How to inspect a file's gzip compressibility

1. Upload any file

   Drop the file you want to analyse into the File field. accept is */* — text, binaries, archives, images, anything. Size is capped at the configured maximum (decoded base64 length is enforced).

2. What the tool checks

   It detects whether the file starts with gzip magic (0x1f 0x8b), tries to gunzip it, and (whether or not the upload was already gzip) re-gzips the underlying payload at a fixed zlib level for reference.

3. Press Run

   Output returns originalBytes, isGzipCompressed, optional gzipHeaderExtraFlags / gzipHeaderXflByte (if the file IS gzip), uncompressedBytes, referenceZlibLevel, gzipBytes, ratio, and savingsPercent.

4. Read the note

   Zlib levels 1–9 are NOT stored inside .gz files — the gzip header XFL byte only records the compressor's MODE (fastest / normal / maximum). "Reference re-gzip size" is what zlib at this tool's fixed level would have produced; it's a sanity baseline, not a guarantee of best-possible compression.