SVG is the most common file customers send for laser engraving and cutting, and also one of the easiest to get subtly wrong. These are the requirements that matter most, with how to fix each one in Inkscape or Illustrator.
A laser follows vector paths for cutting and scoring. Shapes such as rectangles and circles are usually fine, but the safest file has everything converted to paths. In Inkscape use Path > Object to Path; in Illustrator, Object > Expand.
An SVG can keep text as a <text> element that depends on a font. If the machine computer does not have that font, the text is replaced by another font or disappears. Before sending, select the text and convert it: Inkscape Path > Object to Path, Illustrator Type > Create Outlines. You can verify by opening the SVG in a text editor and searching for <text: there should be none.
A photo or PNG pasted into an SVG is still a bitmap. It can be engraved as an image, but it cannot be cut. If you need a cut outline, trace it to vectors (Inkscape Path > Trace Bitmap) and check the result.
SVG sizes depend on the width, height and viewBox attributes. Set the document in millimetres or inches with the real final size, so the design imports at 1:1. A mismatch between programs that assume 72 or 96 DPI is a classic cause of designs arriving 25% too small or too large.
Many shops use thin strokes (for example 0.01 mm or hairline) in a specific colour for cuts, and filled areas for engraving. Follow the colour code your shop publishes, and remove unused colours.
Cut outlines should be closed paths, and stacked duplicate paths should be removed so the laser does not burn the same edge twice.
Ungroup and clean up hidden layers, unused definitions and metadata (Inkscape File > Clean Up Document, then save as Plain SVG or Optimized SVG). Simplify traced paths that have thousands of nodes.
If you run a Shopify store where customers upload files, CutReady checks supported SVG (up to 256 KB), ASCII DXF (up to 512 KB) and PDF (up to 2 MiB) files on the product page before add-to-cart, and blocks files that fail with a clear message. 14-day free trial, then 39 USD every 30 days.