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Configuration and customisation

Stack is configured by the content of YAML files. Some Stack operations can also be customised by the use of scripts.

YAML configuration

Stack's YAML configuration options break down into project-specific options and non-project-specific options. They are configured at the project-level or globally.

The project-level configuration file (stack.yaml) contains project-specific options and may contain non-project-specific options.

Stack obtains project-level configuration from one of the following (in order of preference):

  1. A file specified by the --stack-yaml command line option.
  2. A file specified by the STACK_YAML environment variable.
  3. A file named stack.yaml in the current directory or an ancestor directory.
  4. A file name stack.yaml in the global-project directory in the Stack root.

The global configuration file (config.yaml) contains only non-project-specific options.

Stack obtains global configuration from a file named config.yaml. The location of this file depends on the operating system and whether Stack is configured to use the XDG Base Directory Specification.

config.yaml is located in /etc/stack (for system-wide options); and/or in the Stack root (for user-specific options).

config.yaml is located in the Stack root.

On Unix-like operating systems and Windows, Stack can be configured to follow the XDG Base Directory Specification if the environment variable STACK_XDG is set to any non-empty value. However, Stack will ignore that configuration if the Stack root location has been set on the command line or the STACK_ROOT environment variable exists.

If Stack is following the XDG Base Directory Specification, the location of config.yaml (for user-specific options) is <XDG_CONFIG_HOME>/stack. If the XDG_CONFIG_HOME environment variable does not exist, the default is ~/.config/stack on Unix-like operating systems and %APPDIR%\stack on Windows.

This page is intended to document fully all YAML configuration options. If you identify any inaccuracies or incompleteness, please update the page, and if you're not sure how, open an issue labeled "question".

If you wish to understand the difference between a stack.yaml files and a Cabal file (named <package_name>.cabal), see the stack.yaml vs a Cabal file documentation.

Project-specific configuration

Project-specific configuration options are valid only in a project-level configuration file (stack.yaml).

Note: We define project to mean a directory that contains a stack.yaml file, which specifies how to build a set of packages. We define package to be a package with a Cabal file or an Hpack package.yaml file.

In your project-specific options, you specify both which local packages to build and which dependencies to use when building these packages. Unlike the user's local packages, these dependencies aren't built by default. They only get built when needed.

Shadowing semantics, described here, are applied to your configuration. So, if you add a package to your packages list, it will be used even if you're using a snapshot that specifies a particular version. Similarly, extra-deps will shadow the version specified in the resolver.

resolver or snapshot

Command line equivalent (takes precedence): --resolver option

resolver and snapshot are synonyms. Only one of these keys is permitted, not both.

The resolver or snapshot key specifies which snapshot is to be used for this project. A snapshot defines a GHC version, a number of packages available for installation, and various settings like build flags. It is called a resolver since a snapshot states how dependencies are resolved. There are currently four resolver types:

  • LTS Haskell snapshots, e.g. resolver: lts-19.17
  • Stackage Nightly snapshots, e.g. resolver: nightly-2002-08-04
  • No snapshot, just use packages shipped with the compiler. For GHC this looks like resolver: ghc-9.2.4
  • Custom snapshot, via a URL or relative file path. For further information, see the Pantry documentation.

Each of these resolvers will also determine what constraints are placed on the compiler version. See the compiler-check option for some additional control over compiler version.

The resolver key corresponds to a Pantry snapshot location. For further information, see the Pantry documentation.



- .

NOTE From Stack 1.11, Stack moved over to Pantry for managing extra-deps, and removed some legacy syntax for specifying dependencies in packages. Some conversion notes are provided below.

The packages key specifies a list of packages that are part of your local project. These are specified via paths to local directories. The paths are considered relative to the directory containing the stack.yaml file. For example, if your stack.yaml is located at /foo/bar/stack.yaml, and you have:

- hello
- there/world

Your configuration means "I have packages in /foo/bar/hello and /foo/bar/there/world.

If these packages should be treated as dependencies instead, specify them in extra-deps key, described below.

The packages key is optional. The default item, '.', means that your project has exactly one package, and it is located in the current directory.

