Question 1

What is the difference between MB and MiB when generating a file?

Accepted Answer

1 MB is 1,000,000 bytes and 1 MiB is 1,048,576 bytes, a 4.86% difference. The same goes for KB (1,000) and KiB (1,024), GB (1,000,000,000) and GiB (1,073,741,824). NIST notes that memory makers often use megabyte for 1,048,576 bytes and storage makers for 1,000,000, so the tool shows the size in both systems and lets you pick the unit.

Question 2

Are the files valid or do they just have the right extension?

Accepted Answer

They are valid. The PDF opens in common readers, the PNG and JPG decode, the ZIP passes the integrity test and the WAV plays. What they lack is useful content: the PNG is a gradient or a solid color, the JPG is a mosaic of 8x8 blocks, the PDF holds the text Dummy test file. They are made to pass type and size validation, not to test rendering.

Question 3

Why do some sizes return a minimum size error?

Accepted Answer

Each format has a floor. With default options a one-page PDF needs about 900 bytes, a PNG 69 bytes (1x1 pixel), a JPG about 350, a WAV 44 and a ZIP 122 with one empty file. The PNG also accepts only the natural size of the image or that size plus 12 bytes or more, because the smallest padding chunk is 12 bytes. The tool reports the minimum and offers a button to use it.

Question 4

What is the largest size I can generate?

Accepted Answer

1 GiB (1,073,741,824 bytes) on computers, 256 MiB on touch screens, and 256 MiB for CSV and JSON, which are generated row by row. These are conservative caps chosen to avoid exhausting browser memory, and they were not measured in every browser. Repetitive files (zeros, text) are added by reference and barely use memory; random ones take their full size.

Question 5

How do I test the upload limit of a server or form?

Accepted Answer

Use Upload limit mode with the configured value (for example 2 MiB) to get three files: limit minus 1 byte, the exact limit and limit plus 1 byte. The first two should pass and the third should be rejected. Remember the limit can sit in more than one layer: nginx rejects bodies above client_max_body_size with 413 (default 1m), and PHP uses upload_max_filesize (default 2M) and post_max_size (default 8M).

Question 6

How does the PNG reach the exact size?

Accepted Answer

With an extra chunk named duMy placed before IEND. In the PNG specification a lowercase first letter marks the chunk as ancillary (it may be ignored), a lowercase second letter as private, the third letter must be uppercase and a lowercase fourth letter means safe to copy. Decoders that do not know the chunk simply skip it. Its CRC is computed like any other chunk's.

Question 7

Can I generate a deliberately corrupted file?

Accepted Answer

Yes, in Format options. Truncated removes the second half of the valid file, which breaks PDF, ZIP and JSON. Swapped magic bytes keeps the size and replaces the first 4 bytes with DE AD BE EF, so the file is no longer recognized as PDF, PNG, JPG or ZIP. Use it to check that your system handles the error instead of crashing.

Question 8

Does the WAV have the exact duration I want?

Accepted Answer

Duration comes from size: (size minus the 44-byte header) divided by sample rate x channels x 2 bytes. At 44,100 Hz mono 16-bit that is 88,200 bytes per second, so 5 seconds need 441,044 bytes. A field lets you enter seconds and apply the size. If the size does not close a whole number of samples, the last partial frame is ignored by players and the tool warns you.

Question 9

Is the CSV and JSON data real?

Accepted Answer

No. Names, e-mails (always on example.com, example.org or example.net), cities, amounts and dates are fictitious combinations. With the same seed and size the file comes out identical, which helps repeatable tests. The last column, note, is filler text that closes the exact size.

Question 10

Do my files go to any server?

Accepted Answer

No. Generation happens in the browser, in chunks, and the download uses a local Blob. Files of hundreds of MB use tab and system memory: close other tabs and download one at a time. On phones and tablets memory is usually smaller, so the tool already lowers the cap on touch screens.

Dummy File Generator