Audit and apply the Player Settings, compression, stripping, and server setup that make a Unity Web build smaller and faster.

Important

Use the unity cli (unity command --format json) and the unity-cli skill for each step. Use unity-pipeline too when it is available.
Before making changes, establish a baseline of the current behavior so you can tell whether a later result is actually caused by your change.
Create a restore point you can roll back to if your changes fail.
Do only what's asked. Don't change unrelated assets or files.
If the changes affect runtime behavior, add Debug.Log lines that will prove the actual scene behaviour (not just your changes) is now working - you'll read these when you enter Play mode to validate later. For example, log a GameObject's Transform scale if your fix is meant to make sure it changes size.
Avoid long explanations.

Performance Notes

Before you go forward with a workflow or diagnosis: