# Experience As well as player, pets can also gain experience and level up. In each level they can get special [abilities](/skills.md) like [Backpack](/skills/backpack.md). There are two different ways the experience is converted into levels, etc at the moment. ## Default `Default` is the default way the experience part is calculated. When `MyPet.LevelSystem.CalculationMode` is set to `default` all pets will level up like normal players would level up like in [Minecraft Pre-Snapshot 12w23a](https://minecraft.gamepedia.com/Experience#Values_of_Beta_1.8_-_Before_1.3.1_.2812w23a.29). ## [JavaScript](/systems/experience/expjs.md) This is the advanced way where you can create your own level behavior. When `MyPet.LevelSystem.CalculationMode` is set to `JS` or `JavaScript` the plugin uses the `exp.js` in the *MyPet*-folder to calculate the required experience to levelup. In order to use this feature the plugin needs the [rhino.jar](https://github.com/mozilla/rhino/releases) inside the *MyPet* folder. You can find an example [here](/systems/experience/expjs.md#example) and a further discription [here](/systems/experience/expjs.md). If you have any questions related to this topic please send me a message on [Discord ](http://discord.mypet-plugin.de)in the help channel. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://wiki.mypet-plugin.de/systems/experience.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.