# Entropy
<a name="dqdl-rule-types-Entropy"></a>

Checks whether the *entropy* value of a column matches a given expression. Entropy measures the level of information that's contained in a message. Given the probability distribution over values in a column, entropy describes how many bits are required to identify a value.

**Syntax**

```
Entropy <COL_NAME> <EXPRESSION>
```
+ **COL\$1NAME** – The name of the column that you want to evaluate the data quality rule against.

  **Supported column types**: Any column type
+ **EXPRESSION** – An expression to run against the rule type response in order to produce a Boolean value. For more information, see [Expressions](dqdl.md#dqdl-syntax-rule-expressions).

**Example: Column entropy**

The following example rule checks that the column named `Feedback` has an entropy value greater than one.

```
Entropy "Star_Rating" > 1
Entropy "First_Name" > 1  where "Customer_ID < 10"
```

 **Sample dynamic rules** 
+ `Entropy "colA" < max(last(10))`
+ `Entropy "colA" between min(last(10)) and max(last(10))`