api-monitoring-bots

API Monitoring Bots

Build lightweight monitoring bots that poll REST APIs and send notifications when state changes (new items, price alerts, status updates).

When to Use

• User wants notifications for new listings/posts/items
• Need to track price changes or threshold alerts
• Monitor API for specific conditions
• Watchdog for service status changes

Architecture Pattern

Stateful polling bot:

1. Fetch current state from API
2. Compare with last known state (stored in file)
3. Detect changes (new IDs, price deltas, status transitions)
4. Format and send notifications
5. Update state file

Key principle: Silent when no changes (watchdog pattern, no spam).

Implementation

1. Core Script Structure

#!/usr/bin/env python3
import requests
import json
from pathlib import Path
from datetime import datetime

API_URL = "https://api.example.com/items"
STATE_FILE = Path.home() / ".hermes" / "monitor_state.json"

def load_state():
    """Load last seen state"""
    if STATE_FILE.exists():
        with open(STATE_FILE) as f:
            return json.load(f)
    return {"seen_ids": [], "last_check": None}

def save_state(state):
    """Save current state"""
    STATE_FILE.parent.mkdir(parents=True, exist_ok=True)
    with open(STATE_FILE, "w") as f:
        json.dump(state, f, indent=2)

def fetch_items():
    """Fetch current items from API"""
    try:
        r = requests.get(API_URL, timeout=10)
        r.raise_for_status()
        return r.json()
    except Exception as e:
        return None

def check_new_items():
    """Check for new items and return notifications"""
    state = load_state()
    items = fetch_items()
    
    if not items:
        return []
    
    seen_ids = set(state["seen_ids"])
    new_items = []
    
    for item in items:
        if item["id"] not in seen_ids:
            new_items.append(item)
            seen_ids.add(item["id"])
    
    # Update state (keep last 1000 IDs to prevent bloat)
    state["seen_ids"] = list(seen_ids)[-1000:]
    state["last_check"] = datetime.now().isoformat()
    save_state(state)
    
    return new_items

# Initialize state on first run (don't notify)
state = load_state()
if not state["seen_ids"]:
    items = fetch_items()
    if items:
        state["seen_ids"] = [item["id"] for item in items]
        state["last_check"] = datetime.now().isoformat()
        save_state(state)
        print(f"Initialized with {len(state['seen_ids'])} existing items")

# Check for new items
new_items = check_new_items()

if new_items:
    for item in new_items:
        print(format_notification(item))
# Silent when no new items (watchdog pattern)