Hooks

Use lifecycle hooks to observe, log, and customize agent execution.

A ready-to-run example is available here!

Overview

Hooks let you observe and customize key lifecycle moments in the SDK without forking core code. Typical uses include:

• Logging and analytics
• Emitting custom metrics
• Auditing or compliance
• Tracing and debugging

Hook Types

Hook	When it runs	Can block?
PreToolUse	Before tool execution	Yes (exit 2)
PostToolUse	After tool execution	No
UserPromptSubmit	Before processing user message	Yes (exit 2)
Stop	When agent tries to finish	Yes (exit 2)
SessionStart	When conversation starts	No
SessionEnd	When conversation ends	No

Exit Codes

Hook scripts signal their result through their exit code. The SDK matches the Claude Code hook contract:

• 0 — success. The operation proceeds. stdout is parsed as JSON for structured output (decision, reason, additionalContext, continue).
• 2 — block. The operation is denied. For PreToolUse and UserPromptSubmit this rejects the action; for Stop it prevents the agent from finishing and the conversation continues. stderr / reason is surfaced as feedback.
• Any other non-zero exit code — non-blocking error. success is set to False and the error is logged via HookExecutionEvent, but the operation still proceeds.

Only exit code 2 blocks. Exit code 1 (the conventional Unix failure code) is treated as a non-blocking error. A hook intended to enforce a policy must exit with 2.

Key Concepts

• Registration points: subscribe to events or attach pre/post hooks around LLM calls and tool execution
• Isolation: hooks run outside the agent loop logic, avoiding core modifications
• Composition: enable or disable hooks per environment (local vs. prod)

Ready-to-run Example

This example is available on GitHub: examples/01_standalone_sdk/33_hooks

examples/01_standalone_sdk/33_hooks/main.py

"""OpenHands Agent SDK — Hooks Example

Demonstrates the OpenHands hooks system.
Hooks are shell scripts that run at key lifecycle events:

- PreToolUse: Block dangerous commands before execution
- PostToolUse: Log tool usage after execution
- UserPromptSubmit: Inject context into user messages
- Stop: Enforce task completion criteria

The hook scripts are in the scripts/ directory alongside this file.
"""

import os
import signal
import tempfile
from pathlib import Path

from pydantic import SecretStr

from openhands.sdk import LLM, Conversation
from openhands.sdk.hooks import HookConfig, HookDefinition, HookMatcher
from openhands.tools.preset.default import get_default_agent


signal.signal(signal.SIGINT, lambda *_: (_ for _ in ()).throw(KeyboardInterrupt()))

SCRIPT_DIR = Path(__file__).parent / "hook_scripts"

# Configure LLM
api_key = os.getenv("LLM_API_KEY")
assert api_key is not None, "LLM_API_KEY environment variable is not set."
model = os.getenv("LLM_MODEL", "anthropic/claude-sonnet-4-5-20250929")
base_url = os.getenv("LLM_BASE_URL")

llm = LLM(
    usage_id="agent",
    model=model,
    base_url=base_url,
    api_key=SecretStr(api_key),
)

# Create temporary workspace with git repo
with tempfile.TemporaryDirectory() as tmpdir:
    workspace = Path(tmpdir)
    os.system(f"cd {workspace} && git init -q && echo 'test' > file.txt")

    log_file = workspace / "tool_usage.log"
    summary_file = workspace / "summary.txt"

    # Configure hooks using the typed approach (recommended)
    # This provides better type safety and IDE support
    hook_config = HookConfig(
        pre_tool_use=[
            HookMatcher(
                matcher="terminal",
                hooks=[
                    HookDefinition(
                        command=str(SCRIPT_DIR / "block_dangerous.sh"),
                        timeout=10,
                    )
                ],
            )
        ],
        post_tool_use=[
            HookMatcher(
                matcher="*",
                hooks=[
                    HookDefinition(
                        command=(f"LOG_FILE={log_file} {SCRIPT_DIR / 'log_tools.sh'}"),
                        timeout=5,
                    )
                ],
            )
        ],
        user_prompt_submit=[
            HookMatcher(
                hooks=[
                    HookDefinition(
                        command=str(SCRIPT_DIR / "inject_git_context.sh"),
                    )
                ],
            )
        ],
        stop=[
            HookMatcher(
                hooks=[
                    HookDefinition(
                        command=(
                            f"SUMMARY_FILE={summary_file} "
                            f"{SCRIPT_DIR / 'require_summary.sh'}"
                        ),
                    )
                ],
            )
        ],
    )

