# Content sources
> Understand how content source providers store and load table collections and their assets.
Understand how content source providers store and load table collections and their assets.
A content source decides how the project stores localized content, how it ships in a build, and how it loads at runtime. Each table collection is assigned to one source. In the API, sources are [`IAssetProvider`](/engine/6000.7/script-reference/unity/localization/providers/iassetprovider.md) implementations that return the requested localized content, and they live in the Localization settings as an ordered list.
## The source chain
{ /* Mermaid source kept for the future doc platform; shown as the static image below until mermaid rendering is supported. */ }
```mermaid
flowchart TD
req["Request: table or asset by address"]
chain["AssetProvider chain"]
p1["Direct references
(ReferencedAssetProvider)"]
p2["Resources folder
(ResourceFolderProvider)"]
p3["Data files (JSON)
(JsonResourceProvider)"]
val["First source that serves the address wins"]
req --> chain
chain --> p1
chain --> p2
chain --> p3
p1 --> val
p2 --> val
p3 --> val
classDef code fill:#F5F5F5,stroke:#BDBDBD,color:#111;
class req,chain,p1,p2,p3,val code;
linkStyle default stroke:#2196F3,stroke-width:1.5px;
```
**Requests walk the content source list until a source serves the address.:**
The Localization settings hold an ordered list of sources ([`AssetProvider`](/engine/6000.7/script-reference/unity/localization/providers/assetprovider.md)). A request walks the list until a source serves it. The list allows one source of each type, and **Default for new collections** controls which source Unity assigns a new collection to.
## Built-in sources
Localization provides the following content sources. You can enable them by adding them to your **Content sources** list in the [Localization settings reference](/engine/6000.7/manual/localization/settings-reference.md).
| **Source** | **Description** |
| --------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| **Direct references** | The settings hold direct references to the collection's tables, and asset entries reference their assets. Everything loads synchronously with the settings. This is the simplest option and works best when all localized content can sit in memory. |
| **Resources folder** | Tables and assets load from `Resources` folders by path, on demand, synchronously or asynchronously. A collection saved under a `Resources` folder belongs to this source. |
| **Data files (JSON)** | Tables ship as JSON files in `StreamingAssets` instead of assets, so translators can edit them and builds can gain languages after release. Refer to [Data file tables](/engine/6000.7/manual/localization/content-storage-and-loading/data-file-tables.md). |
| **Addressables** | Tables and assets load through the Addressables system. Available if you install version 2.0 of the `com.unity.localization` package. |
> **Note:**
>
> Everything under a `Resources` folder is included with the build, including tables for disabled locales. The settings page warns when this applies.
## How Unity assigns a source to a collection
Each collection records the source that serves it. For most sources, the collection asset's Editor window shows a source dropdown, and changing the dropdown re-registers the collection's tables with the new source in one undo step. No files move on disk.
The **Resources folder** source is different: membership follows the collection's location, so the source dropdown doesn't include it. A collection saved under a `Resources` folder belongs to this source, and moving the assets out of `Resources` moves it off. Unity re-registers the collection whenever the assets move.
A collection's assignment and location can disagree, for example a collection under `Resources` that's assigned to another source. When this happens, the collection's **Inspector** window shows a warning with a button that fixes the assignment.
## Asset entries and sources
String entries live in the table, so the source only affects how Unity stores the table itself. For asset entries, you also need to decide how Unity stores each asset. That decision is per entry, not per source. A **Direct** entry references the asset, and a **Resources** entry stores a path. Refer to [Localize assets](/engine/6000.7/manual/localization/translations/localize-assets.md).
## Custom sources
Content that lives somewhere the built-in sources can't reach, for example downloaded content or a mod folder, needs a custom source. A custom source is a runtime [`IAssetProvider`](/engine/6000.7/script-reference/unity/localization/providers/iassetprovider.md) that supports one or both loading paths ([`IAsyncAssetProvider`](/engine/6000.7/script-reference/unity/localization/providers/iasyncassetprovider.md), [`ISynchronousAssetProvider`](/engine/6000.7/script-reference/unity/localization/providers/isynchronousassetprovider.md)), paired with an Editor companion that registers collection content with the provider when you assign a collection to it. Requests arrive as an [`AssetKey`](/engine/6000.7/script-reference/unity/localization/providers/assetkey.md) that carries the address and expected type.
For a complete example, refer to [Create a custom asset provider](/engine/6000.7/manual/localization/examples/example-custom-asset-provider.md). To add a custom table file format instead, refer to [Create a file table provider for text files](/engine/6000.7/manual/localization/examples/example-text-file-table-provider.md).
## Additional resources
* [Data file tables](/engine/6000.7/manual/localization/content-storage-and-loading/data-file-tables.md)
* [Localize assets](/engine/6000.7/manual/localization/translations/localize-assets.md)
* [Create a custom asset provider](/engine/6000.7/manual/localization/examples/example-custom-asset-provider.md)