Flags Reference

All flags are optional. Shrinkr has sensible defaults for every setting.

Full Table

Flag	Short	Type	Default	Description
`--format`	`-f`	string	`webp`	Output format: `webp`, `avif`, `jpeg`, `png`
`--size`	`-s`	int	`500`	Target file size in KB
`--output`	`-o`	string	`compressed`	Output folder path
`--quality`	`-q`	int	`85`	Initial quality (1–100) for first compression attempt
`--workers`	`-w`	int	CPU count	Number of concurrent workers (auto-detected)
`--recursive`	`-r`	bool	`false`	Also scan subdirectories
`--min-quality`	—	int	`60`	Quality floor — compression won't go below this
`--max-quality`	—	int	`90`	Quality ceiling — compression won't exceed this

--workers defaults to runtime.NumCPU() — the number of logical CPU cores on your machine. On Apple Silicon M-series chips this is typically 8–12. You rarely need to change this.
--min-quality and --max-quality define the search range for the binary search algorithm. A narrower range means fewer iterations but may not hit the target size.
--quality is the starting point. If the image is already under the target size at this quality, Shrinkr stops immediately (no binary search needed).
--recursive (-r) scans all subdirectories. The output folder mirrors the input directory structure.
--min-quality must be less than or equal to --max-quality, or Shrinkr will exit with an error.

Format	Characteristics
`webp`	Best default. Excellent quality-to-size ratio. Supported by all modern browsers.
`avif`	Smaller files than WebP but slower to encode. Good for batch jobs where speed isn't critical.
`jpeg`	Maximum compatibility. Use for clients or platforms that don't support WebP.
`png`	Lossless. File size depends entirely on image complexity — target size may not be reachable for complex images.