Is this really a XLSX?
Drop a file with a .xlsx extension and we will compare its magic bytes to the XLSX (Microsoft Excel spreadsheet) signature. Bytes never leave your browser.
Check a file
Drop a XLSX file (.xlsx) to verify it really is what its extension claims.
Drop your image here or click to upload
Drop any file (max 50 MB) to see whether the contents match the extension.
Processed 100% in your browser
We read the first few bytes of your file locally. Nothing is uploaded, nothing is saved.
How we check
Every XLSX file starts with a fixed sequence of bytes called a magic-byte signature. We read the first few bytes of the file you drop, compare them against the signature for Microsoft Excel spreadsheet, and report MATCH, MISMATCH, AMBIGUOUS, or UNKNOWN. On desktop we also run an AI content classifier on ambiguous content, locally in your browser.
Nothing is uploaded. The bytes never leave your device. Read the full data flow on the Magic numbers explainer.