A regex engine built from scratch using python, and a TUI using Textual!
Ever part of this including stuff like the lexer, parser, the ast, and the backtracking were written by hand :)
pip install regecks
regeckss
Requires uv
git clone https://github.com/kashsuks/regecks
cd regecks
uv syncc
| Key |
Action |
| Tab |
Move between pattern and test string fields |
| Ctrl+R |
Run match manually |
| Ctrl+C |
Quit |
Matches get updated live
| Pattern |
Match |
| a |
The character a |
| abc |
The string abc exactly |
| Pattern |
Match |
| . |
Any single character except newline |
All quantifiers are greedy and therefore consume as much as possible.
| Pattern |
Match |
| a* |
Zero or more a |
| a+ |
One or more a |
| a? |
Zero or one a |
| a{3} |
Exactly 3 a |
| a{2,} |
2 or more a |
| a{2,4} |
Between 2 and 4 a (inclusive) |
| Pattern |
Match |
| ^abc |
abc only at the start of the string |
| abc$ |
abc only at the end of the string |
| \b |
Word boundary (between \w and \W) |
| \B |
Non-word boundary |
| Pattern |
Match |
| [abc] |
Any one of a, b, or c |
| [a-z] |
Any lowercase letter |
| [A-Z0-9] |
Any uppercase letter or digit |
| [^abc] |
Any character except a, b, c |
| [^0-9] |
Any non-digit |
| Pattern |
Match |
| \d |
Any digit [0-9] |
| \D |
Any non-digit |
| \w |
Any word character [a-zA-Z0-9_] |
| \W |
Any non-word character |
| \s |
Any whitespace (space, tab, newline, etc) |
| \S |
Any non-whitespace |
| \n |
Newline |
| \t |
Tab |
| \n |
Literal dot (escaping special chars) |
| Pattern |
Match |
| cat|dog |
Either cat or dog |
| foo|bar|baz |
Any of the three |
| Pattern |
Match |
| (abc) |
abc, captured as group 1 |
| (a)(b) |
ab, with a as group 1 and b as group 2 |
| (?:abc) |
abc, not captured |
| (?Pabc) |
abc, captured as named group name |
| Pattern |
Match |
| (?iabc) |
Match abc case-insensitively and matches ABC, abc, etc. |
The flags wrap everything that follows it in a pattern
These are zero-width assertions meaning they check for a condition without consuming characters.
Claude code was used in this project for debugging the ui and parts of the lexer
