What is in this PR

This PR implements four new runtime formulas: number_format(), abs(), null(), date_interval(), and to_datetime().

It also adds support for better human-readable error messages by adding a new getErrorMessage() method to the BaserowRuntimeFormulaArgumentType class, as well as refactoring the RuntimeFormulaFunction::validateArgs() to raise the error message if available. The backend has been similarly refactored.

Finally, a new skill create-update-runtime-formula AI skill has been added. This will make it easier to use an LLM to add/update a runtime formula with a simple prompt. For instance, to create the null() runtime formula, I just prompted:

I want you to create a runtime formula named null() that should simply return null in the frontend or None in the backend.

Closes #4974

How to test this PR

1. abs()

This simply returns the absolute value of a number, e.g. abs(-100) should return 100.

Create a Builder element, e.g. Heading, and using expert mode type in abs(-100). You should see 100 rendered.

2. null()

This returns a null (or None in the backend). This is useful when you need a null value to be used, e.g. when upserting a null to a row or evaluating it in a Router node, e.g.:

if(get('previous_node.40.0.field_2918') = null(), true, false)

Create a Date field in your database table and fill the field with a date value. Then in Builder or Automation, create an workflow action or a node that updates that row's field to use null() in the service. You should observe that the row's field is correctly set to null.

3. number_format()

This formats a number with the option to specify:

• Decimal places (defaults to 0)
• Thousand separator (defaults to ,)
• Decimal separator (default to .)

E.g. using number_format(12345, 2, '.', ',') should return 12.345,00.

4. date_interval()

This returns a timedelta that can be used by the existing add or minus formulas to operate on a date.

E.g. now() + date_format('1 day') should add a day to the current datetime.

5. to_datetime()

This takes a Moment.js datetime string with an optional date format, and converts it to a datetime objeect.

E.g. to_datetime('2026-06-04') returns datetime(2026, 06, 04, 0, 0, 0).

Checklist

• A changelog entry has been added to changelog/entries/unreleased using changelog/src/changelog.py
• New/updated Premium/Enterprise features are separated correctly in the premium or enterprise folder
• The latest Chrome and Firefox have been used to test any new frontend features
• Documentation has been updated
• Quality Standards are met
• Performance: tables are still fast with 100k+ rows, 100+ field tables
• The redoc API pages have been updated for any REST API changes
• Our custom API docs are updated for changes to endpoints accessed via API tokens
• The UI/UX has been updated following the UI Style Guide
• Security impact of change has been considered