Field validation

Field validation ensures that the data collected in your flows meets defined formatting, business, and quality requirements. Formsort supports both built-in and custom validators.

Built-in Validators

Formsort includes many default validators for common input types:

• Number questions: Enforce min/max value, integer constraints, and step intervals.

• Email fields: Automatically validate email formatting.

• Text fields: Can be configured with length or character restrictions.

These default validators cover the most common cases. For advanced use cases, custom validators are available.

Custom Validators (Enterprise Only)

Custom validators allow you to define your own validation logic using regular expressions, custom code, or asynchronous API calls. They are defined at the workspace level and can be reused across flows.

Defining Custom Validators

Custom validators are composed of two main parts:

1. Validator Metadata

Metadata includes:

• Name and description (used for identification in the Studio)

• Answer type (e.g., string, number, object) – this controls which questions or variables can use the validator

2. Validation Rules

Validators can contain multiple rules. Each rule must pass for the value to be considered valid.

Rule Severity

• Error: Blocking. The responder cannot proceed unless the input is corrected.

• Warning: Non-blocking. The responder is alerted, but may choose to proceed.

Regular expression rules

Regular expressions (regex) are available only for string inputs. You can create rules for inputs that must match or must not match a given pattern.

Example: Twitter Handle Validator

Custom code rules

For more flexibility, you can write custom validation functions using TypeScript.

Example:

function myFunction(value: string): ValidatorResult | undefined { // readonly line
  if (value.match(/admin|twitter/i)) {
    return {
      severity: 'error',
      message: 'Handle cannot contain the words "admin" or "twitter"'
    }
  }
  if (value.match(/[^a-zA-Z0-9_]/)) {
    return {
      severity: 'error',
      message: 'A username can only contain alphanumeric characters (letters A-Z, numbers 0-9) with the exception of underscores.'
    }
  }
  if (value.length > 15) {
    return {
      severity: 'error',
      message: 'Usernames cannot be more than 15 characters long'
    }
  }
}

• Return a ValidatorResult when the input is invalid.

• Return undefined when input passes validation.

Async custom code

Enable async mode to fetch data from external sources during validation using await.

Example (hypothetical Twitter handle check):

function myFunction(value: string): Promise<ValidatorResult | undefined> { // readonly line
  const res = await fetch('https://api.twitter.com/check-handle');
  const handleInfo = await res.json();
  if (handleInfo.taken) {
    return {
      severity: 'error',
      message: 'This handle has already been registered'
    }
  }
}

Testing validators

Use the Test tab to try out inputs and preview validation behavior:

• Regex rules: All rules are evaluated in parallel. Violations for each rule are shown independently.

• Custom functions: Only the first failed check is returned.

Examples:

Using the Regular Experssion UI (described above) has the added benefit of evaluating all rules concurrently, and outputting an error message for each rule that is violated:

Using custom validators in a flow

Once created, custom validators become selectable in Question settings (if the question’s data type matches the validator).

Updating custom validators

You can modify validators at any time. However:

• Flows using the validator need to be redeployed to pick up changes.

• Use the Show usages option to view which flows depend on a validator.

Deleting Validators

Custom validators can be deleted from the validator list.

• Flows already using the validator will continue to function.

• Deleted validators will no longer be available to assign to new questions or answers.