ChangeDetection.io — MCP Server & Hermes Skill

Overview

ChangeDetection.io is a self-hosted or SaaS tool for monitoring web pages for changes — price drops, restock alerts, content updates, defacement monitoring. It's one of the most popular self-hosted tools (31k+ GitHub stars).

This skill pairs the changedetection-mcp MCP server with Hermes-native features (cron scheduling, multi-platform delivery) to create a powerful watch-and-notify loop.

When to Use

• User asks to "watch this page" or "monitor this URL for changes"
• User needs to be notified about price drops, restocks, or content updates
• User wants to check what changed on a page overnight
• User wants to set up recurring checks with delivery to Telegram/Discord/email

Don't use for: One-off checks (use web_extract or browser_navigate instead). This is for ongoing monitoring.

Prerequisites

1. ChangeDetection.io instance — self-hosted at http://localhost:5000 (or any URL) or use the SaaS plan at https://changedetection.io
2. API key — found in Settings → API tab in the ChangeDetection.io dashboard
3. changedetection-mcp installed — pip install changedetection-mcp (or run from source)

Setup

Option A: MCP Server (any MCP client)

Add to your MCP configuration:

{
  "mcpServers": {
    "changedetection": {
      "command": "changedetection-mcp",
      "env": {
        "CHANGEDETECTION_BASE_URL": "http://localhost:5000",
        "CHANGEDETECTION_API_KEY": "your-api-key"
      }
    }
  }
}

Option B: Hermes Config (recommended for Hermes users)

# Install the MCP server
pip install changedetection-mcp

# Add as an MCP server to Hermes
hermes mcp add changedetection --command "changedetection-mcp"

Then set env vars in ~/.hermes/.env:

CHANGEDETECTION_BASE_URL=http://localhost:5000
CHANGEDETECTION_API_KEY=your-api-key

Usage Examples

Create a watch

Can you watch https://example.com/product-page for price changes? Check hourly.

The agent will call create_watch with the URL and check interval.

List my watches

Show me all my active watches.

→ Calls list_watches()

Check for changes

What changed on my watched page in the last 24 hours?

→ Calls get_watch_history() then get_snapshot_diff(). The diff call arms the per-watch action fuse, limiting follow-up mutating actions for that watch.

Control follow-up action limits

Show me what changed on this noisy watch, but allow at most one follow-up action.

→ Calls get_snapshot_diff(..., action_limit=1). Use action_limit=0 only when the user explicitly wants the fuse disabled for that watch.

Set up persistent monitoring with cron

Every morning at 9am, check all my watches and send me a summary of what changed.

→ The agent can set up a Hermes cronjob that queries changedetection and delivers to your home channel.

Pause/resume

Pause the watch on example.com till next week.

→ Calls update_watch(paused=True)

Common Pitfalls

1. API key not set — The MCP server will exit with an error if CHANGEDETECTION_API_KEY is missing. Always set it in .env or the MCP client config.
2. Self-hosted URL wrong — Default is http://localhost:5000. If using Docker with a different port or host, set CHANGEDETECTION_BASE_URL explicitly.
3. `latest`/`previous` in diff — These are convenience aliases for the most recent snapshots. If no changes occurred, the diff will be empty.
4. Watches created paused — New watches start active by default. Pass paused=True to create_watch if you want to set up but not start monitoring yet.
5. Rate limiting — Setting minutes_between_checks too low (under 5 minutes) may get you rate-limited, especially on the SaaS plan. 1 hour is a safe default.
6. Noisy diff cascades — get_snapshot_diff arms a per-watch action fuse (default 3) so one noisy page cannot trigger unlimited recheck_watch, update_watch, or delete_watch calls. Raise action_limit only when needed; set CHANGEDETECTION_MCP_ACTION_LIMIT_PER_WATCH=0 or call with action_limit=0 to disable.

Verification Checklist

• [ ] changedetection-mcp runs without errors: CHANGEDETECTION_BASE_URL=... CHANGEDETECTION_API_KEY=... changedetection-mcp
• [ ] list_watches returns your existing watches
• [ ] create_watch can add a new URL
• [ ] get_snapshot_diff returns meaningful diffs (test with a URL you know changes)
• [ ] Hermes cron delivery works end-to-end if using scheduled checks

Config Reference

MCP Tool Reference