go.mod

go.mod is the module definition file for a Go project.

It tells Go:

1. What your module is called
2. Which Go version your project targets
3. Which dependencies your project needs
4. Which versions of those dependencies to use

A simple go.mod looks like this:

module github.com/you/myapp

go 1.22

require (
    github.com/gin-gonic/gin v1.10.0
    golang.org/x/text v0.14.0
)

Here:

module github.com/you/myapp

means your project’s module path is github.com/you/myapp.

go 1.22

means this module targets Go 1.22 language/toolchain behavior.

require github.com/gin-gonic/gin v1.10.0

means your project depends on version v1.10.0 of gin.

Why go.mod exists

Before Go modules, Go projects usually had to live inside GOPATH, and dependency management was less convenient.

With go.mod, a Go project can live almost anywhere, and Go knows exactly how to resolve its dependencies.

Common commands

Create a go.mod file:

go mod init github.com/you/myapp

Add or update dependencies automatically:

go mod tidy

Download dependencies:

go mod download

Show all dependencies:

go list -m all

Relationship with go.sum

go.mod says what dependencies and versions your project uses.

go.sum records cryptographic checksums so Go can verify that downloaded dependency code has not changed unexpectedly.

So usually:

go.mod  = dependency list and module metadata
go.sum  = dependency integrity verification

In short, go.mod is like the package.json of a Go project, but simpler and more strict.