quality

quality/<1 to 100>

Sets the compression quality. It applies to JPEG and WebP, and does nothing for a lossless format.

quality/70

The value only ever lowers. A request for a higher quality than the source already has is ignored, because raising it adds bytes without adding detail.

A value outside 1 to 100 is refused with 400, and so is one that is not a number. A leading zero is decimal, so quality/070 means 70.