Try the Commands Troubleshooting and Help page if you get stuff with server errors.
Minecraft summon mule command
Using the summon command to spawn in a minecraft mule is simple, take the command and enter into chat and presto you have a mule. Mules share many of the same tags for horses. Mules also have the ability to have chests.
How to summon a mule with chest contents
You can set the chest items by using the items tag, this only works if the ChestedHorse is set to true. The Tame tag will also help with chest access.
/summon minecraft:mule ~ ~ ~ {ChestedHorse:1,Items:[{id:red_carpet,Count:1,Slot:2},{id:green_carpet,Count:1,Slot:4},{id:blue_carpet,Count:1,Slot:7}],Tame:1}How to summon a baby mule (foal)
Like most passive mobs in Minecraft, you can summon a foal by setting the Age tag to a negative number (under the "Additional" tab).
/summon minecraft:mule ~ ~ ~ {Age:-1200} (Grows up in 60 seconds)/summon minecraft:mule ~ ~ ~ {Age:-6000} (Grows up in 5 minutes)
Summon mule owned by player, Owner NBT Data Tag (1.16+)
You can set which player owns the mule by setting the UUID, which is now a int-array.
/summon minecraft:mule ~ ~ ~ [I;-132296786,2112623056,-1486552928,-920753162]Summon mule owned by player, OwnerUUID NBT Data Tag (before 1.16)
You can set which player owns the mule by setting the UUID.
/summon minecraft:mule ~ ~ ~ {OwnerUUID:00000000-0000-0000-0000-000000000000}Suggestions or found a bug
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If you're looking for a particular summon mob generator you can link to these specific versions of the command generator.