goconst

Find repeated strings that could be replaced by a constant.

Motivation

There are obvious benefits to using constants instead of repeating strings, mostly to ease maintenance. Cannot argue against changing a single constant versus many strings.

While this could be considered a beginner mistake, across time, multiple packages and large codebases, some repetition could have slipped in.

How it works

goconst detects string (and optionally number) literals that appear multiple times and could be replaced by a constant.

A few things to keep in mind:

• Exact literal matching — goconst compares complete, unquoted literal values. Repeated substrings inside larger strings are not detected (e.g., a shared prefix across two different string literals will not be reported).
• const declarations are skipped by default — constant values are only analyzed when -match-constant (match strings against existing constants) or -find-duplicates (find constants sharing the same value) is enabled.
• String length is measured in runes, not bytes, so multi-byte Unicode characters are counted correctly against -min-length.

Get Started

$ go install github.com/jgautheron/goconst/cmd/goconst@latest
$ goconst ./...

Usage

Usage:

  goconst ARGS <directory> [<directory>...]

Flags:

  -ignore                     exclude files matching the given regular expression
  -ignore-strings             exclude strings matching the given regular expression
  -ignore-tests               exclude tests from the search (default: true)
  -min-occurrences            report from how many occurrences (default: 2)
  -min-length                 only report strings with the minimum given length (default: 3)
  -match-constant             look for existing constants matching the strings
  -find-duplicates            look for constants with identical values
  -eval-const-expr            enable evaluation of constant expressions (e.g., Prefix + "suffix")
  -ignore-calls               ignore string literals in calls to these functions (comma separated)
  -ignore-composite-literals  ignore string literals inside composite literals
  -ignore-map-keys            ignore string literals used as map keys
  -numbers                    search also for duplicated numbers
  -min                        minimum value, only works with -numbers
  -max                        maximum value, only works with -numbers
  -output                     output formatting (text or json)
  -set-exit-status            Set exit status to 2 if any issues are found
  -grouped                    print single line per match, only works with -output text

Examples:

  goconst ./...
  goconst -ignore "yacc|\.pb\." $GOPATH/src/github.com/cockroachdb/cockroach/...
  goconst -min-occurrences 3 -output json $GOPATH/src/github.com/cockroachdb/cockroach
  goconst -numbers -min 60 -max 512 .
  goconst -min-occurrences 5 $(go list -m -f '{{.Dir}}')
  goconst -eval-const-expr -match-constant . # Matches constant expressions like Prefix + "suffix"
  goconst -ignore-calls slog.Info,slog.Warn,fmt.Errorf ./... # Ignore strings in logging/error calls

Development

Running Tests

The project includes a comprehensive test suite. To run the tests:

# Run all tests
go test ./...

# Run tests with verbose output
go test -v ./...

# Run tests with race detector
go test -race ./...

# Run benchmarks
go test -bench=. ./...

# Check test coverage
go test -cover ./...

Contributing

Contributions are welcome! Before submitting a PR:

1. Make sure all tests pass
2. Add tests for new functionality
3. Ensure your code passes linting checks
4. Update documentation as needed

Other static analysis tools

• gogetimports: Get a JSON-formatted list of imports.
• usedexports: Find exported variables that could be unexported.

License

MIT