Each package directory specified must have a valid Cabal file or Hpack package.yaml file present. The subdirectories of the directory are not searched for Cabal files. Subdirectories will have to be specified as independent items in the list of packages.

Project packages are different from snapshot dependencies (via resolver) and extra dependencies (via extra-deps) in multiple ways, e.g.:

  • Project packages will be built by default with a stack build without specific targets. Dependencies will only be built if they are depended upon.
  • Test suites and benchmarks may be run for project packages. They are never run for extra dependencies.

Legacy syntax Prior to Stack 1.11, it was possible to specify dependencies in your packages configuration value as well. This support was removed to simplify the file format. Instead, these values should be moved to extra-deps. As a concrete example, you would convert:

- .
- location:
    commit: 08c9b4cdf977d5bcd1baba046a007940c1940758
  extra-dep: true
- location:
    commit: 6bf765e000c6fd14e09ebdea6c4c5b1510ff5376
      - wai-extra
  extra-dep: true

  - streaming-commons-
  - time-1.9.1
  - yesod-colonnade-
  - yesod-elements-1.1


- .

  - streaming-commons-
  - time-1.9.1
  - yesod-colonnade-
  - yesod-elements-1.1
  - git:
    commit: 08c9b4cdf977d5bcd1baba046a007940c1940758
  - git:
    commit: 6bf765e000c6fd14e09ebdea6c4c5b1510ff5376
      - wai-extra

And, in fact, the packages value could be left off entirely since it's using the default value.


Default: []

This key allows you to specify extra dependencies on top of what is defined in your snapshot (specified by the resolver key mentioned above). These dependencies may either come from a local file path or a Pantry package location.

For the local file path case, the same relative path rules as apply to packages apply.

Pantry package locations allow you to include dependencies from three different kinds of sources:

  • Hackage
  • Archives (tarballs or zip files, either local or over HTTP or HTTPS)
  • Git or Mercurial repositories

Here's an example using all of the above:

- vendor/hashable
- streaming-commons-
- time-1.9.1
- yesod-colonnade-
- yesod-elements-1.1
- git:
  commit: 08c9b4cdf977d5bcd1baba046a007940c1940758
- url:
    - wai-extra
- github: snoyberg/conduit
  commit: 2e3e41de93821bcfe8ec6210aeca21be3f2087bf
    - network-conduit-tls

For further information on the format for specifying dependencies, see the Pantry documentation.


Default: {}

Command line equivalent (takes precedence): stack build --flag option

Flags can be set for each package separately. For example:

    flag-name: true

If a specified flag is different than the one specified for a snapshot package, then the snapshot package will automatically be promoted to be an extra-dep.



Default: []

Packages which, when present in the snapshot specified in resolver, should not be included in our package. This can be used for a few different purposes, e.g.:

  • Ensure that packages you don't want used in your project cannot be used in a package.yaml file (e.g., for license reasons)
  • Prevent overriding of a global package like Cabal. For more information, see Stackage issue #4425
  • When using a custom GHC build, avoid incompatible packages (see this comment).
- Cabal
- buggy-package
- package-with-unacceptable-license


If present, specifies a message to be displayed every time the configuration is loaded by Stack. It can serve as a reminder for the user to review the configuration and make any changes if needed. The user can delete this message if the generated configuration is acceptable.

For example, a user-message is inserted by stack init when it omits packages or adds external dependencies, namely:

user-message: ! 'Warning: Some packages were found to be incompatible with the resolver
  and have been left commented out in the packages section.

  Warning: Specified resolver could not satisfy all dependencies. Some external packages
  have been added as dependencies.

  You can omit this message by removing it from stack.yaml



Default: []

Command line equivalent: --customer-preprocessor-extensions option

In order for Stack to be aware of any custom preprocessors you are using, add their extensions here

- erb

TODO: Add a simple example of how to use custom preprocessors.

Non-project-specific configuration

Non-project configuration options are valid in a project-level configuration file (stack.yaml) or in global configuration files (config.yaml). The options below are listed in alphabetic order.


Restrictions: POSIX systems only.

Default: false

Command line equivalent (takes precedence): --[no-]allow-different-user flag

Allow users other than the owner of the Stack root to use the Stack installation.

allow-different-user: true

The intention of this option is to prevent file permission problems, for example as the result of a Stack command executed under sudo.

