So I’ve been mass-upgrading a handful of Go services at work this week, and I stumbled onto something that made me mass-upgrade all of them: the go fix tool in Go 1.26 now ships with 24 built-in modernizers, and honestly it’s kind of magical.

If you haven’t seen it yet, running it is dead simple:

$ go fix -fix modernize ./...

That’s it. One command, and it sweeps through your entire module looking for outdated patterns it can safely replace with modern equivalents. No config files, no third-party linters — it’s right there in the toolchain.

Here’s the kind of stuff it catches. Say you’ve got code like this scattered around:

func process(data map[string]interface{}) {
    var result []string
    for i := 0; i < len(data); i++ {
        if strings.Index(name, "@") != -1 {
            // ...
        }
    }
}

After go fix, you get:

func process(data map[string]any) {
    var result []string
    for i := range len(data) {
        if strings.Contains(name, "@") {
            // ...
        }
    }
}

interface{} → any. Integer range loops using range len(...) (Go 1.22+). strings.Index != -1 replaced with strings.Contains. All automatic, all correct.

A few of my favorite fixers from the 24 built-in ones:

  • efaceany — Replaces interface{} with any everywhere. This one alone touched 200+ files in our biggest service.
  • stringscutprefix — Spots the classic “check HasPrefix then TrimPrefix” pattern and collapses it into strings.CutPrefix.
  • sortslice — Swaps sort.Slice calls for slices.SortFunc from the newer slices package.
  • mapsloop — Replaces manual map-to-slice loops with maps.Keys or maps.Values.
  • rangeint — Converts for i := 0; i < n; i++ to for i := range n.

What I really appreciate is that each fixer targets a specific Go version, so it only applies changes your go.mod’s go directive supports. Bumping from go 1.21 to go 1.26 in go.mod and then running go fix is a surprisingly satisfying workflow.

I ran it across six services this week. Zero test failures. The diffs were huge but entirely mechanical — great PRs to review because there’s nothing subtle going on. If you’ve got any Go code that predates 1.22, give it a shot. You’ll be surprised how much cleaner things look on the other side.