Golang -json Flag

Go 1.24 has added a new -json flag to go build, go install & go test. This makes it easier to parse output. I’ve added a few examples to this post.

go build

#

package main

import (
  "fmt"
)

func main() {
  fmt.Prrintln("Hello World")
}

go build will output:

# github.com/alrayyes/golanghelloworld
./main.go:8:6: undefined: fmt.Prrintln

go build -json will output:

{"ImportPath":"github.com/alrayyes/golanghelloworld","Action":"build-output","Output":"# github.com/alrayyes/golanghelloworld\n"}
{"ImportPath":"github.com/alrayyes/golanghelloworld","Action":"build-output","Output":"./main.go:8:6: undefined: fmt.Prrintln\n"}
{"ImportPath":"github.com/alrayyes/golanghelloworld","Action":"build-fail"}

go install

#

package main

import (
  "fmt"
)

func main() {
  fmt.Prrintln("Hello World")
}

go install will output:

# github.com/alrayyes/golanghelloworld
./main.go:8:6: undefined: fmt.Printlln

go install -json will output:

{"ImportPath":"github.com/alrayyes/golanghelloworld","Action":"build-output","Output":"# github.com/alrayyes/golanghelloworld\n"}
{"ImportPath":"github.com/alrayyes/golanghelloworld","Action":"build-output","Output":"./main.go:8:6: undefined: fmt.Printlln\n"}
{"ImportPath":"github.com/alrayyes/golanghelloworld","Action":"build-fail"}

go test

#

package main

import (
  "bytes"
  "fmt"
  "github.com/stretchr/testify/assert"
  "io"
  "os"
  "testing"
)

func main() {
  fmt.Println("Hello World")
}

func TestCmdOutput(t *testing.T) {
  oldStdout := os.Stdout

  r, w, _ := os.Pipe()
  os.Stdout = w

  main()

  _ = w.Close()

  os.Stdout = oldStdout

  var buf bytes.Buffer
  _, _ = io.Copy(&buf, r)
  got := buf.String()

  want := "Hello World\n"

  assert.Equal(t, want, got)
}

go test will output:

PASS
ok      github.com/alrayyes/golanghelloworld    0.002s

go build -json will output:

{"Time":"2025-02-14T17:39:12.407851295+01:00","Action":"start","Package":"github.com/alrayyes/golanghelloworld"}
{"Time":"2025-02-14T17:39:12.409705024+01:00","Action":"run","Package":"github.com/alrayyes/golanghelloworld","Test":"TestCmdOutput"}
{"Time":"2025-02-14T17:39:12.409719621+01:00","Action":"output","Package":"github.com/alrayyes/golanghelloworld","Test":"TestCmdOutput","Output":"=== RUN   TestCmdOutput\n"}
{"Time":"2025-02-14T17:39:12.409736633+01:00","Action":"output","Package":"github.com/alrayyes/golanghelloworld","Test":"TestCmdOutput","Output":"--- PASS: TestCmdOutput (0.00s)\n"}
{"Time":"2025-02-14T17:39:12.409741492+01:00","Action":"pass","Package":"github.com/alrayyes/golanghelloworld","Test":"TestCmdOutput","Elapsed":0}
{"Time":"2025-02-14T17:39:12.409747975+01:00","Action":"output","Package":"github.com/alrayyes/golanghelloworld","Output":"PASS\n"}
{"Time":"2025-02-14T17:39:12.410061284+01:00","Action":"output","Package":"github.com/alrayyes/golanghelloworld","Output":"ok  \tgithub.com/alrayyes/golanghelloworld\t0.002s\n"}
{"Time":"2025-02-14T17:39:12.410074068+01:00","Action":"pass","Package":"github.com/alrayyes/golanghelloworld","Elapsed":0.002}

Example code

#

The example code can be found here: