regex-builder

Name: regex-builder
Author: girijashankarj

27stars3forks

How to install regex-builder?

girijashankarj/cursor-handbook/regex-builder

$npx -y skills add girijashankarj/cursor-handbook --skill regex-builder

Installs into the current project.

Summary

Build, explain, and test regular expressions step-by-step with plain-English breakdowns. Use when the user asks to create, debug, or explain a regex pattern.

Files · 1

View on GitHub

SKILL.md

1	# Skill: Regex Builder
2
3	Construct and explain regular expressions incrementally with test cases and plain-English documentation.
4
5	## Trigger
6	When the user asks to build, create, explain, debug, or optimize a regular expression.
7
8	## Prerequisites
9	- [ ] Target pattern or matching criteria described
10	- [ ] Sample inputs (should match and should NOT match)
11	- [ ] Target language/flavor (JavaScript, Python, Go, PCRE)
12
13	## Steps
14
15	### Step 1: Clarify Requirements
16	- [ ] What should the regex match? (exact description)
17	- [ ] What should it NOT match? (edge cases)
18	- [ ] Capture groups needed? (which parts to extract)
19	- [ ] Flags needed? (case-insensitive, multiline, global, dotall)
20	- [ ] Performance constraints? (large input, many matches)
21
22	### Step 2: Build Incrementally
23
24	Start with the simplest pattern that matches, then refine:
25
26	1. Literal match — match the exact string first
27	2. Character classes — generalize with `[a-z]`, `\d`, `\w`
28	3. Quantifiers — add `+`, `*`, `{n,m}` for repetition
29	4. Anchors — add `^`, `$` for position
30	5. Groups — add `()` for captures, `(?:)` for non-capturing
31	6. Alternation — add `\|` for OR logic
32	7. Lookahead/behind — add `(?=)`, `(?<=)` for assertions
33
34	### Step 3: Document the Pattern
35
36	Break down every component:
37
38	```
39	Pattern: ^(?<protocol>https?):\/\/(?<domain>[a-zA-Z0-9.-]+)(?::(?<port>\d{1,5}))?(?<path>\/[^\s?#])?(?:\?(?<query>[^\s#]))?(?:#(?<fragment>\S*))?$
40
41	Breakdown:
42	^ Start of string
43	(?<protocol>https?) Capture "http" or "https"
44	:\/\/ Literal "://"
45	(?<domain>[a-zA-Z0-9.-]+) Capture domain name
46	(?::(?<port>\d{1,5}))? Optional port number (1-5 digits)
47	(?<path>\/[^\s?#]*)? Optional path starting with /
48	(?:\?(?<query>[^\s#]*))? Optional query string after ?
49	(?:#(?<fragment>\S*))? Optional fragment after #
50	$ End of string
51	```
52
53	### Step 4: Create Test Cases
54
55	```
56	✅ Should match:
57	"https://example.com" → protocol=https, domain=example.com
58	"http://api.example.com:8080/v1/users" → port=8080, path=/v1/users
59	"https://example.com/search?q=test#top" → query=q=test, fragment=top
60
61	❌ Should NOT match:
62	"ftp://example.com" → wrong protocol
