> For the complete documentation index, see [llms.txt](https://docs.abtasty.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.abtasty.com/feature-experimentation-and-rollout/campaign-creation/how-to-create-server-side-a-b-tests/variations.md).
# Variations
The **Variations** step is the core of your A/B test server-side campaign.
This is where you define what is actually being tested by configuring **flags and their values**.
Each variation represents a different experience exposed to users.
### What is a variation?
In Feature Experimentation and Rollout (FE\&R), a variation is defined by one or multiple **flag values**.
When a user is assigned to a variation, the SDK or Decision API returns the corresponding flag configuration.
This allows your backend to control exactly what experience is delivered.
### Configuring a Variation
You can manage your variations directly from the interface:
* Add a new variation
* Duplicate an existing variation
* Delete a variation
* Add multiple flags within a variation
For each variation, you must define:
* A **flag key**
* A **type**
* A **value**
Example:
* Flag: `button_color`
* Type: `String`
* Value: `orange`
#### Configuration modes
You can configure your variations using two modes:
**Standard mode**
This is the default and most commonly used mode.
It allows you to:
* Select a flag
* Define its type
* Assign a value
This mode is ideal for most use cases and provides a clear and structured interface.
**Expert mode (JSON)**
Expert mode allows you to define your variation using JSON.
This is useful when:
* Working with complex configurations
* Passing structured objects
* Managing multiple parameters at once
### Best practices
* Keep variations simple and focused on a single hypothesis
* Avoid testing too many changes in one variation
* Use clear naming for each variation (e.g. “Control”, “New CTA”, “Variant B”)
* Ensure flag values are correctly handled in your backend logic
{% hint style="info" %}
#### **Original vs Variation**
Every campaign includes an **Original** variation. You have two options:
* **Override the original (recommended):** Define a flag and value directly in FE\&R.\
It a*voids relying on hardcoded fallback values and keeps configuration centralized in the platform.*
* **Use fallback values in your code:** Do not configure the original in FE\&R and rely on codebase defaults.\
It m*ay result in less visibility and harder-to-maintain logic.*
{% endhint %}
#### Next step
Once your variations are configured, proceed to [Goals](/feature-experimentation-and-rollout/campaign-creation/how-to-create-server-side-a-b-tests/goals.md)
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