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claude-code - 💡(How to fix) Fix [BUG] JetBrains plugin 0.1.14-beta: NoClassDefFoundError io.ktor.server.cio.CIO on startup (IDEA build 253.31033.145)

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Error Message

Stack trace com.intellij.diagnostic.PluginException: io/ktor/server/cio/CIO [Plugin: com.anthropic.code.plugin] at com.intellij.ide.startup.impl.StartupManagerImplKt$launchActivity$1.invokeSuspend(StartupManagerImpl.kt:517) at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:34) at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:100) at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:610) at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runDefaultDispatcherTask(CoroutineScheduler.kt:1194) at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:906) at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:775) at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:762) Caused by: java.lang.NoClassDefFoundError: io/ktor/server/cio/CIO at com.anthropic.code.plugin.services.MCPService.start(MCPService.kt:57) at com.anthropic.code.plugin.startup.PostStartupActivity.execute(PostStartupActivity.kt:14) at com.intellij.ide.startup.impl.StartupManagerImplKt$launchActivity$1.invokeSuspend(StartupManagerImpl.kt:511) ... 7 more Caused by: java.lang.ClassNotFoundException: io.ktor.server.cio.CIO PluginClassLoader(plugin=PluginMainDescriptor(name=Claude Code [Beta], id=com.anthropic.code.plugin, version=0.1.14-beta, isBundled=false, path=~\AppData\Roaming\JetBrains\IntelliJIdea2025.3\plugins\claude-code-jetbrains-plugin-0.1.14-beta.jar), packagePrefix=null, state=active, parents=...) at com.intellij.ide.plugins.cl.PluginClassLoader.loadClass(PluginClassLoader.kt:149) at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:526) ... 10 more

(Full 'PluginClassLoader' parent chain trimmed for brevity; it lists the standard 2025.3 platform Terminal and IDEA CORE content module descriptors. Happy to provide the full untrimmed trace on request.)

Root Cause

Stack trace
`
com.intellij.diagnostic.PluginException: io/ktor/server/cio/CIO [Plugin: com.anthropic.code.plugin]
	at com.intellij.ide.startup.impl.StartupManagerImplKt$launchActivity$1.invokeSuspend(StartupManagerImpl.kt:517)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:34)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:100)
	at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:610)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runDefaultDispatcherTask(CoroutineScheduler.kt:1194)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:906)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:775)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:762)
Caused by: java.lang.NoClassDefFoundError: io/ktor/server/cio/CIO
	at com.anthropic.code.plugin.services.MCPService.start(MCPService.kt:57)
	at com.anthropic.code.plugin.startup.PostStartupActivity.execute(PostStartupActivity.kt:14)
	at com.intellij.ide.startup.impl.StartupManagerImplKt$launchActivity$1.invokeSuspend(StartupManagerImpl.kt:511)
	... 7 more
Caused by: java.lang.ClassNotFoundException: io.ktor.server.cio.CIO PluginClassLoader(plugin=PluginMainDescriptor(name=Claude Code [Beta], id=com.anthropic.code.plugin, version=0.1.14-beta, isBundled=false, path=~\AppData\Roaming\JetBrains\IntelliJIdea2025.3\plugins\claude-code-jetbrains-plugin-0.1.14-beta.jar), packagePrefix=null, state=active, parents=...)
	at com.intellij.ide.plugins.cl.PluginClassLoader.loadClass(PluginClassLoader.kt:149)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:526)
	... 10 more
`

Fix Action

Fix / Workaround

Stack trace
`
com.intellij.diagnostic.PluginException: io/ktor/server/cio/CIO [Plugin: com.anthropic.code.plugin]
	at com.intellij.ide.startup.impl.StartupManagerImplKt$launchActivity$1.invokeSuspend(StartupManagerImpl.kt:517)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:34)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:100)
	at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:610)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runDefaultDispatcherTask(CoroutineScheduler.kt:1194)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:906)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:775)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:762)
Caused by: java.lang.NoClassDefFoundError: io/ktor/server/cio/CIO
	at com.anthropic.code.plugin.services.MCPService.start(MCPService.kt:57)
	at com.anthropic.code.plugin.startup.PostStartupActivity.execute(PostStartupActivity.kt:14)
	at com.intellij.ide.startup.impl.StartupManagerImplKt$launchActivity$1.invokeSuspend(StartupManagerImpl.kt:511)
	... 7 more
Caused by: java.lang.ClassNotFoundException: io.ktor.server.cio.CIO PluginClassLoader(plugin=PluginMainDescriptor(name=Claude Code [Beta], id=com.anthropic.code.plugin, version=0.1.14-beta, isBundled=false, path=~\AppData\Roaming\JetBrains\IntelliJIdea2025.3\plugins\claude-code-jetbrains-plugin-0.1.14-beta.jar), packagePrefix=null, state=active, parents=...)
	at com.intellij.ide.plugins.cl.PluginClassLoader.loadClass(PluginClassLoader.kt:149)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:526)
	... 10 more
`

