# Valid Values
The Valid Values feature in Decision Tables plays a crucial role in maintaining the integrity and accuracy of your data. By restricting cell entries to a predefined set of valid options, you can prevent errors and ensure consistency across your decision-making processes.
Valid values can be defined in three ways:
1. **Value** - A predefined list of allowed values in specific column.
2. **Regex** - Pattern-based validation using regular expressions.
3. **Lookup Table Reference** - Values from another Lookup Table.
This functionality enhances the reliability of your tables, streamlines data entry, and establishes clear guidelines for data input, fostering a more dynamic and responsive decision-making environment.
## How to Apply Valid Values
1. Click the **arrow icon** in the header of the column.
2. Select **Valid Values**.
3. A modal will open with three validation type tabs: **Value**, **Regex**, and **Lookup Table Reference**.
4. Choose your validation type and configure it (see sections below).
5. Click **Save values** to apply.
{% hint style="warning" %}
Valid Values **apply to simple cells only**.
Valid values **do NOT apply** when a cell is set to **function mode**.
Valid values **cannot be set** for **calculated columns** (calc columns are always in function mode).
{% endhint %}
### **Validation Type 1: Value (Predefined List)**
Define a specific list of allowed values for the column.
**How to set up:**
1. Open the Valid Values modal.
2. Select the **Value** tab.
3. Type valid value and **press Enter to confirm**.
4. Repeat for all allowed values.
5. Click **Save values**.
Once valid values are applied, every cell (except for functions) in the column is checked against the predefined list. If a cell contains an invalid value, it will be flagged.
Additionally, when valid values are set, you cannot directly type into the cells in that column. Instead, a dropdown with the list of valid values will appear when you click on a cell, allowing you to select the appropriate value.
{% hint style="success" %}
You can use not just simple values, but also variables, dates, or even full expressions as valid values. Spaces and operators are also allowed within a valid value.
{% endhint %}
### **Validation Type 2: Regex (Pattern Matching)**
Use regular expressions to validate cell values against a pattern.
**How to set up:**
1. Open the Valid Values modal.
2. Select the **Regex** tab.
3. Enter your regular expression in the **Expression** field. Examples:
1. Email validation `^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}$`
2. Phone (US) `^\d{3}-\d{3}-\d{4}$`
3. Postal Code `^\d{5}(-\d{4})?$`
4. Alphanumeric `^[A-Za-z0-9]+$`
4. Test your regex:
* Enter a test string in the **Test String** field.
* Click **Test Regex** to verify if the pattern matches.
5. Click **Save values**.
For more information about regular expressions and pattern syntax, see:
* [MDN Web Docs](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_expressions)
* [Regex101](https://regex101.com/)
### **Validation Type 3: Lookup Table Reference**
Validate values against data from a Lookup Table in your space.
**For detailed information** about Lookup Table References and how they work, see [Lookup Table Reference](/doc/rules/lookup-table/using-lookup-tables-in-rules.md)
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