# Synchronization

Synchronization adapters are the “connectors” the orchestrator uses for syncing. Each adapter knows how to read a provider and how to write changes back.

Related: [CW Orchestrator](/blueprint-architecture/orchestrator.md).

### How to use this section

1. Connect providers in [Authentication](/crosswatch/providers/authentication.md).
2. Create a pair and enable a feature.
3. If a provider behaves oddly, open its adapter page below.

{% hint style="info" %}
Start with **one pair** and **one feature**. Then expand once the first run is clean.
{% endhint %}

### What adapters do

Adapters implement the same core flow:

* **Index**: fetch a present-state snapshot (what exists now).
* **Normalize**: turn provider rows into common items + stable IDs.
* **Apply**: add/remove/update on the target side.
* **Stabilize**: use local state to avoid repeats and flapping.

### Feature semantics (how to think about “changes”)

* **Watchlist**: set-like. Adds and removes are straightforward.
* **History**: event-like. `watched_at` matters. Duplicates are common.
* **Ratings**: numeric. Scale differences matter. Deletes can be destructive.
* **Playlists**: ordered. Often provider-specific. Not widely supported yet.

### Stability knobs (common patterns)

* Snapshot caching to reduce API load.
* Chunking + small pauses to avoid rate limits.
* Shadow/unresolved files to prevent endless retries.
* Activity/watermark logic for delta providers (example: SIMKL).

### Adapter guides

<table data-view="cards"><thead><tr><th>Adapter</th><th data-card-target data-type="content-ref">Open</th></tr></thead><tbody><tr><td>AniList</td><td><a href="/spaces/3rh5THg1PdhVsBt3GALo/pages/GUWl5kpWjOzbTroJ9EC0">/spaces/3rh5THg1PdhVsBt3GALo/pages/GUWl5kpWjOzbTroJ9EC0</a></td></tr><tr><td>CrossWatch (local backup)</td><td><a href="/spaces/3rh5THg1PdhVsBt3GALo/pages/wo1bvQ75vjpmwdLU5SbB">/spaces/3rh5THg1PdhVsBt3GALo/pages/wo1bvQ75vjpmwdLU5SbB</a></td></tr><tr><td>Emby</td><td><a href="/spaces/3rh5THg1PdhVsBt3GALo/pages/cHaK7elcPSgvo1VR2E48">/spaces/3rh5THg1PdhVsBt3GALo/pages/cHaK7elcPSgvo1VR2E48</a></td></tr><tr><td>Jellyfin</td><td><a href="/spaces/3rh5THg1PdhVsBt3GALo/pages/LVxifNNcUFwNIcZzn53r">/spaces/3rh5THg1PdhVsBt3GALo/pages/LVxifNNcUFwNIcZzn53r</a></td></tr><tr><td>MDBList</td><td><a href="/spaces/3rh5THg1PdhVsBt3GALo/pages/CsNqeI2L3uOOXg95AW06">/spaces/3rh5THg1PdhVsBt3GALo/pages/CsNqeI2L3uOOXg95AW06</a></td></tr><tr><td>Plex</td><td><a href="/spaces/3rh5THg1PdhVsBt3GALo/pages/OWAe360aTxSHXAnIiRoW">/spaces/3rh5THg1PdhVsBt3GALo/pages/OWAe360aTxSHXAnIiRoW</a></td></tr><tr><td>SIMKL</td><td><a href="/spaces/3rh5THg1PdhVsBt3GALo/pages/eqXoLy9ij0AlCf3sbYdg">/spaces/3rh5THg1PdhVsBt3GALo/pages/eqXoLy9ij0AlCf3sbYdg</a></td></tr><tr><td>Trakt</td><td><a href="/spaces/3rh5THg1PdhVsBt3GALo/pages/bRhLnM3fO7uDpCByQXcs">/spaces/3rh5THg1PdhVsBt3GALo/pages/bRhLnM3fO7uDpCByQXcs</a></td></tr><tr><td>Tautulli (history import)</td><td><a href="/spaces/3rh5THg1PdhVsBt3GALo/pages/7R7JVYBKElUh131kNRvA">/spaces/3rh5THg1PdhVsBt3GALo/pages/7R7JVYBKElUh131kNRvA</a></td></tr></tbody></table>

### Troubleshooting quick checks

* **Adds keep reappearing**: provider didn’t “stick” the write. Check adapter state files.
* **Recent changes not syncing**: reduce caching, or force a fresh read if supported.
* **429 / 5xx errors**: reduce chunk size, add delay, run less often.
* **Mismatches**: add [Metadata](/crosswatch/providers/metadata.md) and prefer stable IDs.

### Related topics

* [Syncing](/getting-started/first-time-setup/what-do-you-need/syncing.md) — step-by-step setup.
* [Best practices](/getting-started/best-practices.md) — safe defaults.


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# Agent Instructions: Querying This Documentation

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Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://wiki.crosswatch.app/crosswatch/providers/synchronization.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.