How do I set a custom field value for an Activity via the REST API?

I can create an activity on a contact. I am looking to set a value for a custom field within that activity as well.

For reference my current POST request looks something like this:


Any insight is appreciated! Thanks for the help!

1 Answer 1


You need to know the custom field ID of the field in question. If the ID is 14, you can use:


In general, if you're asking these sorts of questions, you can answer them best by using the API explorer: Help menu > Developer > API Explorer. You can use it to design your query, and it will build your REST string for you - including looking up custom field IDs.

To get the ID via the GUI, you can go to Administer menu > Customize Data and Screens > Custom Fields, then select "View and Edit Custom Fields" for the appropriate group. If you hover your mouse over the "Edit Field" link, you'll see a URL that ends in "&id=x". "x" is your field ID.

To get the field ID via the API, do a call to CustomField.get. Here's a REST call to get the ID of a field called "Mail Designation":

/sites/all/modules/civicrm/extern/rest.php?entity=CustomField&action=get&json={"sequential":1,"label":"Mail Designation"}&api_key=yourkey&key=sitekey

Better still, use CustomField.getvalue to return just the ID:

/sites/all/modules/civicrm/extern/rest.php?entity=CustomField&action=getvalue&json={"sequential":1,"return":"id","label":"Mail Designation"}&api_key=yourkey&key=sitekey
  • Jon, thanks for the answer and including that resource. I believe this is what I need. Cheers! -matt
    – mac
    Jun 19, 2015 at 20:03
  • Jon - a follow up. Any clue how to get the ID of a custom field via the api or GUI? Thanks for the help.
    – mac
    Jun 19, 2015 at 20:27
  • @mcphilly I edited my answer to include your follow-up question. Jun 25, 2015 at 15:38

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