Yes by default. The five lossless passes — strip comments, strip metadata, strip editor data, remove unused defs, minify whitespace — operate purely on markup the renderer never reads. The sixth pass, decimal precision rounding, is mathematically lossless at sub-pixel detail (3 decimals = 1/1000th of a viewport unit) but is opt-out if you need exact precision for plotting or CAD-style work.

Vector editors embed their own state in your SVG so they can re-open it as if it were a project file. Inkscape adds `<sodipodi:namedview>` blocks describing the canvas, layer order, and document grid; Illustrator adds `<!-- Generator: Adobe Illustrator -->` comments and `<i:` namespaced attributes; Sketch and Figma add their own equivalents. None of it renders — but it can balloon a 5 KB icon to 25 KB.

Default 3 decimals is the sweet spot — sub-pixel at any normal viewport zoom. Drop to 2 for icons displayed under 64×64 (no visible difference). Stay at 4–6 for SVGs that get plotted, embroidered, or used as CAD blueprints. The default 3 reliably saves 20–30% of the path-data bytes with zero visible compromise.

No. The optimizer preserves SMIL animation elements, CSS classes, IDs referenced by `<use>` and `xlink:href`, JavaScript event handlers, and aria attributes. The unused-defs pass walks the document graph before removing — so any def that's referenced anywhere stays. If you've got animated SVG, run the optimizer; the animations keep working.

Yes. Drop a folder, set the six-pass profile once, and the runner applies it across every SVG in the queue. Pair with the Convert track in a recipe if you also need raster fallbacks for older browsers — the chain ships SVG + WebP fallback in a single zip.

No. The XML parser, the optimization passes, and the markup writer all run in your browser tab. SVG is text — even less of an excuse to ship it to a server than raster images. Source bytes stay on-device; only the optimized output you save touches your disk.