Know the checks before trusting a result.
FileDoctor uses browser-local JavaScript to recognize selected formats and check limited structural facts. Individual tools explain their own scope.
Archives and compressed data
ZIP: Inspect directory and entry records and verify CRC32 when the compression method is supported. Encrypted or unsupported methods cannot be silently treated as verified. GZIP: Inspect the header and, when the browser can decompress the stream, check decoded length and CRC32. TAR: Inspect record alignment and header checksums, not every contained file. RAR and 7z are signature-detected only; no general repair or extraction is promised.
Pictures and media
PNG: Verify chunk structure and CRC32, not complete visual decoding. JPEG, GIF, WebP, BMP and ICO: Inspect selected signatures, markers or boundaries. JPEG EXIF removal targets recognized APP1 EXIF data, but other metadata may remain. MP4-family: Inspect basic atom/box structure rather than decoding video. WAV: Check RIFF chunks and optionally correct the container-length field on a downloaded copy. MP3 and FLAC checks focus on selected headers, not complete audio decoding.
Documents, data and databases
PDF: Check key header/trailer markers, not complete page rendering. JSON/JSONL and CSV: Validate or conservatively normalize supported text formats. JSONL salvage may omit malformed records and should be reviewed before importing. SQLite: Read the file header and selected size/page settings, not full database integrity. Text/Base64: Analyze or decode within the browser when valid.
Size and browser requirements
Files are limited to 64 MB each, with additional decompressed-output limits. Some compression features depend on DecompressionStream. Cryptographic hashing depends on a secure HTTPS context. Safari, Firefox, Chrome and mobile browsers may differ. Unsupported features must be reported as unsupported, not as a passed diagnostic.
For full explanations read the testing methodology and troubleshooting help. To see every available test, browse the 34 diagnostic tools.