What it does
Paste an iRule; the linter flags a small set of high-confidence, F5-documented performance and correctness anti-patterns, line by line, each with a severity, the offending token, why it matters, and the fix. It is a static scanner (no Tcl parser, no execution), so it deliberately covers only patterns a line scan can catch reliably and with few false positives. It is not a substitute for measurement: pair it with the iRules Runtime Calculator, which reads real timing statistics, for the actual cost of a rule. Everything runs locally.
What it flags
Global-namespace variables ($::x, set ::x, the global keyword) are flagged HIGH. F5's validator catches the global keyword as of v10 and demotes the virtual server to a single TMM instance (CMP demotion), so one processor handles all of that virtual's connections; global variables have been deprecated since v10. The obsolete $::datagroup form is worse still: on version 11 and later, accessing a data group that way raises a TCL runtime error and sends a reset to the client. The fix is the CMP-safe static:: namespace for shared constants, ordinary local variables for per-connection data, or the class command for data groups.
expr without braces is a WARNING. Tcl substitutes and re-parses the unbraced form, and can double-substitute; bracing the expression lets the bytecode compiler optimize it. The fix is expr { ... }.
matchclass / findclass are INFO. Both were deprecated in v10 in favor of the class command, which F5 describes as offering better functionality and performance. The fix is class match / class search.
regexp / regsub are INFO. Regular expressions cost materially more than fixed string work; when the match is a prefix, suffix, exact value, or simple glob, string, scan, switch -glob, or class are cheaper.
What it deliberately does not flag
static:: variables (CMP-safe), class match / class search, and braced expr are correct and pass clean. Persistence, tables, and the session command are CMP-compatible on modern versions, so they are not treated as CMP problems. Full-line comments are skipped.