Online Tool Store
· 6 min read
3 Random File Generator Tools, Compared Honestly
Manesh Jayawardhana
CIO & Co-founder
You need a dummy file of a specific size — to test an upload limit, check storage quota behavior, or verify compression handling — without hunting down a real file that happens to be the right size.
Every generator here produces a file at your chosen size; the differences are in the maximum size supported, what fill-byte pattern is used (which affects compressibility for testing purposes), and how many file formats and extensions are available.
How to judge a random file generator tool
Offers the fill-byte option that matches your test. Random bytes are incompressible (honest for throughput testing), zero bytes compress extremely well (useful for testing gzip/CDN compression specifically), and text or pattern fills suit other scenarios like log parser testing — the wrong fill type can give misleading test results.
Supports the size range you need. A tool capped at a few hundred MB won’t help for testing large-file upload limits or storage quotas in the multi-GB range.
Generates the actual file format when that matters. A file with correct magic bytes and valid structure (a real PDF, a real ZIP) behaves differently in MIME validation than a renamed binary blob — check whether the tool produces spec-compliant files if your test depends on that.
Processes entirely client-side. Generating a large file shouldn’t require uploading anything or waiting on a server round trip — local generation with direct download is the expected behavior.
The comparison
| Tool | Best for | Free tier | Watch out |
|---|---|---|---|
| dummyfiles.dev | Simple size range (1KB-5GB) with random or zero fill for compression testing | Free, no signup | Fewer format options (6) than SarvKit’s broader range |
| SarvKit | Widest format range (25 formats) with spec-compliant magic bytes for real MIME validation | Free, no signup, client-side | Structured formats round up to a minimum size below which exact sizing isn’t possible |
| Tembrica | Largest size range (up to 10GB on Chromium) with 4 distinct fill-byte patterns | Free, optional account for bookmarking | Safari/Firefox have lower size limits than Chromium due to browser API differences |
| Random File Generator | Text, binary, CSV, or JSON dummy files at a chosen size | Free, no signup | Fewer format options and fill-byte patterns than the alternatives |
Facts checked August 2026; tools change their plans.
dummyfiles.dev
dummyfiles.dev generates test files from 1 KB to 5 GB in ZIP, BIN, JPG, PNG, WebP, or PDF format, with two fill modes — random bytes (hardly compressible, for honest throughput testing) or zero bytes (compresses very effectively, useful for ZIP/compression testing specifically) — free with no signup, designed for developers and QA teams validating upload limits and compression behavior.
It isn’t for someone who needs a wide format selection — its 6 formats are fewer than SarvKit’s 25-format range.
SarvKit
SarvKit generates byte-exact dummy files across 25 formats — PDF, PPTX, ZIP, DOCX, XLSX, PNG, JPG, MP4, WAV, JSON, CSV, BIN, and more — entirely client-side using the Web Crypto API, with real, spec-compliant magic bytes so generated files pass actual MIME validation, streaming to disk for files up to 5GB on Chromium, batch generation of up to 20 files at once, and popular presets for common testing scenarios.
It isn’t for someone needing an exact tiny size on a structured format — requests smaller than a format’s minimum overhead (like a very small PDF or ZIP) get rounded up with a warning rather than producing a truly undersized structured file.
Tembrica
Tembrica generates dummy files from 1 KB up to 10 GB (using the File System Access API on Chromium; 1 GB cap on other browsers), with four fill-byte options — zeros (highly compressible, good for gzip/CDN testing), random (cryptographically random, incompressible for honest throughput tests), ASCII text (repeating Lorem ipsum, useful for testing log parsers and text indexers), and pattern (a cyclic byte ramp visually identifiable in a hex editor) — plus six custom extensions (.bin, .dat, .iso, .txt, .zip, .raw), entirely client-side.
It isn’t for someone on Safari or Firefox needing very large files — those browsers assemble files in memory with notably lower size limits than Chromium’s streaming approach.
Random File Generator
Our tool generates a dummy file of a chosen size and type — text, binary, CSV, or JSON — filled with placeholder content, ready to download for testing uploads or storage limits, entirely in your browser.
A real limitation: it offers fewer format options and fill-byte pattern choices than the alternatives — for spec-compliant structured formats (real PDFs, ZIPs) or specific compression-testing fill patterns, SarvKit or Tembrica cover that additional need.
Which one to pick
If you want a quick text, binary, CSV, or JSON file at a chosen size, use our Random File Generator.
If you need a real, spec-compliant file format (PDF, DOCX, ZIP) that passes MIME validation, use SarvKit.
If you’re testing compression behavior specifically and need zero-byte fill, use dummyfiles.dev or Tembrica.
If you need the largest possible file size (up to 10GB) or specific fill patterns like a hex-visible byte ramp, use Tembrica.
How to do it with Random File Generator
- Open the Random File Generator.
- Choose your file type — text, binary, CSV, or JSON — and target size.
- Download the generated dummy file for testing uploads or storage limits.
Browse the full tools directory for more free, browser-based generators.
Frequently asked questions
Is there a free random file generator that doesn’t need an account?
Yes. Our Random File Generator and all three alternatives here work without requiring signup.
Why does the fill-byte pattern matter for testing, not just the file size?
The actual size of a file often matters less than how compressible its content is — a file filled with zero bytes compresses down to nearly nothing, which is misleading if you’re trying to test real upload bandwidth or storage usage, while random bytes are essentially incompressible and give an honest picture of throughput. Choosing zero-fill when you actually need random-fill (or vice versa) can produce test results that don’t reflect real-world behavior.
When would I need an exact, spec-compliant file format instead of a generic binary blob?
If your test involves an upload endpoint that validates MIME type or file structure (checking that a “PDF” upload is actually a valid PDF, not just a file renamed with a .pdf extension), a generic binary blob will get rejected by that validation even though its size is correct — for that scenario, a generator that produces real, spec-compliant magic bytes and file structure (like SarvKit’s approach) is necessary rather than a size-only dummy file.
Final thought
Match the fill-byte pattern to what you’re actually testing — zero-byte files are great for a quick size check but will give a wildly misleading result if you’re specifically testing upload throughput or storage compression behavior, where random-byte incompressible content is the honest choice.