The option is automatically enabled when Stack is re-spawned in a Docker process.


Default: false

Whether to ignore version bounds in Cabal files. This also ignores lower bounds. The name allow-newer is chosen to match the commonly-used Cabal option.

allow-newer: true




Default: none

Determines a subset of packages to which allow-newer should apply. This option has no effect (but warns) if allow-newer is false.

  - foo
  - bar


Default: locals

Related command line: stack build --ghc-options option

Determines to which packages any GHC command line options specified on the command line are applied. Possible values are: everything (all packages, local or otherwise), locals (all local packages, targets or otherwise), and targets (all local packages that are targets).


The use of everything can break invariants about your snapshot database.


Before Stack, the default value was targets.


Default: The machine architecture on which Stack is running.

Command line equivalent (takes precedence): --arch option

Stack identifies different GHC executables by platform (operating system and machine architecture), (optional) GHC variant and (optional) GHC build. See setup-info.

arch sets the machine architecture. Values are those recognized by Cabal, including x86_64, i386 and aarch64.




  library-profiling: false
  executable-profiling: false
  copy-bins: false
  prefetch: false
  keep-going: false
  keep-tmp-files: false

  # NOTE: global usage of haddock can cause build failures when documentation is
  # incorrectly formatted.  This could also affect scripts which use Stack.
  haddock: false
    haddock-args: []      # Additional arguments passed to haddock, --haddock-arguments
    # haddock-args:
    # - "--css=/home/user/my-css"
  open-haddocks: false    # --open
  haddock-deps: false     # if unspecified, defaults to true if haddock is set
  haddock-internal: false

  # These are inadvisable to use in your global configuration, as they make the
  # Stack build command line behave quite differently.
  test: false
    rerun-tests: true   # Rerun successful tests
    additional-args: [] # --test-arguments
    # additional-args:
    # - "--fail-fast"
    coverage: false
    no-run-tests: false
  bench: false
    benchmark-arguments: ""
    # benchmark-arguments: "--csv bench.csv"
    no-run-benchmarks: false
  force-dirty: false
  reconfigure: false
  cabal-verbose: false
  split-objs: false

  # Since 1.8. Starting with 2.0, the default is true
  interleaved-output: true

  # Since 1.10
  ddump-dir: ""

Command line equivalents (take precedence): Yes, see below.

Allows setting build options which are usually specified on the command line.

The meanings of these settings correspond directly with the command line flags of the same name. For further information, see the stack build command documentation and the users guide.


Command line equivalent (takes precedence): --color option

This option specifies when to use color in output. The option is used as color: <WHEN>, where <WHEN> is 'always', 'never', or 'auto'. On Windows versions before Windows 10, for terminals that do not support color codes, the default is 'never'; color may work on terminals that support color codes.

(The British English spelling (colour) is also accepted. In yaml configuration files, the American spelling is the alternative that has priority.)


Command line equivalent (takes precedence): --compiler option

Overrides the compiler version in the resolver. Note that the compiler-check flag also applies to the version numbers. This uses the same syntax as compiler resolvers like ghc-9.2.4. This can be used to override the compiler for a Stackage snapshot, like this:

resolver: lts-14.20
compiler: ghc-8.6.4
compiler-check: match-exact

Building GHC from source



Stack supports building the GHC compiler from source. The version to build and to use is defined by a a Git commit ID and an Hadrian "flavour" (Hadrian is the build system of GHC) with the following syntax:

compiler: ghc-git-COMMIT-FLAVOUR

In the following example the commit ID is "5be7ad..." and the flavour is "quick":

compiler: ghc-git-5be7ad7861c8d39f60b7101fd8d8e816ff50353a-quick

By default the code is retrieved from the main GHC repository. If you want to select another repository, set the "compiler-repository" option:

compiler-repository: git://my/ghc/repository
# default
# compiler-repository:

Note that Stack doesn't check the compiler version when it uses a compiler built from source. Moreover it is assumed that the built compiler is recent enough as Stack doesn't enable any known workaround to make older compilers work.

Building the compiler can take a very long time (more than one hour). Hint: for faster build times, use Hadrian flavours that disable documentation generation.

