---
title: "Cloud Sync (cmem.ai Pro)"
description: "Two-lane multi-device sync of your memory database — durable HTTP push/pull through a per-user sync hub, with an optional WebSocket speed layer."
---

# Cloud Sync (cmem.ai Pro)

Cloud sync replicates your local memory database across your devices through a
**per-user sync hub** — an ordered log of everything your devices write. It is
built into the worker: **there is no daemon — the worker syncs on write**. The
same process that records every observation also uploads it, and pulls the
other devices' writes back down.

<Note>
**Two lanes, one source of truth.** Everything durable travels over plain
HTTP: pushes append to the hub's ordered log, pulls page through it with a
cursor. An optional WebSocket rides alongside as a pure *speed layer* — it
only makes the next pull happen sooner. The socket can be dropped, disabled,
or wrong with **zero data loss**; the HTTP cursor is always the truth.
</Note>

## What syncs

Three kinds of rows are replicated between your devices:

- **Observations** — the compressed memories claude-mem generates from your sessions.
- **Session summaries** — the per-session overview records.
- **User prompts** — the prompts you typed (clamped to 200&nbsp;KB per field).

Alongside the rows, three kinds of **mutations** travel through the same log
so later edits converge everywhere: session **title** changes, **prompt→session
repairs** (a prompt captured before its session registered is re-linked on
every device), and **project remaps** (worktree adoption and cwd-based moves
retarget the affected rows on every device).

<Warning>
**Privacy:** cloud sync uploads your observation narratives and your full
prompt text to the sync hub under your cmem.ai account. Don't enable it if
that content must stay on your machine.
</Warning>

## How the push lane works

**The database is the queue.** Every synced table carries a `synced_at` column
(`NULL` = not in the log yet). After each write, the worker nudges a debounced
flusher that drains `WHERE synced_at IS NULL` and stamps rows on success. That
one mechanism handles live sync, offline catch-up, and retry. Rows written
after the SyncHub launch boundary start as `NULL`; anything that fails to
upload stays `NULL` until a later flush picks it up. Pre-launch local rows are
not treated as a cloud migration corpus.

- **Debounced:** write bursts coalesce; the flusher runs ~1.5&nbsp;s after the
  last write (250&nbsp;ms while the speed layer is connected), and only one
  flush runs at a time.
- **Batched:** ops drain in requests of up to 500 ops / 4,000,000 encoded
  bytes. Each individual canonical body is capped at 256,000 encoded bytes.
- **Timeboxed:** every request has a 30&nbsp;s timeout — a dead network can
  never hang the worker.
- **Retrying:** a failed upload leaves rows `NULL` and retries on the next
  write plus a capped exponential backoff (30&nbsp;s → 10&nbsp;min). The write
  path is never blocked — sync failures cost nothing but delay.
- **Idempotent:** the hub dedupes on origin identity, so a retried push can
  never create duplicates.

## How the pull lane works

Each device keeps a **cursor** into the hub's log and pulls everything after
it — in pages, so a device that was offline for a week (or is brand new and
starts from zero) catches up the same way an active one stays current:

- **Session start:** the worker pulls immediately before injecting context
  (bounded to 1.5&nbsp;s, so a dead network can't stall your session), which
  means memory written on another machine is there the moment you start
  working.
- **Steady state:** a short poll every 30&nbsp;s while a session is active,
  every 5&nbsp;min when idle, suspended entirely after an hour of no activity.
  Every push response also reports the log head, so an active device learns
  about remote writes without waiting out the timer.
- **Applied like native writes:** pulled rows keep their original timestamps,
  carry their origin device, index into full-text and vector search through
  the same paths native writes use, and are stamped so they can never be
  echoed back up.

## The speed layer (optional WebSocket)

When enabled (the default), the worker also holds one WebSocket to the hub and
receives new ops the moment another device pushes them — multi-device
convergence in well under a second instead of a poll interval. The socket is
strictly **advisory**: any anomaly (a gap, a parse error, a dropped
connection) simply closes it and runs one HTTP pull, which is always correct.
Set `CLAUDE_MEM_CLOUD_SYNC_WS` to `false` to turn it off — sync stays fully
correct at poll latency.