    # Alternative: You can also use .from_dict() for loading from JSON config files
    # Example with a single hook matcher:
    # hook_config = HookConfig.from_dict({
    #     "hooks": {
    #         "PreToolUse": [{
    #             "matcher": "terminal",
    #             "hooks": [{"command": "path/to/script.sh", "timeout": 10}]
    #         }]
    #     }
    # })

    agent = get_default_agent(llm=llm)
    conversation = Conversation(
        agent=agent,
        workspace=str(workspace),
        hook_config=hook_config,
    )

    # Demo 1: Safe command (PostToolUse logs it)
    print("=" * 60)
    print("Demo 1: Safe command - logged by PostToolUse")
    print("=" * 60)
    conversation.send_message("Run: echo 'Hello from hooks!'")
    conversation.run()

    if log_file.exists():
        print(f"\n[Log: {log_file.read_text().strip()}]")

    # Demo 2: Dangerous command (PreToolUse blocks it)
    print("\n" + "=" * 60)
    print("Demo 2: Dangerous command - blocked by PreToolUse")
    print("=" * 60)
    conversation.send_message("Run: rm -rf /tmp/test")
    conversation.run()

    # Demo 3: Context injection + Stop hook enforcement
    print("\n" + "=" * 60)
    print("Demo 3: Context injection + Stop hook")
    print("=" * 60)
    print("UserPromptSubmit injects git status; Stop requires summary.txt\n")
    conversation.send_message(
        "Check what files have changes, then create summary.txt describing the repo."
    )
    conversation.run()

    if summary_file.exists():
        print(f"\n[summary.txt: {summary_file.read_text()[:80]}...]")

    print("\n" + "=" * 60)
    print("Example Complete!")
    print("=" * 60)

    cost = conversation.conversation_stats.get_combined_metrics().accumulated_cost
    print(f"\nEXAMPLE_COST: {cost}")

You can run the example code as-is.

The model name should follow the LiteLLM convention: provider/model_name (e.g., anthropic/claude-sonnet-4-5-20250929, openai/gpt-4o). The LLM_API_KEY should be the API key for your chosen provider.

ChatGPT Plus/Pro subscribers: You can use LLM.subscription_login() to authenticate with your ChatGPT account and access Codex models without consuming API credits. See the LLM Subscriptions guide for details.

Hook Scripts

The example uses external hook scripts in the hook_scripts/ directory:

block_dangerous.sh - PreToolUse hook

#!/bin/bash
# PreToolUse hook: Block dangerous rm -rf commands
# Uses jq for JSON parsing (needed for nested fields like tool_input.command)

input=$(cat)
command=$(echo "$input" | jq -r '.tool_input.command // ""')

# Block rm -rf commands
if [[ "$command" =~ "rm -rf" ]]; then
    echo '{"decision": "deny", "reason": "rm -rf commands are blocked for safety"}'
    exit 2  # Exit code 2 = block the operation
fi

exit 0  # Exit code 0 = allow the operation

log_tools.sh - PostToolUse hook

#!/bin/bash
# PostToolUse hook: Log all tool usage
# Uses OPENHANDS_TOOL_NAME env var (no jq/python needed!)

# LOG_FILE should be set by the calling script
LOG_FILE="${LOG_FILE:-/tmp/tool_usage.log}"

echo "[$(date)] Tool used: $OPENHANDS_TOOL_NAME" >> "$LOG_FILE"
exit 0

inject_git_context.sh - UserPromptSubmit hook

#!/bin/bash
# UserPromptSubmit hook: Inject git status when user asks about code changes

input=$(cat)

# Check if user is asking about changes, diff, or git
if echo "$input" | grep -qiE "(changes|diff|git|commit|modified)"; then
    # Get git status if in a git repo
    if git rev-parse --git-dir > /dev/null 2>&1; then
        status=$(git status --short 2>/dev/null | head -10)
        if [ -n "$status" ]; then
            # Escape for JSON
            escaped=$(echo "$status" | sed 's/"/\\"/g' | tr '\n' ' ')
            echo "{\"additionalContext\": \"Current git status: $escaped\"}"
        fi
    fi
fi
exit 0

require_summary.sh - Stop hook

#!/bin/bash
# Stop hook: Require a summary.txt file before allowing agent to finish
# SUMMARY_FILE should be set by the calling script

SUMMARY_FILE="${SUMMARY_FILE:-./summary.txt}"

if [ ! -f "$SUMMARY_FILE" ]; then
    echo '{"decision": "deny", "additionalContext": "Create summary.txt first."}'
    exit 2
fi
exit 0

Next Steps

• See also: Metrics and Observability
• Architecture: Events