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The shards command

Crystal is typically accompanied by Shards, its dependency manager.

It manages dependencies for Crystal projects and libraries with reproducible installs across computers and systems.


Shards is usually distributed with Crystal itself. Alternatively, a separate shards package may be available for your system.

To install from source, download or clone the repository and run make CRFLAGS=--release. The compiled binary is in bin/shards and should be added to PATH.


shards requires the presence of a shard.yml file in the project folder (working directory). This file describes the project and lists dependencies that are required to build it. A default file can be created by running shards init. The file's contents are explained in the Writing a Shard guide and a detailed description of the file format is provided by the shard.yml specification.

Running shards install resolves and installs the specified dependencies. The installed versions are written into a shard.lock file for using the exact same dependency versions when running shards install again.

If your shard builds an application, both shard.yml and shard.lock should be checked into version control to provide reproducible dependency installs. If it is only a library for other shards to depend on, shard.lock should not be checked in, only shard.yml. It's good advice to add it to .gitignore (the crystal init does this automatically when initializing a lib repository).

Shards commands

shards [<options>...] [<command>]

If no command is given, install will be run by default.

To see the available options for a particular command, use --help after a command.

Common options:

  • --version: Prints the version of shards.
  • -h, --help: Prints usage synopsis.
  • --no-color: Disabled colored output.
  • --production: Runs in release mode. Development dependencies won't be installed and only locked dependencies will be installed. Commands will fail if dependencies in shard.yml and shard.lock are out of sync (used by install, update, check and list command)
  • -q, --quiet: Decreases the log verbosity, printing only warnings and errors.
  • -v, --verbose: Increases the log verbosity, printing all debug statements.

shards build

shards build [<targets>] [<options>...]

Builds the specified targets in bin path. If no targets are specified, all are built. This command ensures all dependencies are installed, so it is not necessary to run shards install before.

All options following the command are delegated to crystal build.

shards check

shards check

Verifies that all dependencies are installed and requirements are satisfied.

Exit status:

  • 0: Dependencies are satisfied.
  • 1: Dependencies are not satisfied.

shards init

shards init

Initializes a shard folder and creates a shard.yml.

shards install

shards install

Resolves and installs dependencies into the lib folder. If not already present, generates a shard.lock file from resolved dependencies, locking version numbers or Git commits.

Reads and enforces locked versions and commits if a shard.lock file is present. The install command may fail if a locked version doesn't match a requirement, but may succeed if a new dependency was added, as long as it doesn't generate a conflict, thus generating a new shard.lock file.

shards list

shards list

Lists the installed dependencies and their versions.

shards prune

shards prune

Removes unused dependencies from lib folder.

shards update

shards update

Resolves and updates all dependencies into the lib folder again, whatever the locked versions and commits in the shard.lock file. Eventually generates a new shard.lock file.

shards version

shards version [<path>]

Prints the version of the shard.

Fixing Dependency Version Conflicts

A shard.override.yml file allows overriding the source and restriction of dependencies. An alternative location can be configured with the env var SHARDS_OVERRIDE.

The file contains a YAML document with a single dependencies key. It has the same semantics as in shard.yml. Dependency configuration takes precedence over the configuration in shard.yml or any dependency’s shard.yml.

Use cases are local working copies, forcing a specific dependency version despite mismatching constraints, fixing a dependency, checking compatibility with unreleased dependency versions.

Example file contents

  # Assuming we have a conflict with the version of the Redis shard
  # This will override any specified version and use the `master` branch instead
    github: jgaskins/redis
    branch: master