No sum types — only interface{} with type-switch.
No exhaustiveness check from the compiler — only the exhaustive linter.
No Option<T> — only nil and the eternal trap of "is this nil interface or nil concrete?".
No Result<T, E> — only (T, error), no compiler enforcement of unwrapping.
No newtype that prevents primitive coercion — type UserID string is still implicitly convertible from a literal when used carelessly.

This is the whole point of the skill. Where the language is weak, the linter bundle becomes the type checker, and code patterns become the type system. Treat golangci-lint v2 with the configuration in golangci-strict.md as if it were tsc --strict or basedpyright. Treat nilaway and go test -race as if they were Miri.

The skill enforces five non-negotiables:

Parse-don't-validate at every boundary. HTTP/RPC/CLI/config gets parsed into a domain struct constructed only via New*(...) smart constructors. Once inside the domain, no further validation. See data-modeling.md.
(T, error) everywhere. No panics in library code. No bare _ = err. Errors are wrapped with %w and asserted with errors.Is / errors.As. Typed error structs for anything a caller can branch on. See error-handling.md.
Sealed interfaces for variants. Sum types via a sealed unexported method, dispatched through a type switch, with the exhaustive linter checking completeness. See type-patterns.md.
context.Context is the first parameter. Always. No context.Background() inside leaf functions. No goroutine without context-driven shutdown. No time.Now() in domain code — inject a clock. See concurrency.md.
Generated, not hand-written, for external contracts. sqlc for DB, oapi-codegen for OpenAPI servers and clients, protoc-gen-go + protoc-gen-connect-go for RPC. Hand-rolled marshalling is a regression. See sqlc-pgx.md, grpc-connect.md.

Hard rules — tooling

Category	Use	Never
Go version	1.23+ (range-over-func, iter package, slog stable)	<1.22
Module	`go modules` + `go work` for monorepos	dep, GOPATH layouts
Format	`gofumpt` (stricter gofmt) + `goimports -local <module>`	bare `gofmt`
Linter	`golangci-lint v2` with the strict bundle in `golangci-strict.md`	bare `go vet`
Nil checker	`nilaway` (Uber, stable since 2024) in CI	hope
Vet bundle	`go vet` + `fieldalignment` + `shadow`	"tests cover it"
Tests	`go test -race -shuffle=on -count=1`	`-count` cache, no race
Goroutine leaks	`go.uber.org/goleak` in `TestMain`	"looks fine"
Mock	`go.uber.org/mock` (gomock successor)	hand-written stubs
DB	`sqlc` + `jackc/pgx/v5`	`database/sql` + `gorm`
HTTP framework	`gin-gonic/gin` (de facto, ~48% of Go API repos) — `go-chi/chi` for minimalist, `connectrpc/connect-go` for RPC	`echo` (smaller eco), `fiber` (fasthttp = non-stdlib), `gorilla/mux` (in maintenance mode)
RPC	`connectrpc/connect-go` (gRPC-compatible, HTTP/1.1-friendly, browser-friendly)	hand-rolled `grpc-go` unless you specifically need bidi streaming features Connect lacks
Validation	`go-playground/validator/v10` for HTTP boundary + `bufbuild/protovalidate-go` for proto + smart constructors for domain	ad-hoc `if len(s) == 0` chains
Config	`caarlos0/env/v11` (struct-tag env)	`viper` unless you actually need file+env+flag merging
Logging	`log/slog` (stdlib, Go 1.21+)	logrus, zap, zerolog (all superseded)
CLI	`spf13/cobra`	hand-rolled `os.Args` parsing past 2 flags
TUI	`charm.land/bubbletea/v2` + `bubbles/v2` + `lipgloss/v2` — see `bubbletea-v2.md` for CJK/IME	bubbletea v1 if you need IME

A single CI command should be the gate:

gofumpt -l . && \
  golangci-lint run ./... && \
  nilaway ./... && \
  go test -race -shuffle=on -count=1 ./...

If any of these fails, the change is not done. Period. The bundle is set up so a clean run actually means clean — see golangci-strict.md for the per-linter rationale and the deliberate nolint: policy.

Hard rules — code

Read these per-file references for the canonical patterns:

Types & data → type-patterns.md, data-modeling.md — branded named types, smart constructors with unexported fields, sealed interfaces as sum types.
Errors → error-handling.md — sentinel vs typed struct, errors.Is/As, %w wrapping, no panic in libraries, the errorlint ruleset.
Concurrency → concurrency.md — context.Context discipline, errgroup, sync.OnceValue, goleak, -race, channel selection rules.
HTTP backend → backend-stack.md — gin server skeleton, middleware ordering, SSE/streaming with http.Flusher, structured slog logging, graceful shutdown — distilled from the CLIProxyAPI codebase (a real proxy serving OpenAI/Gemini/Claude APIs).
RPC → grpc-connect.md — when to pick Connect vs grpc-go, codegen pipeline, protovalidate, streaming.
DB → sqlc-pgx.md — compile-time-safe SQL via sqlc + pgx connection pool + migrations via goose + testcontainers in CI.
CLI → cobra-stack.md — cobra layout, slog integration, graceful shutdown on signals, fang-style colored help.
TUI → bubbletea-v2.md — v2 model, SetVirtualCursor(false) + tea.View{Cursor} for CJK IME, why v1 was broken for Korean/Japanese/Chinese input.
Testing → testing.md — table-driven tests, require vs assert, autogold snapshots, gopter property tests, testcontainers for integration, goleak for goroutine leaks.
Bootstrap → bootstrap.md — new-project.go invocation, project layout (cmd/, internal/, pkg/), Taskfile, CI.
Strict config → golangci-strict.md — the canonical .golangci.yml with the full linter whitelist and per-linter rationale.
One-liners → one-liners.md — go run scripts with //go:build ignore, gorun-style invocation.

The 250 pure LOC ceiling

Same rule as Python/Rust/TS: a .go file whose pure LOC (non-blank, non-comment) exceeds 250 is architecturally broken. Go encourages many small files in a single package, so this is more natural here than elsewhere — split by responsibility, keep one cohesive type and its methods per file.

The cmd/server/main.go is the most common violator. Refactor it: main.go only wires os.Args → cmd.Execute(). Anything else lives in internal/.

Existing codebases — non-strict project

When editing an existing .go file that doesn't follow these rules: write new code in strict style, don't refactor existing code in the same change. Use the remove-ai-slops skill for branch-scope cleanup.

Activation

This skill activates whenever you write or modify any .go file, go.mod, go.sum, .golangci.yml, Taskfile.yml, or any of the codegen specs (*.proto, *.sql next to sqlc.yaml, openapi.yaml next to oapi-codegen.yaml). Even one-off scripts get the strict treatment — that is what //go:build ignore + go run is for: production hygiene with throwaway ergonomics.

The references contain the recipes. Read them before writing code. Re-read them when the model drifts. The post-write architectural review loop is non-negotiable.