Business card file preflight
Drag in the PDF or image you have and read it locally: is there 3mm bleed, what's the trim size, are fonts embedded, is the bitmap 300dpi, and are vector colours already separated to CMYK. No file is uploaded; parsing happens entirely in your browser.
What it can't check
Proofing colour, spot inks (DeviceCMYK only says four inks are used, not that separation followed an ICC intent), and whether text hugs the edge when there's no ArtBox — only a physical proof settles those. Files from this site write TrimBox / BleedBox / ArtBox explicitly and, with CMYK on, keep total ink under 250%, so preflighting our own files is the most accurate.