Filename & file compatibility, at a glance

What breaks when files move between 🪟 Windows, 🍎 macOS and 🐧 Linux — characters, reserved names, path separators, zero-byte files and more. Scan the matrix, then dig into any row.

✓ Allowed ✗ Forbidden / breaks ! Silently changed / risky
Rule 🪟Windows 🍎macOS 🐧Linux
Special chars : * ? " < > | ✗forbidden !avoid : ✓allowed
Backslash \ in a name ✗path separator ✓ordinary char ✓ordinary char
Reserved names CON NUL ✗forbidden ✓allowed ✓allowed
Case-sensitive names ✗merges ✗merges (default) ✓distinct
Unicode NFC = NFD !bytes as-is !stores NFD !bytes as-is
Trailing . or space ✗stripped ✓kept ✓kept
Path length !260 default ✓1024 ✓4096
Zero-byte file ✓"0 KB" ✓"Zero bytes" ✓0
Text line endings !CRLF !LF !LF

Forbidden characters

Windows rejects these outright. Linux allows almost anything.

<>:"/\|?*
🪟
Windows
✗ all 9
🍎
macOS
! / and :
🐧
Linux
✓ only /

Trap: report:2024.txt is legal on Linux, impossible on Windows — sync skips it.

Try: question?name.txt · double"quote.txt

Path separators: / vs \

The single biggest cross-platform path bug.

🪟
Windows
\ (also /)
🍎
macOS
/ only
🐧
Linux
/ only

Trap: on Linux, folder\file is one filename containing a backslash. Move it to Windows and it becomes a folder ➜ file path — or fails. Web URLs are always /.

Try: backslash\name.txt

Reserved device names

Windows keeps legacy device names — even with an extension.

CONPRNAUXNULCOM1–9LPT1–9
🪟
Windows
✗ forbidden
🍎
macOS
✓ fine
🐧
Linux
✓ fine

Trap: CON.txt and nul.log can't be created or extracted on Windows.

Try: CON.txt · NUL.txt

Case sensitivity

Are File.txt and file.txt the same file?

🪟
Windows
Same → merge
🍎
macOS
Same (default)
🐧
Linux
Two files

Trap: a repo with README.md + Readme.md loses one file when cloned on Windows/Mac.

Unicode normalization

café can be 4 code points (NFC) or 5 (NFD). Same look, different bytes.

🪟
Windows
as-is (NFC)
🍎
macOS
stores NFD
🐧
Linux
as-is (NFC)

Trap: a Mac-saved café.txt won't match the same name typed on Windows — "file not found" for a name you can see.

Try: nfc-café.txt vs nfd-café.txt

Trailing dots & spaces

Windows silently strips a trailing . or space.

🪟
Windows
✗ stripped
🍎
macOS
✓ kept
🐧
Linux
✓ kept

Trap: report. becomes report — two files collide into one.

Try: trailing-dot.txt.

Length limits

Per-name and full-path caps.

🪟
Windows
260 path*
🍎
macOS
1024 path
🐧
Linux
4096 path

Names: 255 units (Win/Mac) or 255 bytes (Linux — so ~63 emoji). *Windows lifts 260 only with long-path mode.

Try: a 204-char name

Zero-byte files

A file with no content is valid everywhere — but shown and handled differently.

🪟 Explorer
empty.txt
0 KB
🍎 Finder
empty.txt
Zero bytes
🐧 ls -l
-rw-r--r-- 1 0 empty.txt

Trap: upload validators that check MIME but not size > 0 accept empty files; some sync clients skip them; Git needs an explicit add. Used deliberately as markers (.gitkeep).

Try: 0b.bin (exactly 0 bytes)

Text line endings

Same text, different bytes per platform.

🪟
Windows
\r\n CRLF
🍎
macOS
\n LF
🐧
Linux
\n LF

Trap: breaks diffs, checksums and line-by-line parsers. Classic Mac used bare \r (CR).

Try: crlf.txt vs lf.txt

Cloud sync services add their own rules

OneDrive, Dropbox and Drive apply the strictest (Windows-style) rules on every platform, plus extra reserved names and path caps.

☁️
OneDrive / SharePoint
Blocks " * : < > ? / \ |, .lock, CON…LPT9, ~$…, leading/trailing spaces, ~400-char paths
📦
Dropbox
Blocks / \ < > : " | ? *, .dropbox, desktop.ini; case-insensitive; no trailing spaces/dots
🗂️
Google Drive
Permissive storage, but case- & normalization-insensitive matching can conflict on the desktop client

Safe-everywhere rule: use only A–Z a–z 0–9 . _ -, no leading/trailing dots or spaces, avoid Windows reserved names, keep paths under ~255 chars, normalize Unicode to NFC.

Prove your app handles these

Every rule above has a matching test file in the catalog — upload one and confirm your app fails gracefully, not silently.

→ Browse the filename & encoding test files