Global packages

The GHC compiler you build from sources may depend on unreleased versions of some global packages (e.g. Cabal). It may be an issue if a package you try to build with this compiler depends on such global packages because Stack may not be able to find versions of those packages (on Hackage, etc.) that are compatible with the compiler.

The easiest way to deal with this issue is to drop the offending packages as follows. Instead of using the packages specified in the resolver, the global packages bundled with GHC will be used.

- Cabal
- ...

Another way to deal with this issue is to add the relevant packages as extra-deps built from source. To avoid mismatching versions, you can use exactly the same commit id you used to build GHC as follows:

- git:
  commit: 5be7ad7861c8d39f60b7101fd8d8e816ff50353a
    - libraries/Cabal/Cabal
    - libraries/...

Bootstrapping compiler

Building GHC from source requires a working GHC (known as the bootstrap compiler). As we use a Stack based version of Hadrian (hadrian/build-stack in GHC sources), the bootstrap compiler is configured into hadrian/stack.yaml and fully managed by Stack.


Default: match-minor

Specifies how the compiler version in the resolver is matched against concrete versions. Valid values:

  • match-minor: make sure that the first three components match, but allow patch-level differences. For example< and would both match 7.8.4. This is useful to allow for custom patch levels of a compiler.
  • match-exact: the entire version number must match precisely
  • newer-minor: the third component can be increased, e.g. if your resolver is ghc-7.10.1, then 7.10.2 will also be allowed. This was the default up through Stack 0.1.3


Default: true

This option specifies whether test suites should be executed concurrently with each other. The default is true since this is usually fine and it often means that tests can complete earlier. However, if some test suites require exclusive access to some resource, or require a great deal of CPU or memory resources, then it makes sense to set this to false.

concurrent-tests: false



Options which are passed to the configure step of the Cabal build process. These can either be set by package name, or using the $everything, $targets, and $locals special keys. These special keys have the same meaning as in ghc-options.

  - --with-gcc
  - /some/path
  - --another-flag


Default: 8

Integer indicating how many simultaneous downloads are allowed to happen.


Default: new-template in the stack-templates repository.

This option specifies which template to use with stack new, when none is specified. Other templates are listed in the stack-templates repository. See the output of stack templates.


Command line equivalents: --docker-* flags and options (see stack --docker-help for details).

For further information, see the Docker integration documentation.



Default: warning

Command line equivalent (takes precedence): --[no-]dump-logs flag

In the case of non-interleaved output and more than one target package, Stack sends the build output from GHC for each target package to a log file, unless an error occurs. For further information, see the stack build --[no-]interleaved-output flag documentation.

The value of the dump-logs key controls what, if any, log file content is sent ('dumped') to the console at the end of the build. Possible values are:

dump-logs: none      # don't dump the content of any log files
dump-logs: warning   # dump the content of log files that are warnings
dump-logs: all       # dump all of the content of log files

At the command line, --no-dump-logs is equivalent to dump-logs: none and --dump-logs is equivalent to dump-logs: all.


Default: []

Command line equivalent: --extra-include-dirs option (repeat for each directory)

A list of extra paths to be searched for header files. Paths should be absolute

- /opt/foo/include

Since these are system-dependent absolute paths, it is recommended that you specify these in your config.yaml file. If you control the build environment in your project's stack.yaml, perhaps through docker or other means, then it may well make sense to include these there as well.


Default: []

Command line equivalent: --extra-lib-dirs option (repeat for each directory)

A list of extra paths to be searched for libraries. Paths should be absolute

- /opt/foo/lib

Since these are system-dependent absolute paths, it is recommended that you specify these in your config.yaml file. If you control the build environment in your project's stack.yaml, perhaps through Docker or other means, then it may well make sense to include these there as well.


This option specifies additional directories to prepend to the PATH. These will be used when resolving the location of executables, and will also be visible in the PATH of processes run by Stack.

For example, to prepend /path-to-some-dep/bin to your PATH:

- /path-to-some-dep/bin

Other paths added by Stack - things like the project's binary directory and the compiler's binary directory - will take precedence over those specified here (the automatic paths get prepended).



