copilotkit-debug

First verify the agent is registered by querying the /info endpoint, then inspect the SSE stream from the /agent/:id/run request in the browser Network tab. A stream with only RunStartedEvent usually indicates a missing LLM API key or a stalled tool call.

A 404 means the basePath in createCopilotEndpoint does not match the runtimeUrl in CopilotKitProvider, or the runtime server is not mounted at that path. Connection refused means the server is not running on the expected host and port.

The runtime allows all origins without credentials by default. If you need cookies, set an explicit origin with credentials: true in createCopilotEndpoint and pass credentials="include" to CopilotKitProvider, since wildcard origins cannot be used with credentials.

Check that useFrontendTool is registered with the exact case-sensitive tool name before the agent run starts. Inspect the SSE stream for ToolCallStartEvent; if ToolCallResultEvent never appears, the execute handler likely threw or the component is not mounted.

VERSION_MISMATCH occurs when @copilotkit/* packages are on different versions. Run npm ls @copilotkit/runtime @copilotkit/react @copilotkit/core and align all packages to the same version.

Reasoning events (REASONING_*) can cause permanent stalls if the client event handler does not consume them properly, a known issue tracked as GitHub issue #3323. Updating to a version with reasoning event handling fixes resolves it.