While watching the URL, when it detects any changes it will send diffs of web pages as they change.

Here are some key features of "urlwatch":

· Can run as a cronjob and mail changes
· Easily customizable
· Always outputs only plaintext, no HTML emails
· Supports removing noise (always-changing website parts)
· Example hooks to filter content in Python
· Uses If-Modified-Since header to save bandwidth
· Convert non-UTF8 web pages to UTF-8 for mail
· Handle non-zero shell exit codes as error