Viper : Go configuration management with Fangs

Viper is a complete configuration solution. Designed to work within an application to handle file based configuration and seamlessly marry that with command line flags which can also be used to control application behavior.

Why Viper?

When building a modern application you don’t want to have to worry about configuration file formats, you want to focus on building awesome software. Viper is here to help with that.

Viper does the following for you:

  1. Find, load and marshall a configuration file in YAML, TOML or JSON.
  2. Provide a mechanism to setDefault values for your different configuration options
  3. Provide a mechanism to setOverride values for options specified through command line flags.
  4. Provide an alias system to easily rename parameters without breaking existing code.
  5. Make it easy to tell the difference between when a user has provided a command line or config file which is the same as the default.

Viper believes that:

  1. command line flags take precedence over options set in config files
  2. config files take precedence over defaults

Config files often can be found in multiple locations. Viper allows you to set multiple paths to search for the config file in.

Viper configuration keys are case insensitive.



import (

viper.SetConfigName("config") // name of config file (without extension)
viper.AddConfigPath("/etc/appname/")   // path to look for the config file in
viper.AddConfigPath("$HOME/.appname")  // call multiple times to add many search paths
viper.ReadInConfig() // Find and read the config file

Setting Defaults

viper.SetDefault("ContentDir", "content")
viper.SetDefault("LayoutDir", "layouts")
viper.SetDefault("Indexes", map[string]string{"tag": "tags", "category": "categories"})

Setting Overrides

viper.Set("Verbose", true)
viper.Set("LogFile", LogFile)

Registering and Using Aliases

viper.RegisterAlias("loud", "Verbose")

viper.Set("verbose", true) // same result as next line
viper.Set("loud", true)   // same result as prior line

viper.GetBool("loud") // true
viper.GetBool("verbose") // true

Getting Values

viper.GetString("logfile") // case insensitive Setting & Getting
if viper.GetBool("verbose") {
    fmt.Println("verbose enabled")

Q & A

Q: Why not INI files?

A: Ini files are pretty awful. There’s no standard format and they are hard to validate. Viper is designed to work with YAML, TOML or JSON files. If someone really wants to add this feature, I’d be happy to merge it. It’s easy to specify which formats your application will permit.

Q: Why is it called “viper”?

A: Viper is designed to be a companion to Cobra. While both can operate completely independently, together they make a powerful pair to handle much of your application foundation needs.

Q: Why is it called “Cobra”?

A: Is there a better name for a commander?

Q: Can I see more examples?

A: Sure, checkout hugo which makes extensive use of both cobra and viper. They were both designed to solve problems I had while building hugo which no existing library could.

Fork me on GitHub