Golang Spf13 Viper

What it does

When your agent uses it

• Development work in your project

Example prompts

• “/golang-spf13-viper”

Requirements

• Compatibility (from SKILL.md): Designed for Claude Code, Codex or similar harness, and for projects using Golang.
• Pre-approved tools (allowed-tools): Read, Edit, Write, Glob, Grep, Bash(go:*), Bash(golangci-lint:*), Bash(git:*), Agent, WebFetch, mcp__context7__resolve-library-id, mcp__context7__query-docs, Bash(godig:*), Bash(gopls:*), LSP, mcp__gopls__*

Workflow steps

5 steps, taken from the first numbered list in SKILL.md.

1. 1Set prefix + key replacer + AutomaticEnv together — missing any one causes nested env keys to silently not resolve (database.host →…
2. 2Handle ConfigFileNotFoundError gracefully — a missing config file should not crash a service that runs with only flags and env vars.
3. 3Always use mapstructure tags on config structs — implicit mapping silently misses nested and underscore-named fields.
4. 4Use viper.New() in tests, never the global — the global accumulates state across test runs; per-test instances are isolated.
5. 5Bind flags before Execute() — binding in RunE is too late; cobra parses flags before RunE runs.

What it can do on your machine

Read from SKILL.md and the folder at commit 8876467. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves these tools, so the agent can use them without asking each time:

  • Read
  • Edit
  • Write
  • Glob
  • Grep
  • Bash(go:*)
  • Bash(golangci-lint:*)
  • Bash(git:*)
  • Agent
  • WebFetch

  …and 6 more on the same allowed-tools line.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • go

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Links to these hosts (documentation or services it may open):

  • github.com
  • pkg.go.dev

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

• Compatibility

  Designed for Claude Code, Codex or similar harness, and for projects using Golang.

  From compatibility in the SKILL.md frontmatter.

Context cost

Golang Spf13 Viper loads about 2.5k tokens when it runs, and up to ~7k if it reads all its reference files. Until then it costs about 79 tokens; SKILL.md has 844 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~79

When it runs · the whole SKILL.md, loaded when a task matches

~2.5k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~7k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from context-labs/whip at commit 8876467, republished under its MIT licence (© context-labs). 844 words, ~2,454 tokens.

name

golang-spf13-viper

description

Golang configuration library using spf13/viper — layered precedence (flag > env > file > KV > default), AutomaticEnv, ReadInConfig, Unmarshal + mapstructure, WatchConfig hot reload. Apply when using/adopting viper or the codebase imports github.com/spf13/viper. CLI commands: golang-spf13-cobra.

allowed-tools

Read, Edit, Write, Glob, Grep, Bash(go:*), Bash(golangci-lint:*), Bash(git:*), Agent, WebFetch, mcp__context7__resolve-library-id, mcp__context7__query-docs, Bash(godig:*), Bash(gopls:*), LSP, mcp__gopls__*

compatibility

Designed for Claude Code, Codex or similar harness, and for projects using Golang.

user-invocable

true

license

MIT

metadata.author

samber

metadata.version

1.1.0

paths

**/*.go

go get github.com/spf13/viper@latest

1. explicit Set()      — viper.Set("key", val)    highest priority
2. flag                — bound pflag.Flag
3. env var             — BindEnv / AutomaticEnv
4. config file         — ReadInConfig / MergeInConfig
5. KV remote           — etcd / Consul
6. default             — viper.SetDefault("key", val)   lowest priority

viper.SetConfigName("config")
viper.AddConfigPath("$HOME/.myapp")
if err := viper.ReadInConfig(); err != nil {
    var notFound *viper.ConfigFileNotFoundError
    if !errors.As(err, &notFound) {
        return fmt.Errorf("reading config: %w", err) // propagate real errors only
    }
}

// ✓ Good — all three wired together at startup
viper.SetEnvPrefix("MYAPP")                             // prevent collisions: PORT → MYAPP_PORT
viper.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))  // database.host → MYAPP_DATABASE_HOST
viper.AutomaticEnv()

// ✗ Bad — without SetEnvKeyReplacer, viper looks for MYAPP_DATABASE.HOST (dot preserved)

func init() {
    rootCmd.PersistentFlags().Int("port", 8080, "listen port")
    viper.BindPFlag("port", rootCmd.PersistentFlags().Lookup("port"))
    // viper.BindPFlags(cmd.Flags()) — bind an entire FlagSet at once
}

type Config struct {
    Port     int `mapstructure:"port"`
    Database struct {
        MaxConn int `mapstructure:"max_conn"` // explicit tag: mapstructure won't convert underscore→camelCase
    } `mapstructure:"database"`
}
var cfg Config
viper.Unmarshal(&cfg)

viper.WatchConfig()
viper.OnConfigChange(func(e fsnotify.Event) { /* re-apply changed values */ })

v := viper.New()
v.SetConfigFile("testdata/config.yaml")
require.NoError(t, v.ReadInConfig())

© context-labs, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 6 other files (references) in .agents/skills/golang-spf13-viper of context-labs/whip.

• SKILL.md
• evals/evals.json
• references/binding-and-env.md
• references/sources-and-formats.md
• references/testing-and-isolation.md
• references/unmarshal.md
• references/watch-and-reload.md

Open the folder on GitHubat commit 8876467