The problem with manual stop-loss monitoring: you check your phone, the market moves while you're not watching, and you exit a position three points below where you meant to.

Here's how I built an automated stop-loss monitor that sends a Telegram alert within 2 seconds of a threshold breach — using Claude Code, Yahoo Finance's free API, and a SKILL.md file.

No broker API. No paid data service. No authentication flow.

How it works

The skill polls Yahoo Finance's undocumented quote endpoint every 5 minutes during market hours:

https://query1.finance.yahoo.com/v8/finance/chart/{ticker}?range=1d&interval=1m

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When the current price crosses a configured threshold, it fires a Telegram alert and logs to a 30-minute deduplication cache (so you don't get spammed if a stock bounces around a level).

Market hours detection

No point running the monitor at 3am or on weekends.…