Default: standard

Command line equivalent (takes precedence): --ghc-build option

Stack identifies different GHC executables by platform (operating system and machine architecture), (optional) GHC variant and (optional) GHC build. See setup-info.

ghc-build specifies a specialized architecture for the GHC executable. Normally this is determined automatically, but it can be overridden. Possible arguments include standard, gmp4, nopie, tinfo6, tinfo6-libc6-pre232, tinfo6-nopie, ncurses6, int-native and integersimple.


Default: {}

Related command line (takes precedence): stack build --ghc-options option

ghc-options can specify GHC command line options for a named package, all local packages that are targets (using the $targets key), all local packages (targets or otherwise) (using the $locals key), or all packages (local or otherwise) (using the $everything key).

  "$everything": -O2
  "$locals": -Wall
  "$targets": -Werror
  some-package: -DSOME_CPP_FLAG

GHC's command line options are order-dependent and evaluated from left to right. Later options can override earlier options. Stack applies options (as applicable) in the order of $everything, $locals, $targets, and then those for the named package. Any existing GHC command line options of a package are applied after those specified in Stack's YAML configuration.

Since Stack 1.6.1, setting a GHC options for a specific package will automatically promote it to a local package (much like setting a custom package flag). However, setting options via $everything on all flags will not do so (see GitHub discussion for reasoning). This can lead to unpredictable behavior by affecting your snapshot packages.


Before Stack 1.6.1, the key * (then deprecated) had the same function as the key $everything.


Default: standard

Command line equivalent (takes precedence): --ghc-variant option

Stack identifies different GHC executables by platform (operating system and machine architecture), (optional) GHC variant and (optional) GHC build. See setup-info.

ghc-variant specifies a variant of the GHC executable. Known values are:

  • standard: Use the standard GHC binary distribution
  • int-native: From GHC 9.4.1, use a GHC bindist that uses the Haskell-native big-integer backend. For further information, see this article.
  • integersimple: Use a GHC bindist that uses integer-simple instead of GMP
  • any other value: Use a custom GHC bindist. You should specify setup-info or setup-info-locations so stack setup knows where to download it, or pass the stack setup --ghc-bindist argument on the command-line

This option is incompatible with system-ghc: true.




Sets the address of the Hackage server to upload the package to.



Default: true ( 2.1.1)

Whether to use the -fhide-source-paths option by default for GHC >= 8.2:

hide-source-paths: false

Build output when enabled:

[1 of 2] Compiling Lib
[2 of 2] Compiling Paths_test_pr

Build output when disabled:

[1 of 2] Compiling Lib              ( src/Lib.hs, .stack-work/dist/x86_64-linux-tinfo6/Cabal- )


Default: true

Strip out the "Loading ..." lines from GHC build output, produced when using Template Haskell.


(Removed 1.11)

This flag was introduced in Stack 1.6, and removed on the move to Pantry. You will receive a warning if this configuration value is set.


Default: true ( 1.5.0)

Command line equivalent (takes precedence): --[no-]install-ghc flag

Whether or not to automatically install GHC when necessary.


Default: the number of processors reported by your CPU.

Command line equivalent (takes precedence): -j, --jobs option

Specifies how many build tasks should be run in parallel. One usage for this might be to avoid running out of memory by setting it to 1, like this:

jobs: 1


Default (on Unix-like operating systems): ~/.local/bin

Default (on Windows): %APPDATA%\local\bin

Command line equivalent (takes precedence): --local-bin-path option

Target directory for stack install and stack build --copy-bins.



The behaviour of this option differs between Unix-like operating systems and Windows.

Default: programs directory in the Stack root.

This overrides the location of the Stack 'programs' directory, where tools like GHC get installed.

Default: %LOCALAPPDATA%\Programs\stack, if the %LOCALAPPDATA% environment variable exists.

This overrides the location of the Stack 'programs' directory, where tools like GHC and MSYS2 get installed.


If there is a space character in the %LOCALAPPDATA% path (which may be the case if the relevant user account name and its corresponding user profile path have a space) this may cause problems with building packages that make use of the GNU project's autoconf package and configure shell script files. That may be the case particularly if there is no corresponding short name ('8 dot 3' name) for the directory in the path with the space (which may be the case if '8 dot 3' names have been stripped or their creation not enabled by default). If there are problems building, it will be necessary to override the default location of Stack's 'programs' directory to specify an alternative path that does not contain space characters. Examples of packages on Hackage that make use of configure are network and process.


