seikaikyo/golang-dependency-management

Persona: You are a Go dependency steward. You treat every new dependency as a long-term maintenance commitment — you ask whether the standard library already solves the problem before reaching for an external package.

Dependencies:

• govulncheck: go install golang.org/x/vuln/cmd/govulncheck@latest

Go Dependency Management

AI Agent Rule: Ask Before Adding Dependencies

Before running go get to add any new dependency, AI agents MUST ask the user for confirmation. AI agents can suggest packages that are unmaintained, low-quality, or unnecessary when the standard library already provides equivalent functionality. Using go get -u to upgrade an existing dependency is safe.

Before proposing a dependency, evaluate:

• Does the standard library already cover the use case?
• Is the license compatible?
• Are there well-known alternatives?
• What it does and why it's needed?

The samber/cc-skills-golang@golang-popular-libraries skill contains a curated list of vetted, production-ready libraries. Prefer recommending packages from that list. When no vetted option exists, favor well-known packages from the Go team (golang.org/x/...) or established organizations over obscure alternatives.

Key Rules

• go.sum MUST be committed — it records cryptographic checksums of every dependency version, letting go mod verify detect supply-chain tampering. Without it, a compromised proxy could silently substitute malicious code
• govulncheck ./... or go tool govulncheck ./... before every release — catches known CVEs in your dependency tree before they reach production
• Maintenance status, license compatibility, and stdlib alternatives are important considerations before adding a dependency — every dependency increases attack surface, maintenance burden, and binary size
• go mod tidy before every commit that changes dependencies — removes unused modules and adds missing ones, keeping go.mod honest

go.mod & go.sum

Essential Commands

| Command | Purpose | | ----------------- | -------------------------------------------- | | go mod tidy | Add missing deps, remove unused ones | | go mod download | Download modules to local cache | | go mod verify | Verify cached modules match go.sum checksums | | go mod vendor | Copy deps into vendor/ directory | | go mod edit | Edit go.mod programmatically (scripts, CI) | | go mod graph | Print the module requirement graph | | go mod why | Explain why a module or package is needed |

Vendoring

Use go mod vendor when you need hermetic builds (no network access), reproducibility guarantees beyond checksums, or when deploying to environments without module proxy access. CI pipelines and Docker builds sometimes benefit from vendoring. Run go mod vendor after any dependency change and commit the vendor/ directory.

Installing & Upgrading Dependencies

Adding a Dependency

go get github.com/google/uuid          # Latest version
go get github.com/google/[email protected]   # Specific version
go get github.com/google/uuid@latest   # Explicitly latest
go get github.com/google/uuid@<commit> # Specific commit (pseudo-version)

Before pinning a version, inspect the module's available versions, importers, and known vulnerabilities on pkg.go.dev → See samber/cc-skills-golang@golang-pkg-go-dev skill.

Upgrading

go get -u ./...            # Upgrade ALL direct+indirect deps to latest minor/patch
go get -u=patch ./...      # Upgrade to latest patch only (safer)
go get github.com/[email protected] # Upgrade specific package

Prefer go get -u=patch for routine updates. Patch and minor updates are usually lower risk than major upgrades, but still require review. For dependency updates, run:

go get -u=patch ./...
go mod tidy
go test ./...
go vet ./...
govulncheck ./...   # or: go tool govulncheck ./...

Release notes and changelogs for libraries affecting persistence, serialization, networking, authentication, authorization, cryptography, or public APIs may contain important information about breaking changes.

Removing a Dependency

go get github.com/google/uuid@none  # Mark for removal
go mod tidy                          # Clean up go.mod and go.sum

Installing CLI Tools

For Go 1.24+ modules, pin executable tools in go.mod with tool directives. Do not create a new tools.go blank-import file unless the module must support Go <1.24.

# Add tools to the current module.
go get -tool github.com/golangci/golangci-lint/v2/cmd/golangci-lint@latest
go get -tool golang.org/x/vuln/cmd/govulncheck@latest
go get -tool golang.org/x/perf/cmd/benchstat@latest

# Run pinned tools reproducibly.
go tool golangci-lint run ./...
go tool govulncheck ./...
go tool benchstat old.txt new.txt

# Install all module-pinned tools into GOBIN/PATH when needed.
go install tool

# Update pinned tools deliberately, then review go.mod/go.sum.
go get -u tool
go mod tidy

go.mod shape for a module targeting Go 1.26 or newer. This is an example target, not a cap; keep the project's actual go directive and do not change it just to add tools.

module example.com/project

go 1.26

tool (
    github.com/golangci/golangci-lint/v2/cmd/golangci-lint
    golang.org/x/vuln/cmd/govulncheck
    golang.org/x/perf/cmd/benchstat
)

For Go <1.24 only, use the legacy tools.go blank-import workaround:

//go:build tools

package tools

import (
    _ "github.com/golangci/golangci-lint/v2/cmd/golangci-lint"
    _ "golang.org/x/vuln/cmd/govulncheck"
)

Rule: Go 1.24+ = tool directives. Go <1.24 = tools.go fallback.

Go 1.26+ module target note

When using a Go 1.26 or newer toolchain, go mod init may create a module with an older default go directive. If the project intentionally targets Go 1.26+ APIs, update the directive deliberately:

go mod edit -go=1.26
go mod tidy

For future Go versions, use the project's intended target version. Do not use APIs newer than the module's go directive until the project explicitly agrees to upgrade it.

Deep Dives

• Versioning & MVS — Semantic versioning rules (major.minor.patch), when to increment each number, pre-release versions, the Minimal Version Selection (MVS) algorithm (why you can't just pick "latest"), and major version suffix conventions (v0, v1, v2 suffixes for breaking changes).

• Auditing Dependencies — Vulnerability scanning with govulncheck, tracking outdated dependencies, analyzing which dependencies make the binary large (goweight), and distinguishing test-only vs binary dependencies to keep go.mod clean.

• Dependency Conflicts & Resolution — Diagnosing version conflicts (what go get does when you request incompatible versions), resolution strategies (replace directives for local development, exclude for broken versions, retract for published versions that should be skipped), and workflows for conflicts across your dependency tree.

• Go Workspaces — go.work files for multi-module development (e.g., library + example application), when to use workspaces vs monorepos, and workspace best practices.

• Automated Dependency Updates — Setting up Dependabot or Renovate for automatic dependency update PRs, auto-merge strategies (when to merge automatically vs require review), and handling security updates.

• Visualizing the Dependency Graph — go mod graph to inspect the full dependency tree, modgraphviz to visualize it, and interactive tools to find which dependency chains cause bloat.

Cross-References

• → See samber/cc-skills-golang@golang-continuous-integration skill for Dependabot/Renovate CI setup
• → See samber/cc-skills-golang@golang-security skill for vulnerability scanning with govulncheck
• → See samber/cc-skills-golang@golang-popular-libraries skill for vetted library recommendations

Quick Reference

# Start a new module
go mod init github.com/user/project

# Add a dependency
go get github.com/google/[email protected]

# Upgrade all deps (patch only, safer)
go get -u=patch ./...

# Remove unused deps
go mod tidy

# Check for vulnerabilities
govulncheck ./...   # or: go tool govulncheck ./...

# Check for outdated deps
go list -u -m -json all | go-mod-outdated -update -direct

# Analyze binary size by dependency
goweight

# Understand why a dep exists
go mod why -m github.com/some/module

# Visualize dependency graph
go mod graph | modgraphviz | dot -Tpng -o deps.png

# Verify checksums
go mod verify