It can be difficult to know what your seed is especially if you're using a dedicated server. If you tried to type in your seed but got a completely different world your seed might not be what you thought. For example, make sure you're using the world seed and not the world name.
Instead, by uploading or dropping your .fwl file to this page your seed will be automatically determined and is guaranteed to be correct.
If even after using this tool your seed is still wrong check out the About page in the links above.
Extracting your seed
To get started just click "Choose File" and select your .fwl or .fwl.old file OR just drop the file directly onto this page. If you're using a dedicated server you'll have to download this file using the steps from your host.
For windows users click "Choose File" and then paste this into the file name "%appdata%\..\locallow\IronGate\Valheim\worlds" (NO Quotes!) Then just select the .fwl with your world's name.
Linux users may be able to find their seed under the path: "~/.config/unity3d/IronGate/Valheim/worlds/" Select the .fwl, not the .db files.