{"meta":{"title":"Session lifecycle hooks","intro":"Session lifecycle hooks let you respond to session start and end events. Use them to:","product":"GitHub Copilot","breadcrumbs":[{"href":"/en/copilot","title":"GitHub Copilot"},{"href":"/en/copilot/how-tos","title":"How-tos"},{"href":"/en/copilot/how-tos/copilot-sdk","title":"Copilot SDK"},{"href":"/en/copilot/how-tos/copilot-sdk/hooks","title":"Use hooks"},{"href":"/en/copilot/how-tos/copilot-sdk/hooks/session-lifecycle","title":"Session Lifecycle"}],"documentType":"article"},"body":"# Session lifecycle hooks\n\nSession lifecycle hooks let you respond to session start and end events. Use them to:\n\n\n\n\n\n* Initialize context when sessions begin\n* Clean up resources when sessions end\n* Track session metrics and analytics\n* Configure session behavior dynamically\n\n## Session start hook {#session-start}\n\nThe `onSessionStart` hook is called when a session begins (new or resumed).\n\n### Hook signature\n\n
\n
TypeScript
\n\n```typescript\ntype SessionStartHandler = (\n input: SessionStartHookInput,\n invocation: HookInvocation\n) => Promise;\n```\n\n
\n\n
Python
\n\n```python\nSessionStartHandler = Callable[\n [SessionStartHookInput, dict[str, str]],\n Awaitable[SessionStartHookOutput | None]\n]\n```\n\n
\n\n
Go
\n\n```golang\ntype SessionStartHandler func(\n input SessionStartHookInput,\n invocation HookInvocation,\n) (*SessionStartHookOutput, error)\n```\n\n
\n\n
.NET
\n\n```csharp\npublic delegate Task SessionStartHandler(\n SessionStartHookInput input,\n HookInvocation invocation);\n```\n\n
\n\n
Java
\n\n```java\n@FunctionalInterface\npublic interface SessionStartHandler {\n CompletableFuture handle(\n SessionStartHookInput input,\n HookInvocation invocation);\n}\n```\n\n
\n\n
\n\n### Input\n\n| Field | Type | Description |\n| --------------- | ------------------------------------ | ------------------------------------------ |\n| `timestamp` | number | Unix timestamp when the hook was triggered |\n| `cwd` | string | Current working directory |\n| `source` | `\"startup\"` \\| `\"resume\"` \\| `\"new\"` | How the session was started |\n| `initialPrompt` | string \\| undefined | The initial prompt if provided |\n\n### Output\n\n| Field | Type | Description |\n| ------------------- | ------ | ------------------------------- |\n| `additionalContext` | string | Context to add at session start |\n| `modifiedConfig` | object | Override session configuration |\n\n### Examples\n\n#### Add project context at start\n\n
\n
TypeScript
\n\n```typescript\nconst session = await client.createSession({\n hooks: {\n onSessionStart: async (input, invocation) => {\n console.log(`Session ${invocation.sessionId} started (${input.source})`);\n \n const projectInfo = await detectProjectType(input.cwd);\n \n return {\n additionalContext: `\nThis is a ${projectInfo.type} project.\nMain language: ${projectInfo.language}\nPackage manager: ${projectInfo.packageManager}\n `.trim(),\n };\n },\n },\n});\n```\n\n
\n\n
Python
\n\n```python\nfrom copilot.session import PermissionHandler\n\nasync def on_session_start(input_data, invocation):\n print(f\"Session {invocation['session_id']} started ({input_data['source']})\")\n \n project_info = await detect_project_type(input_data[\"cwd\"])\n \n return {\n \"additionalContext\": f\"\"\"\nThis is a {project_info['type']} project.\nMain language: {project_info['language']}\nPackage manager: {project_info['packageManager']}\n \"\"\".strip()\n }\n\nsession = await client.create_session(on_permission_request=PermissionHandler.approve_all, hooks={\"on_session_start\": on_session_start})\n```\n\n
\n\n
