Hidden Fields

Hidden fields allow you to pass data to your surveys through URL parameters without displaying them to respondents. This is useful for tracking user segments, personalizing questions, and enriching response data.

How Hidden Fields Work

Hidden fields are:

Defined in the survey configuration
Passed via URL parameters when launching the survey
Stored with survey responses
Available for use in conditional logic and recall
Not visible to survey respondents

Enabling Hidden Fields

Open Survey Settings

Navigate to your survey in the editor and look for the “Hidden Fields” card (marked with an eye-off icon).

Add Field IDs

Enter field identifiers (e.g., userId, plan, source) that you want to capture.

Use in Survey URL

Append hidden fields to your survey URL as query parameters.

Configuration

Hidden fields are configured in the survey object:

{
  "hiddenFields": {
    "enabled": true,
    "fieldIds": ["userId", "email", "plan", "source", "campaign"]
  }
}

Reference: packages/database/zod/surveys.ts:109-116

Passing Hidden Fields via URL

When launching a survey, append hidden fields as URL parameters:

https://app.formbricks.com/s/survey123?
  userId=user_abc123&
  email=user@example.com&
  plan=premium&
  source=email&
  campaign=spring_2024

URL Encoding

Always URL-encode values containing special characters:

const hiddenFields = {
  userId: 'user_123',
  email: 'user@example.com',
  tags: 'VIP Customer, Enterprise'
};

const params = new URLSearchParams(hiddenFields);
const surveyUrl = `https://app.formbricks.com/s/survey123?${params.toString()}`;
// Result: ?userId=user_123&email=user%40example.com&tags=VIP+Customer%2C+Enterprise

Using Hidden Fields

In Conditional Logic

Branch survey flow based on hidden field values:

{
  "logic": [
    {
      "id": "logic_1",
      "conditions": {
        "id": "cond_1",
        "connector": "and",
        "conditions": [
          {
            "id": "cond_1_1",
            "leftOperand": {
              "type": "hiddenField",
              "value": "plan"
            },
            "operator": "equals",
            "rightOperand": {
              "type": "static",
              "value": "enterprise"
            }
          }
        ]
      },
      "actions": [
        {
          "id": "action_1",
          "objective": "jumpToBlock",
          "target": "enterprise_questions"
        }
      ]
    }
  ]
}

Reference: Logic type definitions at packages/types/surveys/logic.ts:77-80

In Question Text (Recall)

Personalize questions using hidden field values:

{
  "id": "welcome",
  "type": "openText",
  "headline": {
    "default": "Hi recall:userId, how can we improve your recall:plan experience?"
  }
}

The recall syntax recall:fieldId will be replaced with the actual value:

"Hi john_doe, how can we improve your premium experience?"

In Response Data

Hidden fields are automatically included in response data:

{
  "responseId": "resp_123",
  "surveyId": "survey_123",
  "data": {
    "question_1": "Great product!",
    "question_2": 5
  },
  "meta": {
    "userId": "user_abc123",
    "email": "user@example.com",
    "plan": "premium",
    "source": "email",
    "campaign": "spring_2024"
  }
}

Configuration Examples

Example 1: User Tracking

{
  "hiddenFields": {
    "enabled": true,
    "fieldIds": [
      "userId",
      "email",
      "accountId",
      "organizationId"
    ]
  }
}

Survey URL:

https://app.formbricks.com/s/abc123?
  userId=usr_789&
  email=sarah@company.com&
  accountId=acc_456&
  organizationId=org_123

Example 2: Marketing Attribution

{
  "hiddenFields": {
    "enabled": true,
    "fieldIds": [
      "utm_source",
      "utm_medium",
      "utm_campaign",
      "utm_content",
      "utm_term",
      "referrer"
    ]
  }
}

Survey URL:

https://app.formbricks.com/s/abc123?
  utm_source=google&
  utm_medium=cpc&
  utm_campaign=summer_sale&
  utm_content=ad_variant_a&
  utm_term=survey+software&
  referrer=google.com

Example 3: Product Context

{
  "hiddenFields": {
    "enabled": true,
    "fieldIds": [
      "productId",
      "productName",
      "category",
      "price",
      "inStock"
    ]
  }
}

Survey URL:

https://app.formbricks.com/s/abc123?
  productId=prod_9876&
  productName=Premium%20Subscription&
  category=SaaS&
  price=99&
  inStock=true

Example 4: User Segmentation

{
  "hiddenFields": {
    "enabled": true,
    "fieldIds": [
      "userType",
      "plan",
      "signupDate",
      "lastActiveDate",
      "totalPurchases"
    ]
  }
}

Survey URL with Logic:

https://app.formbricks.com/s/abc123?
  userType=power_user&
  plan=enterprise&
  signupDate=2023-01-15&
  lastActiveDate=2024-03-01&
  totalPurchases=42

Dynamic URL Generation

JavaScript Example

function generateSurveyUrl(baseUrl, hiddenFields) {
  const params = new URLSearchParams();
  
  Object.entries(hiddenFields).forEach(([key, value]) => {
    if (value !== null && value !== undefined) {
      params.append(key, String(value));
    }
  });
  
  return `${baseUrl}?${params.toString()}`;
}

// Usage
const surveyUrl = generateSurveyUrl(
  'https://app.formbricks.com/s/abc123',
  {
    userId: currentUser.id,
    email: currentUser.email,
    plan: currentUser.subscription.plan,
    source: 'dashboard'
  }
);

window.open(surveyUrl, '_blank');

