All DDF provided directly with deCONZ typically reside in /usr/share/deCONZ/devices/ on a Linux system and are loaded first. However, files residing in the home directory of the user running deCONZ (e.g. /home/<DECONZUSER>/.local/share/dresden-elektronik/deCONZ/devices) will override the pre-packaged files to allow users to amend and keep their own files if desired.

More details about the DDF format and its processing can be found at:
https://dresden-elektronik.github.io/deconz-dev-doc/modules/ddf

There is a video too DDF description on deconz

And for reminder (extract from deconz documentation Deconz documentation ):

As simple as that: Select a node in deCONZ GUI with a left-click (this is important). Then right-click on the node to bring up the context menu as below, now select Edit DDF.

The items pane is the default view of the DDF editor and allows you to define exposure of a device via deCONZ REST API.

On the left-hand side, some general information regarding the associated device can be entered. Furthermore, you can see/define which light and sensor resources are created as well as the respective resource items for those. It depends if anything is shown at all for a particular device. Previously supported devices via legacy code should reflect the current state implementation (items available, but window title displays "untitled"), which must not necessarily be complete due to incomplete testing or insufficient information. Already supported devices via DDF also offer items and can be recognized as such by representing the respective JSON filename in the window title. Currently unsupported devices can be identified by either the respective node having a hex name (e.g. 0xA3E1) and/or just having the device item available.

Content	Description
	General, device specific information. See Edit device area (middle) for an overview of the associated options/fields.
	This allows you to adjust the device type and the unique ID of a subdevice/resource. See Edit subdevice area (middle) for an overview of the associated options/fields.
	This allows you to to configure the individual resource items exposed via REST API. Basically, this determines what is done on reception of data and/or what is written to the device. See Edit resource item area (middle) for an overview of the associated options/fields.

The right-hand side gives you a selection of all predefined light and sensor resources (colored in grey) as well as all available resource items. The aforementioned resources comprise a preselection of resource items based on experience, which should fit a device most of the time. However, selecting one and subsequently adding or removing predetermined resource items is always possible giving you a vast amount of freedom.

Content	Description
	States (in green) and Configs (in blue). WIP

In the middle, the individual items chosen on the left side can be configured.

In the middle, the individual items chosen on the left side can be configured.

In the middle, the individual items chosen on the left side can be configured.

Defaults

Defaults for the resource items are to be found in the respective item file in /usr/share/deCONZ/devices/generic/items, if any. E.g.: the resource item attr/modelid has a default parsing stanza. In that case, it is sufficient to have the below in the DDF for handling the model ID. Of course, the defaults can be overwritten for almost every resource item.

Endpoint

Try to use the good endpoint instead of "auto".

Scripts/Expressions

The above mentioned resource item files also contain a corresponding Script or Expression in case a function stanza is defined. If you wish or need to change the data processing, there're various deCONZ objects and methods which can be used. Taken from device_js.h:

    # Javascript API

    This API can be used in expressions in "parse" and "write" functions.
    Beside this anything can be used what is supported by QJSEngine.

    If a expression/script is too long to write it in the DDF file it could saved in an external
    file and referenced as "file://<path>/some-script.js" instead of an JS expression string.
    The file path is relative to the DDF file directory.

    ## Global objects accessible in evaluate() call

    Following globals are scoped to the surrounding item object in the DDF

    R        – access related Resource (Device | Sensor | LightNode)
    Item     — acces related ResourceItem
    Attr     — acces parsed deCONZ::ZclAttribute (if available in "parse")
    ZclFrame — access parsed deCONZ::ZclFrame (if available in "parse)

    ### Object Methods

    R.item(suffix) -> gets Item object, for example the 'config.offset'
    Item.val       -> ResourceItem value (read/write)
    Item.name      -> ResourceItem name like 'state/on' (read only)
    Attr.id        -> attribute id (number, read only)
    Attr.dataType  -> attribute datatype (number, read only)
    Attr.val       -> attribute value (read only)

    ZclFrame.cmd           -> ZCL command (read only)
    ZclFrame.payloadSize   -> ZCL payload size (read only)
    ZclFrame.isClCmd       -> cluster command (read only, 2.13.03?)
    ZclFrame.at(x)         -> value at position x (read only)

    ### under consideration (not implemented)
    R.parent --> get the parent resource object (Device)
    R.subDevice(uniqueId) --> get another sub-device resource object
    Item.lastSet --> timestamp when item was last set
    Item.lastChanged --> timestamp when item was last changed
    ZclFrame.attr(id) --> Attr object (if the ZclFrame has multiple)


    Example expressions:

    "parse"

        Item.val = Attr.val + R.item('config/offset').val
        Item.val = Attr.val
        Item.val = Attr.val << 16

    "write"

        let out = -1;
        if (Item.val === 'heat') out = 2;
        else if (Item.val === 'cool') out = 0;
        out; // becomes the result of the expression

Adding bindings is a convenient drag&drop experience. From the device of interest, drag the cluster of interest to the left area and drop it. This adds the cluster to the list. For the attribute of interest, drag the respective attribute, but this time, drop it in the middle area to add the attribute to the list. Lastly, configure the attribute with the values of choice and repeat the steps where necessary.