\n\n#### Handle session resume\n\n```typescript\nconst session = await client.createSession({\n hooks: {\n onSessionStart: async (input, invocation) => {\n if (input.source === \"resume\") {\n // Load previous session state\n const previousState = await loadSessionState(invocation.sessionId);\n \n return {\n additionalContext: `\nSession resumed. Previous context:\n- Last topic: ${previousState.lastTopic}\n- Open files: ${previousState.openFiles.join(\", \")}\n `.trim(),\n };\n }\n return null;\n },\n },\n});\n```\n\n#### Load user preferences\n\n```typescript\nconst session = await client.createSession({\n hooks: {\n onSessionStart: async () => {\n const preferences = await loadUserPreferences();\n \n const contextParts = [];\n \n if (preferences.language) {\n contextParts.push(`Preferred language: ${preferences.language}`);\n }\n if (preferences.codeStyle) {\n contextParts.push(`Code style: ${preferences.codeStyle}`);\n }\n if (preferences.verbosity === \"concise\") {\n contextParts.push(\"Keep responses brief and to the point.\");\n }\n \n return {\n additionalContext: contextParts.join(\"\\n\"),\n };\n },\n },\n});\n```\n\n## Session end hook {#session-end}\n\nThe `onSessionEnd` hook is called when a session ends.\n\n### Hook signature\n\n
\n
TypeScript
\n\n```typescript\ntype SessionEndHandler = (\n input: SessionEndHookInput,\n invocation: HookInvocation\n) => Promise;\n```\n\n
\n\n
Python
\n\n```python\nSessionEndHandler = Callable[\n [SessionEndHookInput, dict[str, str]],\n Awaitable[SessionEndHookOutput | None]\n]\n```\n\n
\n\n
Go
\n\n```golang\ntype SessionEndHandler func(\n input SessionEndHookInput,\n invocation HookInvocation,\n) (*SessionEndHookOutput, error)\n```\n\n
\n\n
.NET
\n\n```csharp\npublic delegate Task SessionEndHandler(\n SessionEndHookInput input,\n HookInvocation invocation);\n```\n\n
\n\n
Java
\n\n```java\n@FunctionalInterface\npublic interface SessionEndHandler {\n CompletableFuture handle(\n SessionEndHookInput input,\n HookInvocation invocation);\n}\n```\n\n
\n\n
\n\n### Input\n\n| Field | Type | Description |\n| -------------- | ------------------- | ------------------------------------------- |\n| `timestamp` | number | Unix timestamp when the hook was triggered |\n| `cwd` | string | Current working directory |\n| `reason` | string | Why the session ended (see below) |\n| `finalMessage` | string \\| undefined | The last message from the session |\n| `error` | string \\| undefined | Error message if session ended due to error |\n\n#### End reasons\n\n| Reason | Description |\n| ------------- | ----------------------------------- |\n| `\"complete\"` | Session completed normally |\n| `\"error\"` | Session ended due to an error |\n| `\"abort\"` | Session was aborted by user or code |\n| `\"timeout\"` | Session timed out |\n| `\"user_exit\"` | User explicitly ended the session |\n\n### Output\n\n| Field | Type | Description |\n| ---------------- | --------- | -------------------------------------------- |\n| `suppressOutput` | boolean | Suppress the final session output |\n| `cleanupActions` | string\\[] | List of cleanup actions to perform |\n| `sessionSummary` | string | Summary of the session for logging/analytics |\n\n### Examples\n\n#### Track session metrics\n\n
\n
TypeScript
\n\n```typescript\nconst sessionStartTimes = new Map();\n\nconst session = await client.createSession({\n hooks: {\n onSessionStart: async (input, invocation) => {\n sessionStartTimes.set(invocation.sessionId, input.timestamp);\n return null;\n },\n onSessionEnd: async (input, invocation) => {\n const startTime = sessionStartTimes.get(invocation.sessionId);\n const duration = startTime ? input.timestamp - startTime : 0;\n \n await recordMetrics({\n sessionId: invocation.sessionId,\n duration,\n endReason: input.reason,\n });\n \n sessionStartTimes.delete(invocation.sessionId);\n return null;\n },\n },\n});\n```\n\n
\n\n
Python
\n\n```python\nfrom copilot.session import PermissionHandler\n\nsession_start_times = {}\n\nasync def on_session_start(input_data, invocation):\n session_start_times[invocation[\"session_id\"]] = input_data[\"timestamp\"]\n return None\n\nasync def on_session_end(input_data, invocation):\n start_time = session_start_times.get(invocation[\"session_id\"])\n duration = input_data[\"timestamp\"] - start_time if start_time else 0\n \n await record_metrics({\n \"session_id\": invocation[\"session_id\"],\n \"duration\": duration,\n \"end_reason\": input_data[\"reason\"],\n })\n \n session_start_times.pop(invocation[\"session_id\"], None)\n return None\n\nsession = await client.create_session(on_permission_request=PermissionHandler.approve_all, hooks={\n \"on_session_start\": on_session_start,\n \"on_session_end\": on_session_end,\n })\n```\n\n
\n\n
