# Webhooks

NDI Bridge Service supports change subscriptions which allow you to observe changes to any value instead of polling. To register a webhook, append the following path to the target API value where the `callback` query parameter is set to the URL you wish to receive POST requests from:

`/subscribe?callback=https://myurl`

For instance, if you wanted to subscribe to changes on the host port value you would do:

`api/host/port/subscribe?callback=https://myurl`

If a subscription is successful, you will revive a GUID as a response. This GUID is the handle for your subscription. If you want to unsubscribe from any change subscription you call the following URL (do not appended to the target API path) with the `id` query parameter being set to the GUID you received from the subscribe response:

`http://localhost:8080/api/unsubscribe?id=`

Change subscriptions are POSTed to the callback URL as JSON with *key* being the target API path (like `host/port` ) and *value* being the current value or ”Value changed.” for security sensitive values.

Active webhooks can be seen under the **Webhooks** section of the web interface.

![Command Line Interface](/files/fF8j9GaJLSxet5bNLVD6)


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