Use regular expressions for batch file renaming

Regex works best when filenames are consistent. Match only the part you intend to change, and keep the replacement readable. A narrow pattern is easier to review than a clever pattern that tries to solve every filename at once.

Use capture groups when you need to keep useful parts and rearrange them in a new order. In Rename.Tools, the replacement can use $1, $2, and later groups to put captured pieces back into the new name.

Before writing the regex, describe the filename in plain language: where is the date, where is the title, where is the episode code, and which parts should be deleted. That description often becomes the pattern.

These patterns are good starting points. Preview them on a small file set before applying them to a folder with thousands of files. If one pattern feels fragile, split the workflow into a regex rule plus a simple Find & Replace cleanup rule.

Keep the Flags field intentional. Use i for case-insensitive matching, g when you want every occurrence replaced, and avoid m unless you are working with multi-line text pasted into filenames.

Avoid overly broad patterns like .* unless you really mean to replace everything. If a replacement produces empty names, duplicate names, or removes more text than expected, stop and narrow the match.

When the regex rule is hard to reason about, split the workflow into two or three simpler rules. The preview will be easier to audit, and future you will understand the preset more quickly.

Regex does not need to be the first rule. Often the clearest workflow is to clean obvious text with Find & Replace, use regex for the structural transformation, then apply Case/Style or Sequence as the final polish.

When a regex does not work, do not immediately make it more complex. First check whether the pattern is matching the right text at all. A good debugging trick is to replace with a visible marker such as MATCH_$1 so you can see what was captured.

Then restore the real replacement once the captured groups are correct. This workflow is slower for one filename, but much faster for a folder with hundreds of files.

Regex is powerful, but it is not always the clearest tool. If you only need to replace one literal word, use Find & Replace. If you only need numbering, use Sequence. If you need case conversion, use Case/Style.

The best rule chain is often a combination: simple rules for simple edits, regex only for the structural part, and a final preview pass to verify the result. This keeps presets easier to maintain and safer for future batches.