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URL Prefilling for RSVP Forms

Populate RSVP form fields automatically from URL query parameters, so links in your emails and campaigns arrive with the name, email, and tracking data already filled in.

T
Written by Tom

You can prefill the fields on an event RSVP form by adding query parameters to the event URL. When someone opens the link, AddCal reads those parameters and fills in the matching fields. This reduces friction for guests and is useful for email campaigns, where your platform can merge each recipient's details into the link.

Prefilling the name and email fields

The built-in name and email fields fill in from these URL parameters:

  • form_name prefills the name field.

  • form_email prefills the email field.

The older parameters rsvp_name and rsvp_email still work and are kept for backward compatibility, so existing links keep working.

Examples

Basic usage:

https://addcal.co/e/your-event?form_name=John%20Doe&[email protected]

Mailchimp:

https://addcal.co/e/your-event?form_name=*|FNAME|* *|LNAME|*&form_email=*|EMAIL|*

Klaviyo:

?form_name={{ person.first_name }} {{ person.last_name }}&form_email={{ person.email }}

ConvertKit:

?form_name={{ subscriber.first_name }} {{ subscriber.last_name }}&form_email={{ subscriber.email_address }}

ActiveCampaign:

?form_name=%FIRSTNAME% %LASTNAME%&form_email=%EMAIL%

Custom query string fields

For anything beyond name and email, add a custom field that fills in from a URL parameter. Two field types support this:

  • query_string is visible on the form. It fills in from a URL parameter, and guests can see and change the value.

  • query_string_hidden is hidden from guests. It fills in from a URL parameter but never appears on the form, which suits tracking data such as UTM parameters or referral codes.

Configuring a query string field

When you add a query string field to a form, set:

  1. Field type: choose Query String or Query String (Hidden).

  2. Label: the text guests see (visible fields only).

  3. Query Parameter Name: the URL parameter to read the value from, for example utm_source. If you leave it blank, the field's slug is used.

Query string examples

UTM source tracking:

  • Field type: Query String (Hidden)

  • Query Parameter Name: utm_source

  • URL: ?utm_source=newsletter

  • Result: the field captures newsletter without showing it to the guest.

Referral code:

  • Field type: Query String

  • Label: Referral Code

  • Query Parameter Name: ref

  • URL: ?ref=FRIEND2024

  • Result: a Referral Code field shows, prefilled with FRIEND2024.

Campaign tracking:

  • Field type: Query String (Hidden)

  • Query Parameter Name: campaign_id

  • URL: ?campaign_id=summer2024

  • Result: campaign data is captured for your records without showing it to the guest.

URL encoding

Encode the values you put in URLs. Spaces become %20, and other special characters are encoded too. Most email platforms do this for you when you insert merge tags.

Tips for email campaigns

  1. Test your links before sending to your full list.

  2. Set fallback values in your email template so links still work when a recipient's data is missing.

  3. Keep URLs short for mobile readers.

  4. Use hidden query string fields to track which campaign or source each RSVP came from.

How prefilling is applied

  • The built-in parameters (form_name and form_email, or their rsvp_ equivalents) are read first, then custom query string fields.

  • Only empty fields are prefilled. If a guest has already entered a value, it is never overwritten.

  • Prefilling works with all custom RSVP forms, with default and custom appearances, and alongside every other field type.

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