---
name: go-packages
description: Use when creating Go packages, organizing imports, managing dependencies, or deciding how to structure Go code into packages. Also use when starting a new Go project or splitting a growing codebase into packages, even if the user doesn't explicitly ask about package organization. Does not cover naming individual identifiers (see go-naming).
---
# Go Packages and Imports
## Resource Routing
- `references/IMPORTS.md` - Read when grouping imports, using blank imports, dot imports, or import aliases.
- `references/PACKAGE-SIZE.md` - Read when splitting packages, avoiding `init`, structuring `main`, or designing CLI flags/subcommands.
> **When this skill does NOT apply**: For naming individual identifiers within a package, see [go-naming](../go-naming/SKILL.md). For organizing functions within a single file, see [go-functions](../go-functions/SKILL.md). For configuring linters that enforce import rules, see [go-linting](../go-linting/SKILL.md).
## Package Organization
### Avoid Util Packages
Package names should describe what the package provides. Avoid generic names
like `util`, `helper`, `common` — they obscure meaning and cause import
conflicts.
```go
// Good: Meaningful package names
db := spannertest.NewDatabaseFromFile(...)
_, err := f.Seek(0, io.SeekStart)
// Bad: Vague names obscure meaning
db := test.NewDatabaseFromFile(...)
_, err := f.Seek(0, common.SeekStart)
```
Generic names can be used as *part* of a name (e.g., `stringutil`) but should
not be the entire package name.
### Package Size
| Question | Action |
|----------|--------|
| Can you describe its purpose in one sentence? | No → split by responsibility |
| Do files never share unexported symbols? | Those files could be separate packages |
| Distinct user groups use different parts? | Split along user boundaries |
| Godoc page overwhelming? | Split to improve discoverability |
**Do NOT split** just because a file is long, to create single-type packages, or
if it would create circular dependencies.
---
## Imports
Imports are organized in groups separated by blank lines. Standard library
packages always come first. Use
[goimports](https://pkg.go.dev/golang.org/x/tools/cmd/goimports) to manage this
automatically.
```go
import (
"fmt"
"os"
"github.com/foo/bar"
"rsc.io/goversion/version"
)
```
**Quick rules:**
| Rule | Guidance |
|------|----------|
| Grouping | stdlib first, then external. Extended: stdlib → other → protos → side-effects |
| Renaming | Avoid unless collision. Rename the most local import. Proto packages get `pb` suffix |
| Blank imports (`import _`) | Only in `main` packages or tests |
| Dot imports (`import .`) | Never use, except for circular-dependency test files |
---
## Avoid init()
Avoid `init()` where possible. When unavoidable, it must be:
1. Completely deterministic
2. Independent of other `init()` ordering
3. Free of environment state (env vars, working dir, args)
4. Free of I/O (filesystem, network, system calls)
**Acceptable uses**: complex expressions that can't be single assignments,
pluggable hooks (e.g., `database/sql` dialects), deterministic precomputation.
---
## Exit in Main
Call `os.Exit` or `log.Fatal*` **only in `main()`**. All other functions should
return errors.
**Why**: Non-obvious control flow, untestable, `defer` statements skipped.
**Best practice**: Use the `run()` pattern — extract logic into
`func run() error`, call from `main()` with a single exit point:
```go
func main() {
if err := run(); err != nil {
log.Fatal(err)
}
}
```
---
## Command-Line Flags
> **Advisory**: Define flags only in `package main`.
- Flag names use `snake_case`: `--output_dir` not `--outputDir`
- Libraries should accept configuration as parameters, not read flags directly —
this keeps them testable and reusable
- Prefer the standard `flag` package; use `pflag` only when POSIX conventions
(double-dash, single-char shortcuts) are required
```go
// Good: Flag in main, passed as parameter to library
func main() {
outputDir := flag.String("output_dir", ".", "directory for output files")
flag.Parse()
if err := mylib.Generate(*outputDir); err != nil {
log.Fatal(err)
}
}
```
---
## Related Skills
- **Package naming**: See [go-naming](../go-naming/SKILL.md) when choosing package names, avoiding stuttering, or naming exported symbols
- **Error handling across packages**: See [go-error-handling](../go-error-handling/SKILL.md) when wrapping errors at package boundaries with `%w` vs `%v`
- **Import linting**: See [go-linting](../go-linting/SKILL.md) when configuring goimports local-prefixes or enforcing import grouping
- **Global state**: See [go-defensive](../go-defensive/SKILL.md) when replacing `init()` with explicit initialization or avoiding mutable globals