What job block makes a villager into a Farmer?

The job block that makes a villager into a Farmer is a Composter. Place it near an unemployed villager, and they can claim it as their job site block and become a Farmer.

How it works

• The villager must be unemployed.
• The composter must be reachable.
• Once claimed, the villager changes profession to Farmer.

Quick note

If the villager already has a job, you usually need to break their current job block first so they can take the composter.

Tiny example

Put a composter next to an unemployed villager in a village, wait a moment, and they should switch to a Farmer, often with green particles showing the job change.

TL;DR: Composter.