Platform
Message Content Intent
The privileged intent required to read what a message actually says. Without it a bot receives the message event but an empty content field, except in DMs and for its own mentions.
This is why most third-party analytics tools count events rather than read text: counting needs no privileged intent, and requesting one that is not needed makes approval harder.
Any bot offering keyword filtering on message text needs this intent, which is worth knowing when judging whether a small self-hosted filter will keep working as it grows.