Regex Test MCP tool

Test a JavaScript regular expression against input text. Returns every match (up to 1000) with its index, its numbered capture groups (captures: $1, $2, …, null for a group that did not take part) and its named groups. With replace, also returns the text after String.prototype.replace, which understands $1, $<name>, $&, $` , $' and $$ and replaces every match only when the g flag is set. Input past 50,000 characters is cut and marked truncated. Patterns with nested quantifiers are refused.