CopilotKit Debugging Skill

When to Use

Invoke this skill when:

• The CopilotKit runtime is unreachable or returning errors
• Agents fail to connect, respond, or stream events
• Frontend tools are not executing or returning results
• Transcription (voice) is failing
• Version mismatch errors appear between packages
• AG-UI SSE events are malformed or missing
• CORS errors block browser requests to the runtime

Diagnostic Workflow

Step 1: Gather Information

Before proposing any fix, collect:

1. Package versions -- Run npm ls @copilotkit/runtime @copilotkit/react @copilotkit/core @ag-ui/client (or the v1 equivalents). Version mismatches between runtime and react packages are a common root cause.
2. Runtime mode -- Is this SSE mode (CopilotSseRuntime) or Intelligence mode (CopilotIntelligenceRuntime)? Check the runtime constructor.
3. Transport configuration -- What is runtimeUrl set to in CopilotKitProvider? Does it match the basePath in createCopilotEndpoint?
4. Agent type -- Is the agent a BuiltInAgent, LangGraphAgent, A2AAgent, or custom AbstractAgent?
5. Error messages -- Collect the exact error from browser console and server logs. CopilotKit uses structured error codes (see references/error-patterns.md).
6. Browser network tab -- Check the /info request (runtime discovery), the /agent/:id/run SSE stream, and any CORS preflight failures.

Step 2: Check Logs and Error Codes

CopilotKit has three error code systems:

• V1 error codes -- Legacy error codes from the v1 runtime layer (@copilotkit/runtime). Codes like NETWORKERROR, AGENTNOTFOUND, APINOT_FOUND. Still surfaced in some contexts since @copilotkit/* packages wrap v2 internally.
• V2 CopilotKitCoreErrorCode -- Used by @copilotkit/core. Codes like runtimeinfofetchfailed, agentconnectfailed, agentrun_failed.
• TranscriptionErrorCode -- Used by both v1 and v2 for voice transcription. Codes like servicenotconfigured, ratelimited, authfailed.

Match the error code to the catalog in references/error-patterns.md for root cause and resolution.

Step 3: Trace AG-UI Events

For streaming/agent issues, trace the AG-UI event flow:

1. RunStartedEvent -- Confirms the agent run was initiated
2. TextMessageStartEvent / TextMessageChunkEvent / TextMessageEndEvent -- Text streaming
3. ToolCallStartEvent / ToolCallArgsEvent / ToolCallEndEvent -- Tool invocations
4. ToolCallResultEvent -- Tool results flowing back
5. StateSnapshotEvent / StateDeltaEvent -- Agent state synchronization
6. ReasoningStartEvent / ReasoningMessageContentEvent / ReasoningMessageEndEvent -- Reasoning tokens (can cause stalls, see issue #3323)
7. RunFinishedEvent -- Successful completion
8. RunErrorEvent -- Agent-level error

Enable the CopilotKit Web Inspector (@copilotkit/web-inspector) to see events in real time. Or check the SSE stream directly in the browser Network tab -- each event is a data: line in the text/event-stream response.

Step 4: Identify Root Cause

Use the reference documents to match symptoms to known issues:

• references/runtime-debugging.md -- Connectivity, CORS, transport, SSE streaming
• references/agent-debugging.md -- Agent discovery, state sync, tool execution, AG-UI protocol
• references/error-patterns.md -- Complete error code catalog with resolutions
• references/quick-workflows.md -- Step-by-step diagnostic sequences for common scenarios

Step 5: Fix and Verify

1. Apply the fix
2. Verify the /info endpoint returns the expected agent list
3. Confirm the SSE stream produces a complete event sequence (RunStarted through RunFinished)
4. Check the browser console for any remaining structured errors

Using mcp-docs for Live Documentation Lookups

During debugging, use the copilotkit-docs MCP server to look up the latest CopilotKit documentation. This server provides two tools: search-docs (search documentation) and search-code (search source code examples).

MCP Setup

Claude Code: The MCP server is auto-configured by the plugin's .mcp.json -- no manual setup needed. The agent can call the search-docs and search-code tools from the copilotkit-docs server directly.

Codex: Add the following to your .codex/config.toml:

[mcp_servers.copilotkit-docs]
type = "http"
url = "https://mcp.copilotkit.ai/mcp"

Tool Usage

The search-docs and search-code tools are invoked as MCP tool calls (not CLI commands). Examples of what to search for during debugging:

search-docs("AGENT_NOT_FOUND")
search-docs("CopilotRuntime configuration")
search-docs("AG-UI protocol events")
search-docs("troubleshooting common issues")
search-docs("CORS configuration copilotkit")
search-code("CopilotRuntime error handling")

The official troubleshooting docs are at:

• https://docs.copilotkit.ai/troubleshooting/common-issues
• https://docs.copilotkit.ai/coagents/troubleshooting/common-issues

Key File Locations in the CopilotKit Codebase