing on the blob primitive.
apps/desktop/   ★ kith: the Tauri desktop app (GUI) + `kith serve` unified MCP server
                that runs all three apps on one shared engine.

The engine is the product; the apps are thin and share one Mesh (one identity, one pairing, one replica). See ROADMAP.md for invariants and what's next.

Security status — alpha (locally tested; not independently audited)

Enforced today, each with tests:

• ✅ Transport is end-to-end encrypted (iroh QUIC / TLS 1.3).
• ✅ Spaces are isolated — edits in one space never reach another, and a member of one space cannot sync or fetch blobs from another (two_spaces_isolated, cross_space_blob_isolation).
• ✅ Membership rooted in EndpointId + enforced roles — a team space's signed, hash-chained membership log binds its root Admin to the space id; a non-member is refused even with a leaked group key, and a Reader's writes are rejected by honest peers because every change carries its author's Ed25519 signature (non_member_endpointid_rejected_even_with_group_key, reader_write_rejected, membership_change_requires_admin).
• ✅ Revocation via epoch rekey — removing a device rotates an Admin-signed epoch key distributed only to remaining members, and re-keys at-rest data, giving post-removal confidentiality for future data (revoked_device_cannot_sync_new_epoch, remaining_members_get_new_key_and_converge, removed_device_cannot_fetch_blob).
• ✅ Tamper-evident audit log — the hash-chained membership log records the lifecycle and fails to load if altered (audit_log_hash_chain_detects_tampering).
• ✅ Keys in the OS keychain (Windows Credential Manager / macOS Keychain; hardened-file fallback on Linux) and an encrypted, passphrase-protected space export as the no-account recovery path (keychain_roundtrip, space_export_import_roundtrip).
• ✅ Account-free, mutual pairing via SPAKE2; the replica is XChaCha20-Poly1305 encrypted at rest.

Honest caveats (the path from alpha to "trust it broadly"):

• The crypto has not had an independent audit (and spake2 0.4 is itself unaudited). No coding pass substitutes for a review before trusting multi-human spaces with sensitive data.
• Revocation gives post-removal confidentiality for future data — it is not forward secrecy for data a removed device already synced, and not a retroactive wipe.
• Role enforcement holds against honest peers (an honest majority is assumed for liveness); a removed device keeps whatever it already has, and concurrent Admin edits are reconciled by longest-valid-chain, not full group-key agreement.
• On Linux (no keychain backend compiled) keys fall back to a hardened key file.
• Throughput is tuned for "good enough + resumable", not FASP/Aspera-class; BBR isn't applied (an upstream limitation — see docs/throughput.md).
• Real-NAT hole-punching and live-DHT/relay behavior are verified by hand, not in CI.

See SECURITY.md to report an issue.

License

Dual-licensed under MIT or Apache-2.0, at your option.