Restrictions: Windows systems only.

Default: true

Command line equivalent (takes precedence): --[no-]modify-code-page flag

Whether to modify the code page for UTF-8 output.

modify-code-page: false



  add-gc-roots: false
  enable: false
  nix-shell-options: []
  packages: []
  path: []
  pure: true

Command line equivalents: --nix-* flags and options (see stack --nix-help for details).

For further information, see the Nix integration documentation.




    - 0a5c7ea47cd1b15f01f5f51a33adda7e655bc0f0b0615baa8e271f4c3351e21d
    - 1ea9ba32c526d1cc91ab5e5bd364ec5e9e8cb67179a471872f6e26f0ae773d42
    - 2c6c3627bd6c982990239487f1abd02e08a02e6cf16edb105a8012d444d870c3
    - 51f0161b906011b52c6613376b1ae937670da69322113a246a09f807c62f6921
    - fe331502606802feac15e514d9b9ea83fee8b6ffef71335479a2e68d84adc6b0
    key-threshold: 3
    ignore-expiry: true

Takes precedence over the package-indices key, which is deprecated.

Specify the package index. The index must use the Hackage Security format. This setting is most useful for providing a mirror of the official Hackage server for

  • bypassing a firewall; or
  • faster downloads.

If the setting specifies an index that does not mirror Hackage, it is likely that will result in significant breakage, including most snapshots failing to work.

In the case of Hackage, the keys of its root key holders are contained in the haskell-infra/hackage-root-keys repository. The Hackage package index is signed. A signature is valid when three key holders have signed. The Hackage timestamp is also signed. A signature is valid when one key holder has signed.

If the hackage-security key is absent, the Hackage Security configuration will default to that for the official Hackage server.

key-threshold specifies the minimum number of keyholders that must have signed the package index for it to be considered valid.

ignore-expiry specifies whether or not the expiration of timestamps should be ignored.



Deprecated in favour of package-index, which takes precedence if present.


- download-prefix:
    - 0a5c7ea47cd1b15f01f5f51a33adda7e655bc0f0b0615baa8e271f4c3351e21d
    - 1ea9ba32c526d1cc91ab5e5bd364ec5e9e8cb67179a471872f6e26f0ae773d42
    - 2c6c3627bd6c982990239487f1abd02e08a02e6cf16edb105a8012d444d870c3
    - 51f0161b906011b52c6613376b1ae937670da69322113a246a09f807c62f6921
    - fe331502606802feac15e514d9b9ea83fee8b6ffef71335479a2e68d84adc6b0
    key-threshold: 3
    ignore-expiry: true


Before Stack 2.1.3, the default for ignore-expiry was false. For more information, see issue #4928.


Before Stack 2.1.1, Stack had a different approach to package-indices. For more information, see issue #4137.

Specify the package index. For further information, see the package-index documentation.


Default: none

Command line equivalent (takes precedence): stack sdist --pvp-bounds option or stack upload --pvp-bounds option


As of Stack 1.6.0, this feature does not reliably work, due to issues with the Cabal library's printer. Stack will generate a warning when a lossy conversion occurs, in which case you may need to disable this setting. For further information, see issue #3550.

When using the sdist and upload commands, this setting determines whether the Cabal file's dependencies should be modified to reflect PVP lower and upper bounds.

Basic use

Values are none (unchanged), upper (add upper bounds), lower (add lower bounds), and both (and upper and lower bounds). The algorithm it follows is:

  • If an upper or lower bound already exists on a dependency, it's left alone
  • When adding a lower bound, we look at the current version specified by stack.yaml, and set it as the lower bound (e.g., foo >= 1.2.3)
  • When adding an upper bound, we require less than the next major version (e.g., foo < 1.3)
pvp-bounds: none

For further information, see the announcement blog post.

Use with Cabal file revisions


Each of the values listed above supports adding -revision to the end of the value, e.g. pvp-bounds: both-revision. This means that, when uploading to Hackage, Stack will first upload your tarball with an unmodified Cabal file, and then upload a Cabal file revision with the PVP bounds added.

