> For the complete documentation index, see [llms.txt](https://docs.rulecube.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.rulecube.com/v2.5/how-to-guides/ruleset-development/create-a-rule.md).
# Create a Rule
## Introduction
This guide explains how to create rules for a ruleset.
**Rules** are the main engine of rulesets and the logical implementation of a business rule. For example, suppose you implement a business rule for determining the maximum loan amount given a certain income as input. In that case, the rule is the implementation of the business rule that calculates the actual maximum loan amount:
Input
Rule
Output
Income
Calculate maximum loan amount
Maximum loan amount
{% hint style="info" %}
To distinguish rules at the entity and ruleset level, Rulecube speaks of **entity rules** and **global rules**. This guide is about global rules.
{% endhint %}
### The result of rules as output
In general, a rule performs a calculation or makes a decision and returns the result as the output of the ruleset. To facilitate different (business) rule scenarios, Rulecube supports different output types, such as `string` and `date`. For instance, the aforementioned maximum loan amount output is of the `number` type.
List of output types and additional rule/output settings
**Output types**
* `any`\
As its name implies, an `any` input can contain any type of input.
* `number`\
This type includes negative values and numbers with decimals.
* `boolean`\
This type expects the values `true` or `false`.
* `string`\
This type can contain any text, including numbers.
* `date`\
This type expects a date in `mm/dd/yyyy` format.
* `enum`\
For this type, you can set a list of possible values. For example, `good`, `bad`, `ok`.
* `array`\
This type contains a one-dimensional array of values.
**Additional rule/output settings**
* If you select this type, Rulecube adds the **Possible values** field to the **Rule details** page, where you can enter the corresponding values.
* If you select this type, Rulecube adds the **Sub type** field to the **Rule details** page, where you can set the type for the array elements.
## Procedure
Let's walk through the steps for creating a rule that calculates the maximum loan amount as 25 percent of a person's annual income.
1. Create a ruleset named `MaxLoan`.
2. Create an input named `AnnualIncome` with **Type** = `number` and **Label** = `The annual income`.
3. Create a constant named `LoanPercentage` with **Type** = `simple` and **Value** = `25`.
4. Click the **+** sign behind **Rules** from the left menu.\
↳ The **Rule details** page opens.
5. In the **Name** field, enter the name for the rule. For example, `LoanCalculation`.
6. In the **Output name** field, enter `MaximumLoanAmount`.
7. In the **Type** list, select **number**.
8. In the **Expression** field, enter the following code to calculate the maximum loan amount:
```javascript
AnnualIncome * (LoanPercentage / 100)
```
9. Click **Save**.
10. Try the ruleset out.
#### Revert changes to an expression
As an extra, let's look at the **Revert** feature for changes to expressions in Rulecube:
9. Move back to the rule again.
10. Change the code for the **Expression** to:
```javascript
AnnualIncome * LoanPercentage / 100
```
Now, let's assume you are unsatisfied with this change and want the previous code back. You could retype the original code if you remember, but Rulecube enables you to revert the changes much easier:
11. Click above the expression.\
↳ Rulecube reverts your changes and shows your original code again.
12. Press `Ctrl+S` to save your work.
## Additional resources
* How-to Guide: [Try Out a Rule](/v2.5/how-to-guides/ruleset-development/try-out-a-ruleset.md).
* How-to Guide: [Call a Rule from Your Software](/v2.5/how-to-guides/ruleset-development/call-a-ruleset-from-your-software.md).
---
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