Offline Regex Tester & Network Log Matcher
Test regular expressions with real-time match highlighting, capture-group extraction tables, and one-click presets for IPv4, CIDR, MAC addresses, and Nginx access logs.
Match Highlights & Extracted Capture Groups (0 Matches)
| Match # | Index | Full Match ($0) |
Capture Groups ($1, $2...) |
|---|
Writing Safe, Fast Regular Expressions for Log Parsing & WAF Rules
Regular expressions power log ingestion pipelines (Fluent Bit, Vector, Logstash Grok), Prometheus relabeling configs, Nginx location ~ routing blocks, and Web Application Firewall (WAF) inspection rules. Testing complex capture groups offline inside your browser ensures production firewall logs, customer IP addresses, and internal hostnames never leave your workstation.
When deploying regexes in high-throughput proxies or server-side validators, guard against Catastrophic Backtracking (ReDoS) caused by nested ambiguous quantifiers such as (a+)+ or overlapping alternations like (.*a.*)+. Prefer bounded quantifiers (\d{1,3}), negated character classes ([^"\s]+), and non-capturing groups ((?:...)) whenever backreferences are unnecessary.
Note that while JavaScript, Python, and PCRE support lookaheads and backreferences, high-speed engines used by Cloudflare WAF, Envoy, Go, and Prometheus rely on linear-time RE2 syntax—keeping patterns free of backreferences ensures seamless portability across modern cloud-native infrastructure.