Stream session events with the Devin SDK

Every event is a member of one discriminated union, SessionEvent, so a switch on event.type narrows it. Tool calls carry a normalized detail that says which tool it is and what it was given, the same for local and cloud sessions:

for await (const event of session.run("Explain three uses for a coding agent SDK")) {
  switch (event.type) {
    case "message_delta":
      process.stdout.write(event.text);
      break;
    case "thought_delta":
      break; // Devin's reasoning, if you want to show it
    case "tool_call": {
      const { detail, status } = event.call;
      if (detail.tool === "exec") console.log(`$ ${detail.command ?? ""}`, status, detail.exitCode);
      if (detail.tool === "edit") console.log("edited", detail.path);
      if (detail.tool === "mcp") console.log("mcp", detail.server, detail.name);
      break;
    }
    case "plan":
      console.log(event.entries.filter((e) => e.status !== "completed"));
      break;
  }
}

Tool calls, the same on both agents

The local CLI and the cloud describe tools differently on the wire (typed rawInput and cognition.ai/inferenceToolName locally; cognition.ai/eventType plus _meta details such as cognition.ai/command and cognition.ai/fileUpdates on the cloud). ToolCall.detail normalizes both into one discriminated union — exec, read, write, edit, list_directory, file_search, mcp, permission_request, ask_user_question, computer_use, report_blocker, or other — so consumers narrow on detail.tool and never see the difference. computer_use (added in 0.0.1-beta.2) is Devin driving its browser or desktop on the cloud; detail.actions lists the typed actions it took (key, type, screenshot, …). The raw rawInput, meta, toolName and inferenceToolName stay on the call for anything the union does not cover.

Cognition extension notifications

Cognition-specific events (_cognition.ai/* notifications — agent stop causes, context compaction, connection retries, …) are surfaced as a typed union via session.onExtension:

import { CognitionExtensionMethod, isExtension } from "@cognition-ai/sdk";

session.onExtension = (notification) => {
  if (isExtension(notification, CognitionExtensionMethod.AgentStopped)) {
    console.log(notification.cause, notification.stats);
  }
};

The same event stream is what you get from a session you did not start; see Watch a session. The quickstart example switches over every event type in one file.

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Stream session events with the Devin SDK

Tool calls, the same on both agents

Cognition extension notifications

​Tool calls, the same on both agents

​Cognition extension notifications

Tool calls, the same on both agents

Cognition extension notifications