The hub can also ask every client to fall back to polling by stamping
responses with an `X-Sync-Mode: poll` header (an operational brake on the
server side). Clients close their sockets and keep syncing over HTTP —
degraded means *slower*, never *stopped* — and resume the socket automatically
when the header disappears.

## Requirements and setup

Cloud sync is active when **all three** of the token, the user id, and the hub
URL are non-empty — there is no separate enable flag; blank any one of them to
turn sync off.

1. A **cmem.ai Pro sync token and user id** (from **cmem.ai → Connect**).
2. A **sync hub URL** in `CLAUDE_MEM_CLOUD_SYNC_HUB_URL`. The hub is a
   Cloudflare Workers service (source in `workers/sync-hub/` with its own
   deploy runbook); use the hub URL your cmem.ai account documentation
   provides for it.

Run the `/cloud-sync` skill in Claude Code to check status and walk through
setup. It writes the settings into `~/.claude-mem/settings.json` (mode
`0600`) without ever echoing the token, restarts the worker, and verifies the
installed client can reach SyncHub.

## Settings

| Key | Default | Meaning |
|-----|---------|---------|
| `CLAUDE_MEM_CLOUD_SYNC_TOKEN` | `''` | Your cmem.ai sync token (from **cmem.ai → Connect**). Sent as `Authorization: Bearer`. |
| `CLAUDE_MEM_CLOUD_SYNC_USER_ID` | `''` | Your cmem.ai user id (from **cmem.ai → Connect**). All your devices share it — it names your hub log. |
| `CLAUDE_MEM_CLOUD_SYNC_HUB_URL` | `''` | Sync hub base URL. **Empty = sync off.** |
| `CLAUDE_MEM_CLOUD_SYNC_WS` | `'true'` | Advisory WebSocket speed layer. `'false'` = HTTP polling only; sync stays fully correct at poll latency. |
| `CLAUDE_MEM_CLOUD_SYNC_DEVICE_ID` | `''` | Stable identity of this machine. A fresh UUID is minted and persisted on first start. Don't edit it: every row is attributed to its origin device. |
| `CLAUDE_MEM_CLOUD_SYNC_DEVICE_NAME` | machine hostname | Human-readable label for this device. |

A Hub accepts at most 64 distinct device ids per account. Existing devices
continue to sync normally at the limit; a new device receives
`409 device_limit_exceeded`. Status/metadata reads and renaming an unknown
device do not create phantom devices.

## Status endpoint

The worker exposes `GET /api/sync/status` (on the same port as the rest of the
worker HTTP API). It is registered unconditionally, so an unconfigured install
answers `200` rather than a `404` — callers can tell "not set up" apart from
"worker down".

```bash
curl -s "http://127.0.0.1:${CLAUDE_MEM_WORKER_PORT}/api/sync/status"
```

Configured:

```json
{
  "configured": true,
  "deviceId": "2f6b1c9e-7d41-4c1a-9b0e-3d5f8a2c6e10",
  "pending": { "observations": 0, "summaries": 0, "prompts": 2, "mutations": 0, "tombstones": 0 },
  "quarantine": { "count": 0, "latestReason": null },
  "lastFlushAt": 1783981042731,
  "lastError": null,
  "hub": {
    "checkedAt": 1783981042800,
    "reachable": true,
    "epoch": "1783981042000",
    "headSeq": "42",
    "projectedSeq": "42",
    "error": null
  }
}
```

Every configured status request makes an authenticated, read-only
`GET /v1/sync/status` directly to SyncHub, including when all pending counts
are zero. The probe does not append an operation or advance a pull cursor.
`hub.reachable: false` and `hub.error` therefore expose a bad token, wrong Hub
URL, malformed response, timeout, or network failure
that an empty queue would otherwise hide.

- `pending` — rows (and queued mutation ops) still waiting to upload. Counts
  near 0 mean the hub's log has everything this device wrote.
- `lastFlushAt` — epoch ms of the last successful flush, `null` before the first.
- `lastError` — message from the most recent failed flush, `null` when healthy.
  It never contains the token.
- `hub` — the most recent authenticated SyncHub probe. Treat
  `hub.reachable: true` as the connectivity check; `lastError: null` alone is
  not enough. Sequence and epoch fields remain decimal strings.

Not configured:

```json
{ "configured": false }
```
