> ## Documentation Index
> Fetch the complete documentation index at: https://docs.purpify.host/llms.txt
> Use this file to discover all available pages before exploring further.

# Troubleshoot Java plugin errors

> Fix missing dependencies, incompatible Java plugins, invalid configuration, and plugin startup failures on Purpify.

Start with the first error that names the plugin. Most plugin failures come from unsupported server software, a missing dependency, an incompatible Minecraft or Java version, or an invalid configuration.

## Identify the failure

Open the [console](/panel/console) during startup and compare the message with these common causes:

| Console message or symptom                         | Likely cause                                                          | Next check                                                                   |
| -------------------------------------------------- | --------------------------------------------------------------------- | ---------------------------------------------------------------------------- |
| `UnknownDependencyException` or unknown dependency | A required plugin is missing                                          | Install the dependency and a version compatible with the server.             |
| `InvalidPluginException`                           | Wrong file, damaged download, or incompatible plugin build            | Download the correct server plugin from its official source.                 |
| `UnsupportedClassVersionError`                     | The plugin requires a newer Java runtime                              | Check the plugin requirements and selected Minecraft server version.         |
| `NoClassDefFoundError`                             | Missing dependency or incompatible API                                | Find the first plugin named before the stack trace repeats.                  |
| Plugin is ignored or does not appear               | Server software does not support it, or the file is not in `/plugins` | Confirm the server uses compatible plugin software and the file is a `.jar`. |
| Configuration parsing error                        | Invalid YAML, JSON, or another config format                          | Restore the last working config and reapply one change.                      |

## Fix one plugin at a time

<Steps>
  <Step title="Stop the server">
    Leave the server stopped while changing plugin files.
  </Step>

  <Step title="Create a backup">
    Back up the server and download the plugin configuration when it contains important data.
  </Step>

  <Step title="Verify compatibility">
    Confirm the plugin supports the Minecraft version, server software, and Java runtime used by the server. Install every dependency listed by the author.
  </Step>

  <Step title="Replace or isolate the file">
    Replace an invalid `.jar` with the correct release. To test removal, move the suspected plugin outside `/plugins` rather than deleting its data folder.
  </Step>

  <Step title="Start once and read the result">
    Watch the complete startup. If another error appears, diagnose that new first error before changing more plugins.
  </Step>
</Steps>

<Warning>
  Avoid `/reload` when diagnosing plugins. Restart the server so plugins load through a clean startup sequence.
</Warning>

For installation steps, see [Install Java plugins](/java/plugins).