Name checker: folder and file names
Paste a list of folder or file names, one per line, and see which ones have spaces, characters some computers reject, dates in a different form from the one you chose, or names that are long or say "final". Nothing you paste leaves this browser.
Use it before you rename a batch of folders, or on the folder names you plan to create: type them or paste them, one per line. The rules come from Folders and file names, where each one is explained.
What it checks, and why
| Flag | Why | Source |
|---|---|---|
| Spaces | Some programs and web addresses break a name at a space. | National Archives Bulletin 2015-04, Appendix B; Harvard Medical School |
| Characters other than letters, numbers, hyphen and underscore | The National Archives' transfer rule allows only these, plus one period before the extension. | National Archives Appendix B |
| Characters Windows cannot save: < > : " / \ | ? * | A copy to a Windows computer or a drive formatted for Windows stops at them. A time such as 14:30 cannot go in a name. | Microsoft, Naming Files, Paths, and Namespaces |
| Names Windows reserves (CON, PRN, AUX, NUL, COM1 to COM9, LPT1 to LPT9), and a name ending in a period or space | Windows refuses them, even with an extension. | Microsoft |
| More than one period | Programs read the part after the last period as the file type. | National Archives Appendix B |
| A date in the other ISO form, or a date that does not start with the year | Both YYYY-MM-DD and YYYYMMDD are valid ISO 8601 dates; mixing them, or using 7-4-26, breaks the sort. | W3C Date and Time Formats; Harvard |
| Over 50 characters | Harvard suggests 40 to 50; long names hit path limits sooner. A look, not a rule. | Harvard |
| "final", "new", "latest" | They stop being true the next time something changes. | UK Data Service; Harvard |
Assumptions behind the checks
- Safe characters are letters, numbers, hyphens and underscores, plus one period before an extension, following the National Archives' file-naming appendix and the university guides in Folders and file names. Convention
- The characters and names Windows reserves (\ / : * ? " < > | and names such as CON, PRN, AUX, NUL, COM1 and LPT1) are flagged because a Windows computer cannot save them. Product-specific
- Fifty characters is Harvard Medical School's upper figure for a file name. It is a convention, not a limit; a longer name is flagged only so you can look at it.
- "Final", "new" and "latest" are flagged because they stop being true; the UK Data Service and Harvard both advise against them.
- A camera's own file name (IMG_4821.HEIC, DSC_0042.NEF) passes; this manual leaves camera names as they are, so the checker does not ask for a date in them.
- The checker reads only what you paste. It does not look at your files, and nothing is sent anywhere.
The checker reads names, not files. It cannot tell whether a renamed file has lost its partner (a raw file's JPEG, a Live Photo's video, a caption sidecar), and it does not check the full path length, which depends on the drive and the folders above. Do not rename files inside a photo app's library; the app manages those.