What is a custom field, and when to use it

All HR systems are inherently limited in the number of standard fields they can offer. This can become a problem if your product relies on additional information, which is not standard across all tools.

Initially, HR systems started adding an increasing number of standard fields to their systems. This quickly became a problem, and as the number of fields grew to hundreds, the systems became hard to maintain.

Custom fields are a way to solve this problem. They allow users to add new fields to the standard data model. By now, most HR systems have adopted this concept and offer custom fields.

How to use custom fields in an HR system

We offer a simple way to read custom fields from your HR system. The first step is to set it up in your system.


Let’s take Personio as an example:

Under Settings > Employee Information, you can easily add new attributes or entire sections to your employee profiles. We will add a new attribute called “Favorite Color” to the “Public Profile” section.


If we now go to the profile of an employee, we can see the new field. Let’s set a value for it.


In the case of Personio, we need to let the API key know that we want to expose the new custom field. Just go to Settings > API Credentials and click on the API key you used to connect to Kombo. Then, open the “Readable employee attributes” section and select the new custom field.


Don’t forget to click save, and that’s it!

Setting up custom fields in Kombo

Before we set up the custom field in Kombo, let’s talk about how you will receive the data.

Data format

Each model that supports custom fields has a custom_fields attribute. This attribute is a JSON object that contains all custom fields. You can define a name for the custom field in Kombo, which will be used as the key in the JSON object.

You can then map any property from an integration to that custom field in Kombo. This allows you to unify the data across different integrations. Let’s say you have a customer with a custom field called “Favorite Color” and another customer with a custom field called “Favourite Colour”. You can map both of them to the same custom field in Kombo so that you can always access the data in the same way.

Setting up the custom field

Open the Dashboard and click on “Configuration” in the sidebar, then on the “Custom Fields” tab. There, you can create a new custom field. Let’s call it “fav_color”.


Here you can see how many integrations use this field and all the aliases that you have defined for this field.

Aliases are used to automatically map custom fields from integrations to your custom field. You can add as many aliases as you want.

When an alias matches the name of a custom field from an HR system, its value will automatically be mapped to your Kombo custom field. This allows you to mostly automate the process of mapping custom fields. In regards to our previous example in Personio, if you would have set up an alias called “Favorite Color”, the next sync would have automatically mapped the Personio value to your Kombo custom field.


If you want to map a custom field manually, you need to open the overview for that integration.

We will only discover custom fields after a sync has run, so make sure to click the “Sync now” button after setting up the custom field in the HR system. After the sync is finished, you can open the custom field dropdown and select the custom field you want to map. Don’t forget to click “Update mappings” to save your changes.


After creating your desired mapping, the next sync will match the value of the API response to the Kombo custom field. Your next request to Kombo will contain the custom field.

Accessing custom fields in the API

When you query the API, you will receive any mapped custom field values in the custom_fields attribute. In this case, we query the GET /employees endpoint. The value of a custom field mirrors what is returned by the underlying API (i.e. it’s not always a string but can be a number or even an object too).

  "status": "success",
  "data": {
    "results": [
        "custom_fields": {
          "fav_color": "blue"
          "manager": {
            "name": "Frank"
          "reports": [
              "name": "Tom"