copilotkit-agui

Extend AbstractAgent and implement run() to return an RxJS Observable of events, or create an HTTP endpoint that accepts RunAgentInput and writes SSE-encoded events using EventEncoder from @ag-ui/encoder. Always emit RUN_STARTED first and RUN_FINISHED or RUN_ERROR last.

Emit RUN_STARTED first, then TEXT_MESSAGE_START, one or more TEXT_MESSAGE_CONTENT events with non-empty deltas, TEXT_MESSAGE_END, and finally RUN_FINISHED. Alternatively, use TEXT_MESSAGE_CHUNK events which the client auto-expands into the full triad.

The agent emits TOOL_CALL_START, TOOL_CALL_ARGS, and TOOL_CALL_END linked by toolCallId, then typically ends the run. The client executes the tool, adds the result as a tool-role message, and starts a new run where the agent reads the result from input.messages.

STATE_SNAPSHOT replaces the entire client-side state with a complete object. STATE_DELTA applies incremental updates as RFC 6902 JSON Patch operations against existing state, which is more efficient for frequent small changes.

Common causes include missing SSE headers (Content-Type: text/event-stream), malformed data lines that fail Zod schema parsing, incorrect event ordering, or empty delta strings. Verify the wire format matches 'data: {JSON}\n\n' and events pass the client's verifyEvents check.

Do not implement AG-UI manually when working with CopilotKit React hooks, runtime setup, or existing framework integrations like LangGraph, Mastra, or CrewAI, since those already handle the protocol. Use it only for custom backends or new framework integrations.