\n\n#### Clean up resources\n\n```typescript\nconst sessionResources = new Map();\n\nconst session = await client.createSession({\n hooks: {\n onSessionStart: async (input, invocation) => {\n sessionResources.set(invocation.sessionId, { tempFiles: [] });\n return null;\n },\n onSessionEnd: async (input, invocation) => {\n const resources = sessionResources.get(invocation.sessionId);\n \n if (resources) {\n // Clean up temp files\n for (const file of resources.tempFiles) {\n await fs.unlink(file).catch(() => {});\n }\n sessionResources.delete(invocation.sessionId);\n }\n \n console.log(`Session ${invocation.sessionId} ended: ${input.reason}`);\n return null;\n },\n },\n});\n```\n\n#### Save session state for resume\n\n```typescript\nconst session = await client.createSession({\n hooks: {\n onSessionEnd: async (input, invocation) => {\n if (input.reason !== \"error\") {\n // Save state for potential resume\n await saveSessionState(invocation.sessionId, {\n endTime: input.timestamp,\n cwd: input.cwd,\n reason: input.reason,\n });\n }\n return null;\n },\n },\n});\n```\n\n#### Log session summary\n\n```typescript\nconst sessionData: Record = {};\n\nconst session = await client.createSession({\n hooks: {\n onSessionStart: async (input, invocation) => {\n sessionData[invocation.sessionId] = { \n prompts: 0, \n tools: 0, \n startTime: input.timestamp \n };\n return null;\n },\n onUserPromptSubmitted: async (_, invocation) => {\n sessionData[invocation.sessionId].prompts++;\n return null;\n },\n onPreToolUse: async (_, invocation) => {\n sessionData[invocation.sessionId].tools++;\n return { permissionDecision: \"allow\" };\n },\n onSessionEnd: async (input, invocation) => {\n const data = sessionData[invocation.sessionId];\n console.log(`\nSession Summary:\n ID: ${invocation.sessionId}\n Duration: ${(input.timestamp - data.startTime) / 1000}s\n Prompts: ${data.prompts}\n Tool calls: ${data.tools}\n End reason: ${input.reason}\n `.trim());\n \n delete sessionData[invocation.sessionId];\n return null;\n },\n },\n});\n```\n\n## Agent stop hook {#agent-stop}\n\nThe agent stop hook runs when the top-level agent naturally reaches the end of a turn. It is separate from `onSessionEnd`: the session remains active, and the hook can request another agent turn.\n\n| Language | Handler |\n| -------------------- | ---------------- |\n| Node.js / TypeScript | `onAgentStop` |\n| Python | `on_agent_stop` |\n| Go | `OnAgentStop` |\n| .NET | `OnAgentStop` |\n| Rust | `on_agent_stop` |\n| Java | `setOnAgentStop` |\n\n### Input\n\nThe public member names follow each language's casing conventions:\n\n| Meaning | Node.js / Python | Go / .NET | Rust | Java |\n| ------------------------------------------------------------------ | ---------------- | ---------------- | ------------------ | --------------------- |\n| Why the agent stopped, such as `end_turn` | `stopReason` | `StopReason` | `stop_reason` | `getStopReason()` |\n| Path to the on-disk session transcript | `transcriptPath` | `TranscriptPath` | `transcript_path` | `getTranscriptPath()` |\n| Whether an earlier block decision already forced this continuation | `stopHookActive` | `StopHookActive` | `stop_hook_active` | `getStopHookActive()` |\n\n### Output\n\nReturn no output to let the agent stop. Return a block decision to enqueue another user message and continue:\n\n```json\n{\n \"decision\": \"block\",\n \"reason\": \"Run the final validation and fix any failures.\"\n}\n```\n\nUse the active-stop member listed above to avoid repeatedly blocking an agent that has already continued because of this hook. The runtime also caps consecutive block decisions.\n\n## Best practices\n\n1. **Keep `onSessionStart` fast** - Users are waiting for the session to be ready.\n\n2. **Handle all end reasons** - Don't assume sessions end cleanly; handle errors and aborts.\n\n3. **Clean up resources** - Use `onSessionEnd` to free any resources allocated during the session.\n\n4. **Store minimal state** - If tracking session data, keep it lightweight.\n\n5. **Make cleanup idempotent** - `onSessionEnd` might not be called if the process crashes.\n\n## See also\n\n* [Use hooks](/en/copilot/how-tos/copilot-sdk/hooks)\n* [Error handling hook](/en/copilot/how-tos/copilot-sdk/hooks/error-handling)\n* [Debugging guide](/en/copilot/how-tos/copilot-sdk/troubleshooting/debugging)"}