Start with two questions

Which formats does the destination accept? Does the image need transparency? Those two questions matter more than chasing the smallest file at any cost.

FormatHow to use it in Toolhe
JPGUse when JPG is required and transparency is unnecessary. This tool fills transparent areas with white.
PNGAn option for preserving transparency. The Canvas PNG encoder does not use the quality slider; output may be larger.
WebPTry it when the destination supports WebP. Adjust quality and compare the actual size and visual result.

Keep the original, then convert

Toolhe creates a new file without overwriting the original. Re-encoding may remove metadata. Inspect text edges, fine lines and gradients, and remember that converting an optimized file does not necessarily make it smaller.

The current web tools process static JPG, PNG and WebP, one file at a time. They do not decode HEIC or preserve animation.
Open the image converter

Technical reference: MDN · HTMLCanvasElement.toBlob()