Standard Library

Run ships with a comprehensive standard library, comparable in scope to Go’s. It covers the most common tasks so you can build real applications without third-party dependencies.

Core packages

Package	Description
fmt	String formatting and printing
strings	String searching, splitting, joining
bytes	Byte slice utilities
math	Mathematical functions and constants
time	Time, durations, and timers

I/O and system

Package	Description
io	Readers, writers, buffered I/O
os	File system, processes, environment
log	Structured logging

Networking

Package	Description
net	TCP/UDP sockets, DNS resolution
http	HTTP server and client

Data and encoding

Package	Description
json	JSON encoding and decoding
crypto	Hashing, encryption, TLS

Concurrency and testing

Package	Description
sync	Mutexes, atomics, wait groups
testing	Built-in test framework

Example: a small HTTP server

package main

use "http"
use "fmt"

fun handle(w: &http.ResponseWriter, r: @http.Request) {
    w.write("Hello from Run!")
}

pub fun main() {
    http.handlefn("/", handle)
    fmt.println("listening on :8080")
    http.listenAndServe(":8080")
}

The standard library is designed to be practical and unsurprising. When you need something common — reading a file, serving HTTP, encoding JSON — it is already there.