The OG ToggleSneak back in 1.7.10. Supports toggling sneaking, sprinting, and fly boosting.
Note: Fly boosting only works on creative mode and it may not be allowed by some servers.
Note: Sneak toggling may be considered bannable on some servers. Please refer to their server rules. You can disable this feature via options.
Originally coded by u/ScrobDobbins. Updated by Ringosham for newer Minecraft versions.
Requires PlayerAPI. Obtainable in this GitHub repository
Screenshot: (You can see this is Minecraft 1.12 because of terracotta blocks)
Please report any bugs in the issues page
If somebody can contribute a better icon that would be nice...
Also if there's enough demand I might update this for newer versions of Minecraft