Are changes to Custom Fields tracked in Trello Card activity logs?

[Harry Samuel]

I am considering upgrading to Business Class and implementing a Custom Field to solve a specific use case which I have. The field I plan to implement will be an integer value, and I want to ensure that whenever that value changes, that change is reflected with a datetime-stamp in the Activity Log for the card so there's a clear audit trail. My assumption would be that the answer to this question is yes, but I want to check before proceeding as if it doesn't then I might look at other solutions to my problem.

[Felix]

Yes, changes to custom field items generates a "action" on the card. On the card-back, in the activity log, Trello will show you that a given user has updated a custom field, but it won't (currently) show from/to what the value was changed.

This data is available via the API.

A request like https://trello.com/1/cards/:idCard/actions?filter=updateCustomFieldItem will show you the custom field item updates on the card.

[redeyemounts]

Is there a turn around time on it being visible INSIDE the card activity? This should be possible as it is an activity.