the minimalist URL shortener
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klein is a minimalist URL shortener written in Go. No unnecessary clutter, web UI, features, etc. Just shortening and serving redirections.


klein has three core components that are abstracted into "modules" to allow different functionality:

  1. auth
    • Handles authentication, guarding access to shortening links
    • Comes with two modules:
      • Unauthenticated—shorten URLs without authentication
      • Static Key—require a static key/password
      • HTTP Basic—uses HTTP Basic Auth, require a username and password
  2. alias
    • Handles generating URL aliases.
    • Comes with two modules:
      • Alphanumeric—returns a random alphanumeric string with a configurable length
      • Memorable—returns a configurable amount of English words
  3. storage
    • Handles storing and reading shortened URLs.
    • Comes with four modules:
      • File—stores URL data as text files in a directory
      • Bolt—stores URL data in a bolt database
      • Redis—stores URL data in a redis database (ensure you configure save)
      • Spaces-stores URL data in DigitalOcean Spaces


Once installed and configured, there are two actions that you can do:

  1. Shorten a URL:
    • Send a POST request to / with the following two fields:
      1. url—the URL to shorten
      2. key—if the Static Key auth module is enabled
      3. alias—a custom alias to be used instead of a randomly-generated one
    • Example cURL command: curl -X POST -d 'url=' -d 'key=secret_password' -d 'alias=klein_gh' http://localhost:5556/
      • This will create a short URL at http://localhost:5556/klein_gh that redirects to
  2. Look up a URL/serve a redirect:
    • Browse to http://[path to klein]/[alias] to access a short URL.


Use the docker image kamaln7/klein. The latest tag is a good bet.

Or grab the latest binary from the releases page and drop it in /usr/local/bin, /opt, or wherever you like.


klein uses CLI options for config.

./klein --help
klein is a minimalist URL shortener.

  klein [flags]

      --alias string                       what alias generation to use (alphanumeric, memorable) (default "alphanumeric")
      --alias.alphanumeric.alpha           use letters in code (default true)
      --alias.alphanumeric.length int      alphanumeric code length (default 5)
      --alias.alphanumeric.num             use numbers in code (default true)
      --alias.memorable.length int         memorable word count (default 3)
      --auth string                        what auth backend to use (basic, key, none) (default "none")
      --auth.basic.password string         password for HTTP basic auth
      --auth.basic.username string         username for HTTP basic auth
      --auth.key string                    upload API key
  -h, --help                               help for klein
      --listen string                      listen address (default "")
      --root string                        root redirect
      --storage string                     what storage backend to use (file, boltdb, redis, spaces) (default "file")
      --storage.boltdb.path string         path to use for bolt db (default "bolt.db")
      --storage.file.path string           path to use for file store (default "urls")
      --storage.redis.address string       address:port of redis instance (default "")
      --storage.redis.auth string          password to access redis
      --storage.redis.db int               db to select within redis
      --storage.spaces.access_key string   access key for spaces
      --storage.spaces.path string         path of the file in spaces (default "klein.json")
      --storage.spaces.region string       region for spaces
      --storage.spaces.secret_key string   secret key for spaces string        space to use
      --template string                    path to error template
      --url string                         path to public facing url

You can also use environment variables for configuration. For environment variables, each option is prefixed with klein and dots are replaced with underscores, eg the environment variable for the auth.key option is KLEIN_AUTH_KEY.

Service file

Here's a SystemD service file that you can use with klein:






Don't forget to add your config to the ExecStart line and update User and Group if necessary. Make sure that klein has permission to write to the URLs directory.


To manage dependencies, we use dep. To install dependencies for this project, install dep, and then run dep ensure in this workspace.

To build the app, run go build.
This will produce a binary named klein. You can now run the app by running ./klein

❤️ Contributors

  • @LukeHandle
  • @DMarby