# Expression Builder
## Overview
The Expression Builder is a visual tool for creating webhook filters without writing code. Filter your webhook notifications to only receive updates that match specific criteria.
**Available when creating and maintaining:**
* Webhook subscriptions [(API documentation)](https://api.dataloy.com/dataloy-rest-api/webhooks)
* Subscription templates
**Example**: Instead of getting notified about all voyage updates, only get notified for voyages with status "Nominated" or voyages longer than 30 days.
## Add Your First Condition
1. Click **+ Add Condition**
2. Click field to open the field selector and select a "Field" (e.g., `voyageHeader.voyageStatus.statusTypeDesc`).
3. Choose an "Operator" (=, >, <, etc.)
4. Enter the "Value" (e.g., "Nominated")
{% hint style="info" %}
Notice the expression preview: `voyageHeader.voyageStatus.statusTypeDesc = "Nominated"`
{% endhint %}
## Add Multiple Conditions
Click **+ Add Condition** again to add more filters:
* By default, conditions use **"Match all"** (AND logic) – both must be true
* Switch to **"Match any"** (OR logic) – either condition can be true
**Match all example**: `statusTypeDesc = "Nominated" AND daysCanal > 1`\
**Match any example**: `statusTypeDesc = "Nominated" OR daysCanal > 1`
## Create Groups for Complex Logic
Click **+ Add Group** to create parentheses around conditions:
**Result**: `daysCanal > 1 AND (daysTotal < 10 OR daysTotalAtSea < 5)`
## Compare to Field
Instead of comparing to a static value, you can compare one field to another field by toggling **Compare to Field**.
**Use case**: Get notified when loading takes longer than discharging:
```
daysLoading > daysDischarging
```
## Previous vs Current Values
When subscribing to updates, you can compare current and previous field values:
* **Previous**: The field value before the update
* **Current**: The field value after the update
**Example**: If voyage daysLoading change from 2.3 to 2.5:
* Previous value = 2.3
* Current value = 2.5
Get notified when loading days increases:
```
prev.daysLoading < daysLoading
```
