.go File Extension

What kind of file is a .go?

A .go file contains source code for the Go programming language. It is editable text, not a compiled program. Go programs are organized into packages, and all source files for a package are normally kept in the same directory and compiled together.¹ A source file begins with a package clause, followed by optional imports and declarations such as functions, types, variables, and constants.²

The Go specification requires source code to be Unicode text encoded in UTF-8.² There are no fixed magic bytes, so software usually identifies a .go file from its suffix and source syntax. Go has no registered language-specific media type in the IANA registry; text/x-go is used by some software but is unregistered. Poly treats .go as readable text/plain.³

How do I open a .go on my computer?

Any text editor can open .go files on Windows, macOS, or Linux. Visual Studio Code with the Go extension and JetBrains GoLand add formatting, completion, navigation, tests, and debugging. Vim, Neovim, Emacs, and other editors can use Go-aware plugins.

Install the Go toolchain when you need to format, test, or compile a project. From the directory containing its go.mod file, common commands include:

gofmt -w .
go test ./...
go build ./...

go build compiles packages and their dependencies, while go install also installs the resulting executable.⁴ Opening source as text is safe. Building or running an unfamiliar project can execute generators, tests, or application code and may download dependencies, so review it first.

Poly support for .go

Poly opens .go files in a code-friendly viewer with Go syntax highlighting, word wrap, and in-file search. It indexes readable source for exact and semantic search, so you can find a symbol by name or look for code by what it does. The Poly agent can summarize a file, explain a function, and help trace likely behavior.

Poly does not compile or execute code, download modules, run tests, or reproduce a language server's project state. Keep related .go files, go.mod, go.sum, tests, and documentation together when package-level context matters.

History of .go

Robert Griesemer, Rob Pike, and Ken Thompson began designing Go at Google on September 21, 2007. It became a public open-source project on November 10, 2009.⁵ The .go suffix has been the standard convention for Go source throughout its public life.

The language is named Go, not “Golang.” The longer label came from the original golang.org website and remains useful in searches, but it is not the language's official name.⁵

Working with .go and related files

Filename patterns and neighboring files tell the Go toolchain how source participates in a build:

Go's own guide notes that a module contains related packages, while each package is built from the source files in one directory.¹ Keep .go, go.mod, and go.sum files in version control. Use gofmt for consistent formatting, and use the Go toolchain to build or test rather than changing filename extensions.