Regex101 has real depth this doesn't try to match: a large, established Community Pattern Library, a Pro tier with benchmarking and a substitution pipeline, and support for more regex flavors than are offered here. If you already have a pattern and want to test, debug, and benchmark it across flavors, regex101 is the more mature tool.
The actual difference: regex101 explains a pattern you've already written — it doesn't write one for you. This tool generates a pattern from a plain-English description first, then lets you test and refine it. And the features that map to regex101's paid Pro tier (pattern optimization, AI explanation, test generation) are free here, rate-limited rather than paywalled.
Already have a pattern, want deep debugging or a huge community library to draw from: regex101. Don't want to write the regex by hand at all: this tool.