63	"not-a-url" → no protocol
64	"" → empty string
65	```
66
67	### Step 5: Validate Edge Cases
68	- [ ] Empty input
69	- [ ] Very long input (ReDoS risk)
70	- [ ] Unicode characters
71	- [ ] Special regex characters in input (`.`, `*`, `+`, `?`)
72	- [ ] Newlines and whitespace
73
74	### Step 6: Check for ReDoS Vulnerability
75	Avoid catastrophic backtracking patterns:
76	- Dangerous: `(a+)+`, `(a\|a)+`, `(a+b?)+` on non-matching input
77	- Safe: Use atomic groups, possessive quantifiers, or rewrite
78	- If pattern has nested quantifiers on overlapping character classes → flag as risky
79
80	### Step 7: Provide Language-Specific Usage
81
82	JavaScript:
83	```javascript
84	const pattern = /^https?:\/\/[a-zA-Z0-9.-]+/;
85	const match = url.match(pattern);
86	const isValid = pattern.test(url);
87	```
88
89	Python:
90	```python
91	import re
92	pattern = re.compile(r'^https?://[a-zA-Z0-9.-]+')
93	match = pattern.match(url)
94	is_valid = bool(pattern.match(url))
95	```
96
97	Go:
98	```go
99	pattern := regexp.MustCompile(`^https?://[a-zA-Z0-9.-]+`)
100	match := pattern.FindString(url)
101	isValid := pattern.MatchString(url)
102	```
103
104	## Common Patterns Reference
105
106	\| Need \| Pattern \| Notes \|
107	\|------\|---------\|-------\|
108	\| Email (basic) \| `^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$` \| Not RFC-compliant, covers 99% \|
109	\| UUID \| `^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$` \| Case-insensitive flag \|
110	\| ISO date \| `^\d{4}-\d{2}-\d{2}$` \| Doesn't validate ranges \|
111	\| Semantic version \| `^v?\d+\.\d+\.\d+(-[a-zA-Z0-9.]+)?$` \| Optional `v` prefix \|
112	\| IP address (v4) \| `^(\d{1,3}\.){3}\d{1,3}$` \| Doesn't validate 0–255 \|
113	\| Slug \| `^[a-z0-9]+(-[a-z0-9]+)*$` \| Lowercase with hyphens \|
114
115	## Rules
116	- ALWAYS explain each component in plain English
117	- ALWAYS provide test cases (match and non-match)
118	- ALWAYS check for ReDoS vulnerability on complex patterns
119	- NEVER use regex for HTML parsing — use a proper parser
120	- Prefer readability over cleverness — comment complex patterns
121	- Use named capture groups when extracting data
122	- Mention flavor differences (JS vs Python vs Go) when they matter
123
124	## Completion
125	Working regex with plain-English breakdown, test cases, language-specific usage, and ReDoS safety check.
126
127	## If a Step Fails
128	- Can't express requirement in regex: Consider a parser or multi-step validation instead
129	- ReDoS risk detected: Rewrite with non-overlapping character classes or use a timeout
130	- Flavor mismatch: Note which features are unavailable (e.g., lookbehind in older JS)
131	- Too complex: Split into multiple simpler patterns applied sequentia

