Every file name is a small decision. Make that decision well once and you don't have to think about it again. Make it badly and you spend the rest of the project's life searching for things, misidentifying versions, and manually cleaning up names that should have been right from the start. Filename — Batch File Renaming is a Mac app built for the people who care about this kind of discipline: photographers, designers, developers, and anyone managing structured file collections.
The 30-second rename workflow
Here's the core loop: open Filename, drag in a folder of files, build a rename rule, verify the preview, apply. For a folder of 200 vacation photos named DSC_0001.jpg through DSC_0200.jpg, the rename to Tokyo_2025_001.jpg through Tokyo_2025_200.jpg takes about 30 seconds to set up and 2 seconds to execute. The preview updates live, so you know exactly what every file will be called before you commit.
Rule types that cover 95% of rename jobs
Sequential numbering: Add 001, 002, 003... to any position in the name with configurable padding and start number. Useful for photos, design revisions, chapter files.
Date insertion: Pull the file creation date, modification date, or EXIF date (for photos) and insert it in your preferred format (YYYY-MM-DD, YYYYMMDD, etc.). This is the most reliable way to create date-organized archives.
Text replacement: Replace any substring with another. Works on multiple files simultaneously. Remove a common prefix, fix a typo that appears in 40 filenames, strip download IDs from service-generated names.
Case conversion: Uppercase, lowercase, title case, or sentence case across all selected files. Normalize an inconsistent archive in one click.
Custom prefix / suffix: Add a project code, client name, or version tag to all files in a batch.
Presets for recurring workflows
The rename setup you use for client photo deliveries is probably the same every time. Same for design export cleanup, for podcast episode naming, for weekly report files. Save any rule combination as a named preset. When you need it again, open Filename, select the preset, drop in the files, apply. The configuration work happens once.
Undo: the safety net
Batch renaming 300 files and discovering you used the wrong format is a nightmare without undo. Filename stores the full original-to-new mapping until you clear it, enabling single-click undo of an entire batch operation regardless of file count. Rename, verify the result looks right, then dismiss the undo history. If something's wrong, undo everything and fix the rule.
File extension handling
By default, rename rules apply to the filename without touching the extension — so your .jpg, .png, and .pdf files keep their extensions regardless of what the rule does to the base name. You can also explicitly change extensions when needed (converting a batch of .jpeg files to .jpg notation, for example).
Filename — Batch File Renaming is $9.99 one-time on the Mac App Store, requires macOS 13 Ventura.