> ## Documentation Index
> Fetch the complete documentation index at: https://private-7c7dfe99-fix-nav-issues.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# YAMLRegExpTree dictionary source

> Configure a YAML file as a source for regular expression tree dictionaries.

export const CloudNotSupportedBadge = () => {
  return <div className="cloudNotSupportedBadge">
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                <path strokeWidth="1.5" d="M2.66699 14L12.0003 4.66663" stroke="currentColor" strokeLinecap="round" strokeLinejoin="round" />
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        </div>
            Not supported in ClickHouse Cloud
        </div>;
};

The `YAMLRegExpTree` source loads a regular expression tree from a YAML file on the local filesystem.
It is designed exclusively for use with the [`regexp_tree`](/reference/statements/create/dictionary/layouts/regexp-tree) dictionary layout
and provides hierarchical regex-to-attribute mappings for pattern-based lookups such as user agent parsing.

<Note>
  The `YAMLRegExpTree` source is only available in ClickHouse Open Source.
  For ClickHouse Cloud, export the dictionary to CSV and load it via a [ClickHouse table source](/reference/statements/create/dictionary/sources/clickhouse) instead.
  See [Using regexp\_tree dictionaries in ClickHouse Cloud](/reference/statements/create/dictionary/layouts/regexp-tree#use-regular-expression-tree-dictionary-in-clickhouse-cloud) for details.
</Note>

<h2 id="configuration">
  Configuration
</h2>

```sql theme={null}
CREATE DICTIONARY regexp_dict
(
    regexp String,
    name String,
    version String
)
PRIMARY KEY(regexp)
SOURCE(YAMLRegExpTree(PATH '/var/lib/clickhouse/user_files/regexp_tree.yaml'))
LAYOUT(regexp_tree)
LIFETIME(0);
```

Setting fields:

| Setting | Description                                                                                                                                      |
| ------- | ------------------------------------------------------------------------------------------------------------------------------------------------ |
| `PATH`  | The absolute path to the YAML file containing the regular expression tree. When created via DDL, the file must be in the `user_files` directory. |

<h2 id="yaml-file-structure">
  YAML file structure
</h2>

The YAML file contains a list of regular expression tree nodes. Each node can have attributes and child nodes, forming a hierarchy:

```yaml theme={null}
- regexp: 'Linux/(\d+[\.\d]*).+tlinux'
  name: 'TencentOS'
  version: '\1'

- regexp: '\d+/tclwebkit(?:\d+[\.\d]*)'
  name: 'Android'
  versions:
    - regexp: '33/tclwebkit'
      version: '13'
    - regexp: '3[12]/tclwebkit'
      version: '12'
    - regexp: '30/tclwebkit'
      version: '11'
    - regexp: '29/tclwebkit'
      version: '10'
```

Each node has the following structure:

* **`regexp`**: The regular expression for this node.
* **attributes**: User-defined dictionary attributes (e.g. `name`, `version`). Attribute values may contain **back references** to capture groups in the regular expression, written as `\1` or `$1` (numbers 1-9). These are replaced with the matched capture group at query time.
* **child nodes**: A list of children, each with its own attributes and optionally more children. The name of the child list is arbitrary (e.g. `versions` above). String matching proceeds depth-first: if a string matches a node, its children are also checked. Attributes of the deepest matching node take precedence, overriding equally named parent attributes.

<h2 id="related-pages">
  Related pages
</h2>

* [regexp\_tree dictionary layout](/reference/statements/create/dictionary/layouts/regexp-tree) — layout configuration, query examples, and matching modes
* [dictGet](/reference/functions/regular-functions/ext-dict-functions#dictGet), [dictGetAll](/reference/functions/regular-functions/ext-dict-functions#dictGetAll) — functions for querying regexp tree dictionaries