1. How the formats differ
GIF uses a palette with up to 256 colors per frame. WebP supports lossy and lossless compression and animation. Which output is smaller depends on the content and encoding settings; compare actual files rather than assuming a fixed saving.
2. Browser display and upload acceptance differ
A browser may display a format that a board or editor does not accept. Test the real destination and check that the uploaded result still moves and shows its background as intended.
3. Choose for the destination
Use GIF where the upload location requires GIF. On a web page that accepts other formats, compare WebP or video at the same displayed size and similar visual quality. Consider animation, transparency and available editing workflows together.
4. What this tool supports
The current tool reads GIFs and saves GIFs; it does not offer WebP conversion. If the result must remain a GIF, adjust dimensions, colors, frames and the timeline. Use a separate converter for other formats and verify its output.