Standard Library

One of Go’s defining characteristics is that the language ships with a comprehensive standard library — no npm install, no pip install, no Maven coordinates required for the vast majority of everyday tasks. The library covers HTTP servers and clients, JSON encoding, cryptography, file I/O, text processing, concurrency primitives, and much more. This philosophy keeps dependency trees shallow, binaries self-contained, and upgrade risks low.

Topic	Package(s)	Lesson
Formatted I/O, text, numbers	`fmt`, `strings`, `strconv`	fmt & strings
Dates, durations, timers	`time`	time
JSON marshaling / unmarshaling	`encoding/json`	encoding/json
Streaming I/O, scanning	`io`, `bufio`	io & bufio

Real Go programs reach for fmt.Println, strings.Split, time.Now, and json.Marshal within the first few lines. Understanding these packages deeply means you will recognise idiomatic Go in any codebase you encounter, and you will reach for the right tool instead of pulling in an extra dependency.

The snippet below touches all four areas in a single main function. Read the output, then trace each call back to its package.

Open in Playground

package main

import (
  "encoding/json"
  "fmt"
  "strings"
  "time"
)

func main() {
  // fmt — formatted output
  fmt.Println("Hello, Go!")
  fmt.Printf("Pi is approximately %.4f\n", 3.14159)
  msg := fmt.Sprintf("2 + 2 = %d", 4)
  fmt.Println(msg)

  // strings — text manipulation
  s := "the quick brown fox"
  fmt.Println(strings.ToUpper(s))
  fmt.Println(strings.Contains(s, "fox"))
  fmt.Println(strings.Join(strings.Split(s, " "), "-"))

  // time — fixed date for deterministic output
  t := time.Date(2024, 1, 2, 15, 4, 5, 0, time.UTC)
  fmt.Println(t.Format("2006-01-02"))

  // encoding/json — marshal a struct
  type Point struct {
    X int `json:"x"`
    Y int `json:"y"`
  }
  p := Point{X: 3, Y: 7}
  b, _ := json.Marshal(p)
  fmt.Println(string(b))
}

Standard Library

Go’s batteries-included standard library

Why standard library first?

A runnable tour