Where can developer commands be used?

Toggle them by entering "devcommands" in the console. They are available in single-player and manually hosted games, but they do not work on dedicated servers.

Which commands change achievement eligibility?

Most commands, such as "spawn", permanently flag the current character and world against achievements. Some commands, including "freefly", are exceptions.

What happens when a spawned item is picked up?

Spawned items carry a cheat mark. Picking one up places an eligible character into a temporary cheat state, which locks achievement unlocking. Throwing all cheated items out of the inventory makes the character eligible for achievements again.

Valheim Console Commands

Enable the console, distinguish ordinary access from developer-command mode, and protect achievement eligibility from accidental cheat-state changes.

Open the console safely

Add "-console" to the launch options, then press F5 in the game to open the console. Enter "devcommands" to enable cheat commands and enter it again to disable them. Cheat commands work in single-player or manually hosted mode, not on a dedicated server.

Treat developer commands as a permanent-save decision: most commands, including "spawn", flag the current character and world so they are permanently locked out of achievements. "freefly" is one documented exception.

Cheat-state consequences and recovery

Where can developer commands be used?: Toggle them by entering "devcommands" in the console. They are available in single-player and manually hosted games, but they do not work on dedicated servers.
Which commands change achievement eligibility?: Most commands, such as "spawn", permanently flag the current character and world against achievements. Some commands, including "freefly", are exceptions.
What happens when a spawned item is picked up?: Spawned items carry a cheat mark. Picking one up places an eligible character into a temporary cheat state, which locks achievement unlocking. Throwing all cheated items out of the inventory makes the character eligible for achievements again.