Code Example

Stack trace
`
com.intellij.diagnostic.PluginException: io/ktor/server/cio/CIO [Plugin: com.anthropic.code.plugin]
	at com.intellij.ide.startup.impl.StartupManagerImplKt$launchActivity$1.invokeSuspend(StartupManagerImpl.kt:517)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:34)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:100)
	at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:610)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runDefaultDispatcherTask(CoroutineScheduler.kt:1194)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:906)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:775)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:762)
Caused by: java.lang.NoClassDefFoundError: io/ktor/server/cio/CIO
	at com.anthropic.code.plugin.services.MCPService.start(MCPService.kt:57)
	at com.anthropic.code.plugin.startup.PostStartupActivity.execute(PostStartupActivity.kt:14)
	at com.intellij.ide.startup.impl.StartupManagerImplKt$launchActivity$1.invokeSuspend(StartupManagerImpl.kt:511)
	... 7 more
Caused by: java.lang.ClassNotFoundException: io.ktor.server.cio.CIO PluginClassLoader(plugin=PluginMainDescriptor(name=Claude Code [Beta], id=com.anthropic.code.plugin, version=0.1.14-beta, isBundled=false, path=~\AppData\Roaming\JetBrains\IntelliJIdea2025.3\plugins\claude-code-jetbrains-plugin-0.1.14-beta.jar), packagePrefix=null, state=active, parents=...)
	at com.intellij.ide.plugins.cl.PluginClassLoader.loadClass(PluginClassLoader.kt:149)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:526)
	... 10 more
`

(Full 'PluginClassLoader' parent chain trimmed for brevity; it lists the standard 2025.3 platform Terminal and IDEA CORE content module descriptors. Happy to provide the full untrimmed trace on request.)
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Preflight Checklist

  • I have searched existing issues and this hasn't been reported yet
  • This is a single bug report (please file separate reports for different bugs)
  • I am using the latest version of Claude Code

What's Wrong?

Environment

  • Plugin: Claude Code [Beta] 0.1.14-beta (com.anthropic.code.plugin)
  • IDE build: 253.31033.145 (IntelliJ IDEA 2025.3 line)
  • IDE install path reports IntelliJ IDEA 2025.1.1.1 while the build is 253.x, which may be relevant
  • OS: Windows
  • Installed from: JetBrains Marketplace

Symptom The plugin throws 'PluginException' on every project open. 'MCPService.start' fails with 'NoClassDefFoundError: io/ktor/server/cio/CIO'.
The plugin class loader cannot resolve 'io.ktor.server.cio.CIO'. I've checked JetBrains Marketplace to see if there is a latest version available, but it seems there is only the 0.1.14-beta version that is available. So, no latest update that I can install from withing the IDE.

What Should Happen?

The plugin should load cleanly on IDEA build 253.x, or Anthropic publishes a 0.1.15+ build to the Marketplace that includes the ktor-server-cio runtime dependency.

Error Messages/Logs

Stack trace
`
com.intellij.diagnostic.PluginException: io/ktor/server/cio/CIO [Plugin: com.anthropic.code.plugin]
	at com.intellij.ide.startup.impl.StartupManagerImplKt$launchActivity$1.invokeSuspend(StartupManagerImpl.kt:517)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:34)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:100)
	at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:610)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runDefaultDispatcherTask(CoroutineScheduler.kt:1194)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:906)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:775)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:762)
Caused by: java.lang.NoClassDefFoundError: io/ktor/server/cio/CIO
	at com.anthropic.code.plugin.services.MCPService.start(MCPService.kt:57)
	at com.anthropic.code.plugin.startup.PostStartupActivity.execute(PostStartupActivity.kt:14)
	at com.intellij.ide.startup.impl.StartupManagerImplKt$launchActivity$1.invokeSuspend(StartupManagerImpl.kt:511)
	... 7 more
Caused by: java.lang.ClassNotFoundException: io.ktor.server.cio.CIO PluginClassLoader(plugin=PluginMainDescriptor(name=Claude Code [Beta], id=com.anthropic.code.plugin, version=0.1.14-beta, isBundled=false, path=~\AppData\Roaming\JetBrains\IntelliJIdea2025.3\plugins\claude-code-jetbrains-plugin-0.1.14-beta.jar), packagePrefix=null, state=active, parents=...)
	at com.intellij.ide.plugins.cl.PluginClassLoader.loadClass(PluginClassLoader.kt:149)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:526)
	... 10 more
`

(Full 'PluginClassLoader' parent chain trimmed for brevity; it lists the standard 2025.3 platform Terminal and IDEA CORE content module descriptors. Happy to provide the full untrimmed trace on request.)

Steps to Reproduce

  1. Install Claude Code [Beta] 0.1.14-beta from the JetBrains Marketplace into IntelliJ build 253.31033.145 (2025.3 line) on Windows.
  2. Restart the IDE
  3. Open any project (issue reproduces on every project, new or existing)
  4. Observe the Plugin Exception in the IDE Event Log / idea.log during post-startup activity. The Claude Code tool window does not initialize.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

No response

Claude Code Version

Install Claude Code [Beta] 0.1.14-beta

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

IntelliJ IDEA terminal

Additional Information

This issue is similar to the locked issue #15594

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