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regex-builder

27stars3forks

View on GitHub

How to install regex-builder?

girijashankarj/cursor-handbook/regex-builder

$npx -y skills add girijashankarj/cursor-handbook --skill regex-builder

Installs into the current project.

Summary

Build, explain, and test regular expressions step-by-step with plain-English breakdowns. Use when the user asks to create, debug, or explain a regex pattern.

Files · 1

View on GitHub

SKILL.md

1	# Skill: Regex Builder
2
3	Construct and explain regular expressions incrementally with test cases and plain-English documentation.
4
5	## Trigger
6	When the user asks to build, create, explain, debug, or optimize a regular expression.
7
8	## Prerequisites
9	- [ ] Target pattern or matching criteria described
10	- [ ] Sample inputs (should match and should NOT match)
11	- [ ] Target language/flavor (JavaScript, Python, Go, PCRE)
12
13	## Steps
14
15	### Step 1: Clarify Requirements
16	- [ ] What should the regex match? (exact description)
17	- [ ] What should it NOT match? (edge cases)
18	- [ ] Capture groups needed? (which parts to extract)
19	- [ ] Flags needed? (case-insensitive, multiline, global, dotall)
20	- [ ] Performance constraints? (large input, many matches)
21
22	### Step 2: Build Incrementally
23
24	Start with the simplest pattern that matches, then refine:
25
26	1. Literal match — match the exact string first
27	2. Character classes — generalize with `[a-z]`, `\d`, `\w`
28	3. Quantifiers — add `+`, `*`, `{n,m}` for repetition
29	4. Anchors — add `^`, `$` for position
30	5. Groups — add `()` for captures, `(?:)` for non-capturing
31	6. Alternation — add `\|` for OR logic
32	7. Lookahead/behind — add `(?=)`, `(?<=)` for assertions
33
34	### Step 3: Document the Pattern
35
36	Break down every component:
37
38	```
39	Pattern: ^(?<protocol>https?):\/\/(?<domain>[a-zA-Z0-9.-]+)(?::(?<port>\d{1,5}))?(?<path>\/[^\s?#])?(?:\?(?<query>[^\s#]))?(?:#(?<fragment>\S*))?$
40
41	Breakdown:
42	^ Start of string
43	(?<protocol>https?) Capture "http" or "https"
44	:\/\/ Literal "://"
45	(?<domain>[a-zA-Z0-9.-]+) Capture domain name
46	(?::(?<port>\d{1,5}))? Optional port number (1-5 digits)
47	(?<path>\/[^\s?#]*)? Optional path starting with /
48	(?:\?(?<query>[^\s#]*))? Optional query string after ?
49	(?:#(?<fragment>\S*))? Optional fragment after #
50	$ End of string
51	```
52
53	### Step 4: Create Test Cases
54
55	```
56	✅ Should match:
57	"https://example.com" → protocol=https, domain=example.com
58	"http://api.example.com:8080/v1/users" → port=8080, path=/v1/users
59	"https://example.com/search?q=test#top" → query=q=test, fragment=top
60
61	❌ Should NOT match:
62	"ftp://example.com" → wrong protocol
63	"not-a-url" → no protocol
64	"" → empty string
65	```
66
67	### Step 5: Validate Edge Cases
68	- [ ] Empty input
69	- [ ] Very long input (ReDoS risk)
70	- [ ] Unicode characters
71	- [ ] Special regex characters in input (`.`, `*`, `+`, `?`)
72	- [ ] Newlines and whitespace
73
74	### Step 6: Check for ReDoS Vulnerability
75	Avoid catastrophic backtracking patterns:
76	- Dangerous: `(a+)+`, `(a\|a)+`, `(a+b?)+` on non-matching input
77	- Safe: Use atomic groups, possessive quantifiers, or rewrite
78	- If pattern has nested quantifiers on overlapping character classes → flag as risky
79
80	### Step 7: Provide Language-Specific Usage
81
82	JavaScript:
83	```javascript
84	const pattern = /^https?:\/\/[a-zA-Z0-9.-]+/;
85	const match = url.match(pattern);
86	const isValid = pattern.test(url);
87	```
88
89	Python:
90	```python
91	import re
92	pattern = re.compile(r'^https?://[a-zA-Z0-9.-]+')
93	match = pattern.match(url)
94	is_valid = bool(pattern.match(url))
95	```
96
97	Go:
98	```go
99	pattern := regexp.MustCompile(`^https?://[a-zA-Z0-9.-]+`)
100	match := pattern.FindString(url)
101	isValid := pattern.MatchString(url)
102	```
103
104	## Common Patterns Reference
105
106	\| Need \| Pattern \| Notes \|
107	\|------\|---------\|-------\|
108	\| Email (basic) \| `^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$` \| Not RFC-compliant, covers 99% \|
109	\| UUID \| `^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$` \| Case-insensitive flag \|
110	\| ISO date \| `^\d{4}-\d{2}-\d{2}$` \| Doesn't validate ranges \|
111	\| Semantic version \| `^v?\d+\.\d+\.\d+(-[a-zA-Z0-9.]+)?$` \| Optional `v` prefix \|
112	\| IP address (v4) \| `^(\d{1,3}\.){3}\d{1,3}$` \| Doesn't validate 0–255 \|
113	\| Slug \| `^[a-z0-9]+(-[a-z0-9]+)*$` \| Lowercase with hyphens \|
114
115	## Rules
116	- ALWAYS explain each component in plain English
117	- ALWAYS provide test cases (match and non-match)
118	- ALWAYS check for ReDoS vulnerability on complex patterns
119	- NEVER use regex for HTML parsing — use a proper parser
120	- Prefer readability over cleverness — comment complex patterns
121	- Use named capture groups when extracting data
122	- Mention flavor differences (JS vs Python vs Go) when they matter
123
124	## Completion
125	Working regex with plain-English breakdown, test cases, language-specific usage, and ReDoS safety check.
126
127	## If a Step Fails
128	- Can't express requirement in regex: Consider a parser or multi-step validation instead
129	- ReDoS risk detected: Rewrite with non-overlapping character classes or use a timeout
130	- Flavor mismatch: Note which features are unavailable (e.g., lookbehind in older JS)
131	- Too complex: Split into multiple simpler patterns applied sequentia

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6 picks

Type