Exact-size Test File Generator

How to use Exact-size Test File Generator

Generate a real local binary test file with an exact byte count, explicit contents and a SHA-256 checksum. Choose zero bytes, a short repeated hex cycle or Web Crypto random bytes. Test controlled upload limits and storage behavior without pretending the file is a valid image or document.

1. Provide exact output bytes, hex cycle for cyclic mode only.
2. Choose the supported mode and run the tool. Review its assumptions and any reported errors.
3. Copy the result or download a separate output; reset to clear the current form.

Good to know

• Generate exactly 0–8,388,608 bytes in one .bin file. The size control uses bytes, not decimal MB or binary MiB conversion. A zero-byte output is valid and remains explicitly empty.
• Cyclic mode accepts 1–128 complete unseparated hex bytes, at most 256 hex characters; the final repetition may be truncated to meet the exact requested size. Zero/random modes do not use the cycle text.
• Random mode uses native Web Crypto getRandomValues in chunks of at most 65,536 bytes. There is no reproducible seed or claim that generated random contents will be unique. Deterministic patterns are intentionally unsuitable as random secrets.
• SHA-256 is calculated over the actual output bytes. An 8 MiB output plus retained byte/digest/Blob copies has a bounded input-independent size, but browser memory use varies. No file is automatically uploaded or written to an external application.
• The .bin is arbitrary data. A chosen byte size or checksum does not make a valid PDF, ZIP, video or image, bypass a service restriction or prove upload acceptance. Compression ratio and server-side treatment depend on the selected pattern and target system.
• Structured text output is limited to 500,000 characters. Reduce the supplied source when that separate output budget is exceeded.
• Inputs are processed on this device and are not automatically saved or uploaded.