Generate Dummy Files of Any Size for Testing

A free tool for generating dummy files of arbitrary size — useful for testing upload limits, network throughput, disk benchmarks, S3 multipart uploads, and antivirus behaviour against opaque binary blobs. Pick a size, choose a byte-fill mode (zeros, cryptographic random, ASCII text, or repeating 0–255 pattern), and the file streams to disk via the File System Access API when available.

How to Use

Enter the target size and pick the unit (KB / MB / GB).

Choose how the bytes should be filled — zeros for compressible, random for honest network tests, text or pattern for log-parser fixtures.

Customise the filename and extension if the default does not match your scenario.

Click Generate — your browser will prompt you to choose a save location (if File System Access is supported) or download a Blob.

Use the file to test upload limits, disk write speed, S3 multipart, or any other size-bound flow.

Create test files from 1 KB to 10 GB directly in your browser

File size 1 KB – 10 GB

= 104 857 600 B

Byte content

Zeros All 0x00 — highly compressible, good for testing gzip / CDN compression. Random Cryptographically random — incompressible, honest throughput tests. ASCII text Repeating Lorem ipsum — fixture for log parsers and text indexers. 0–255 pattern Cyclic byte ramp — visually identifiable in a hex editor.

Filename

Detecting browser capabilities…

Writing bytes… 0%

0 / 0

Features

Any size from 1 KB up to 10 GB (with File System Access API) or 1 GB on other browsers Four fill modes: zero, cryptographic random, ASCII text (Lorem), repeating byte pattern Six extensions to match your test scenario: .bin, .dat, .iso, .txt, .zip, .raw Streams chunk-by-chunk so a 5 GB output never holds the full file in RAM Cancel anytime — partial output is discarded, no half-written files

Frequently Asked Questions

What is a dummy file used for?

Dummy files have a known size and known byte content, so they let you isolate the variable you actually care about — network bandwidth, disk write speed, server-side upload limit, compression ratio, S3 multipart chunking. Without dummies, every test is contaminated by the unpredictability of real files.

What is the difference between zero, random, text and pattern fill?

Zero-filled (0x00) bytes compress to almost nothing — ideal when you want to verify that gzip or a CDN is actually deflating responses. Random bytes are incompressible and reflect real-world throughput (compressing proxies cannot cheat). ASCII text is suitable for log-parser and text-indexer fixtures. The 0–255 byte pattern is visually identifiable in a hex editor, which is handy when diagnosing whether an upload arrived truncated.

How does a 10 GB browser download even work?

On Chromium-based browsers we use the File System Access API: showSaveFilePicker hands us a writable stream, and we write 4 MiB chunks straight to your chosen file on disk, never holding the whole file in memory. On Safari and Firefox the file is assembled as a Blob in memory and the cap is around 1 GB to avoid tab crashes.

How is the file produced?

Bytes are generated by JavaScript and streamed to your local disk via the File System Access API (Chromium) or held in a Blob (Safari, Firefox). The whole pipeline is client-side — that is how the tool can produce a 10 GB file fast without round-tripping it. Aggregate usage telemetry (which size buckets people pick, which fill modes) is sent so we know which presets to add next.

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Published 21 May 2026