React Example

import { useMemo } from 'react';

function SurveyButton({ user, source }) {
  const surveyUrl = useMemo(() => {
    const params = new URLSearchParams({
      userId: user.id,
      email: user.email,
      plan: user.plan,
      source: source,
      timestamp: Date.now()
    });
    
    return `https://app.formbricks.com/s/abc123?${params.toString()}`;
  }, [user, source]);
  
  return (
    <a href={surveyUrl} target="_blank" rel="noopener noreferrer">
      Take Survey
    </a>
  );
}

Python Example (Backend)

from urllib.parse import urlencode

def generate_survey_url(base_url, user_data):
    hidden_fields = {
        'userId': user_data.get('id'),
        'email': user_data.get('email'),
        'plan': user_data.get('subscription', {}).get('plan'),
        'source': 'email_campaign',
        'timestamp': str(int(time.time()))
    }
    
    # Remove None values
    hidden_fields = {k: v for k, v in hidden_fields.items() if v is not None}
    
    query_string = urlencode(hidden_fields)
    return f"{base_url}?{query_string}"

# Usage
survey_url = generate_survey_url(
    'https://app.formbricks.com/s/abc123',
    current_user
)

Validation & Constraints

Hidden field IDs must follow these rules (from packages/types/surveys/validation.ts):

Alphanumeric characters, hyphens, and underscores only
Cannot start with a number
Maximum length varies by implementation
Case-sensitive

Valid examples:

userId ✓
user_id ✓
user-id ✓
user123 ✓

Invalid examples:

123user ✗ (starts with number)
user id ✗ (contains space)
user@id ✗ (contains special character)

Practical Use Cases

Customer Support Surveys

Pass ticket ID, support agent, and issue category
Pre-fill customer information
Track survey source (email, in-app, SMS)

Product Feedback

Include feature name, version, and user role
Track which page/section triggered the survey
Segment by usage frequency or feature adoption

E-commerce

Pass product ID, category, and price
Include order number and purchase date
Track campaign attribution

SaaS Onboarding

Pass signup source and referrer
Include plan type and company size
Track onboarding step completion

Best Practices

Consistent Naming: Use consistent field names across all surveys (e.g., always userId, not sometimes user_id).

No Sensitive Data: Don’t pass passwords, tokens, or highly sensitive PII in URL parameters.

Plan Field Names: Define a standard set of hidden fields for your organization
URL Length Limits: Keep total URL under 2000 characters for browser compatibility
Validate Values: Sanitize and validate hidden field values on the backend
Document Fields: Maintain documentation of what each hidden field represents
Privacy Compliance: Ensure hidden fields comply with GDPR, CCPA, and other regulations
Test Encoding: Always test with special characters and international text

Preventing Deletion

Hidden fields cannot be deleted if they are:

Used in conditional logic (error shown at apps/web/modules/survey/editor/components/hidden-fields-card.tsx:81-94)
Referenced in recall syntax (error at lines 96-119)
Used in quotas (error at lines 121-131)
Used in follow-up actions (error at lines 133-142)

Implementation Reference

Hidden fields implementation:

UI component: apps/web/modules/survey/editor/components/hidden-fields-card.tsx:29
Type definitions: packages/database/zod/surveys.ts:109-116
Validation utilities: packages/types/surveys/validation.ts
Usage detection: apps/web/modules/survey/editor/lib/utils

Conditional Logic - Use hidden fields in branching logic
Webhooks - Hidden fields included in webhook payloads
Multi-Language - Combine with language detection

Survey Types

Question Types

Features

How Hidden Fields Work

Enabling Hidden Fields

Configuration

Passing Hidden Fields via URL

URL Encoding

Using Hidden Fields

In Conditional Logic

In Question Text (Recall)

In Response Data

Configuration Examples

Example 1: User Tracking

Example 2: Marketing Attribution

Example 3: Product Context

Example 4: User Segmentation

Dynamic URL Generation

JavaScript Example

React Example

Python Example (Backend)

Validation & Constraints

Practical Use Cases

Customer Support Surveys

Product Feedback

E-commerce

SaaS Onboarding

Best Practices

Preventing Deletion

Implementation Reference

Survey Types

Question Types

Features

Documentation Index

​How Hidden Fields Work

​Enabling Hidden Fields

​Configuration

​Passing Hidden Fields via URL

​URL Encoding

​Using Hidden Fields

​In Conditional Logic

​In Question Text (Recall)

​In Response Data

​Configuration Examples

​Example 1: User Tracking

​Example 2: Marketing Attribution

​Example 3: Product Context

​Example 4: User Segmentation

​Dynamic URL Generation

​JavaScript Example

​React Example

​Python Example (Backend)

​Validation & Constraints

​Practical Use Cases

​Customer Support Surveys

​Product Feedback

​E-commerce

​SaaS Onboarding

​Best Practices

​Preventing Deletion

​Implementation Reference

​Related Features

How Hidden Fields Work

Enabling Hidden Fields

Configuration

Passing Hidden Fields via URL

URL Encoding

Using Hidden Fields

In Conditional Logic

In Question Text (Recall)

In Response Data

Configuration Examples

Example 1: User Tracking

Example 2: Marketing Attribution

Example 3: Product Context

Example 4: User Segmentation

Dynamic URL Generation

JavaScript Example

React Example

Python Example (Backend)

Validation & Constraints

Practical Use Cases

Customer Support Surveys

Product Feedback

E-commerce

SaaS Onboarding

Best Practices

Preventing Deletion

Implementation Reference

Related Features