> ## Documentation Index
> Fetch the complete documentation index at: https://docs.landerlab.io/llms.txt
> Use this file to discover all available pages before exploring further.
# Prefill Fields Using URL Parameters
> Prefill form fields using URL parameters to personalize user experience, reduce friction, and improve conversion rates.
LanderLab allows you to automatically **prefill fields in your quiz or form using URL parameters**. This helps reduce friction, personalize the experience, and improve conversion rates by filling in data you already have.
This feature is **enabled by default** - no extra setup is required beyond matching field names.
***
## How It Works
When a visitor lands on your page with parameters in the URL, LanderLab:
1. Reads the parameters from the URL
2. Matches them with input field Names
3. Automatically fills the matching fields
Matching is **not case-sensitive**, so different variations will still work.
***
## Example
URL:
```text theme={null}
https://yourlandingpage.com/?zip=12345
```
Setup:
* Parameter → `zip`
* Value → `12345`
* Input Name → `zip`, `Zip`, or `ZIP`
Result:
The Zip Code field is automatically filled with **12345** when the page loads.
***
## How to Set It Up
1. Identify the parameter you want to use (e.g. `email`, `zip`, `aff_id`)
2. Open your quiz or form in LanderLab
3. Select the input field you want to prefill
4. Set the **Name** of the input to match the parameter
5. Publish your page
6. Test using a live URL with parameters
***
## Common Use Cases
* **Location targeting**
```text theme={null}
?zip=90210
```
* **Email personalization**
```text theme={null}
?email=user@example.com
```
* **Affiliate tracking**
```text theme={null}
?aff_id=123
```
* **Campaign tracking (UTMs)**
```text theme={null}
?utm_source=facebook&utm_campaign=summer
```
***
## Important Notes
* Prefill works **only on the live (published) page**, not inside the builder preview
* Input Name must match the parameter exactly (no extra spaces)
* URL parameters must be properly formatted and encoded
* Matching is case-insensitive
**Tip:** Combine prefill with Hidden Fields and tracking to automatically capture attribution data without asking users to fill it manually.