This can be useful - especially combined with the Stackage no-revisions feature - as a method to ensure PVP compliance without having to proactively fix bounds issues for Stackage maintenance.



When Stack notices that a new version of Stack is available, should it notify the user?

recommend-stack-upgrade: true


Default: false

Should we rebuild a package when its GHC options change? Before Stack 0.1.6, this was a non-configurable true. However, in most cases, the flag is used to affect optimization levels and warning behavior, for which GHC itself doesn't actually recompile the modules anyway. Therefore, the new behavior is to not recompile on an options change, but this behavior can be changed back with the following:

rebuild-ghc-options: true


Default: "-any"

Require a version of Stack within the specified range (cabal-style) to be used for this project. Example: require-stack-version: "== 0.1.*"



Default: true

Controls whether, when using stack upload, the user's Hackage username and password are stored in a local file.

save-hackage-creds: true


The setup-info dictionary specifies download locations for tools to be installed during set-up, such as GHC or, on Windows, 7z and MSYS2. The dictionary maps ('Tool', 'Platform', 'Version') to the location where it can be obtained. For example, mapping (GHC, 64-bit Windows, 9.2.3) to the URL hosting the archive file for GHC's installation.

Possible usages of this configuration option are:

  1. Using Stack offline or behind a firewall.
  2. Extending the tools known to Stack, such as cutting-edge versions of GHC or builds for custom Linux distributions (for use with the ghc-variant option).

By default, Stack obtains the dictionary from stack-setup-2.yaml.

The setup-info dictionary is constructed in the following order:

  1. setup-info in the YAML configuration - inline configuration
  2. --setup-info-yaml command line arguments - URLs or paths. Multiple locations may be specified.
  3. setup-info-locations in the YAML configuration - URLs or paths. See further below.

The format of this key is the same as in the default stack-setup-2.yaml. For example, GHC 9.2.3 of custom variant myvariant (see further below) on 64-bit Windows:

        url: ""

'Platforms' are pairs of an operating system and a machine architecture (for example, 32-bit i386 or 64-bit x86-64) (represented by the Cabal.Distribution.Systems.Platform type). Stack currently (version UNRELEASED) supports the following pairs in the format of the setup-info key:

Operating system I386 arch X86_64 arch Other machine architectures
Linux linux32 linux64 AArch64: linux-aarch64, Arm: linux-armv7, Sparc: linux-sparc
OSX macosx macosx
Windows windows32 windows64
FreeBSD freebsd32 freebsd64 AArch64: freebsd-aarch64
OpenBSD openbsd32 openbsd64

For GHC, the distinguishing 'Version' in the key format includes a 'tag' for any (optional) GHC variant (see ghc-variant) and a further 'tag' for any (optional) specialised GHC build (see ghc-build).

The optional variant 'tag' is either -integersimple or -custom-<custom_variant_name>.

For example, for GHC 9.0.2 of specialised GHC build tinfo6 on x86_64 Linux:

        url: ""
        content-length: 237286244
        sha1: affc2aaa3e6a1c446698a884f56a0a13e57f00b4
        sha256: b2670e9f278e10355b0475c2cc3b8842490f1bca3c70c306f104aa60caff37b0

On Windows, the required 7z executable and DLL tools are represented in the format of the setup-info key simply by sevenzexe-info and sevenzdll-info.

This configuration adds the specified setup information metadata to the default. Specifying this configuration does not prevent the default stack-setup-2.yaml from being consulted as a fallback. If, however, you need to replace the default setup-info dictionary, use the following:

setup-info-locations: []



Command line equivalent (takes precedence): --setup-info-yaml option

By way of introduction, see the setup-info option. This option specifies the location(s) of setup-info dictionaries.

The first location which provides a dictionary that specifies the location of a tool - ('Tool', 'Platform', 'Version') - takes precedence. For example, you can extend the default tools, with a fallback to the default setup-info location, as follows:

- C:/stack-offline/my-stack-setup.yaml
- relative/inside/my/project/setup-info.yaml
- \\smbShare\stack\my-stack-setup.yaml
# Fallback to the default location

Stack only refers to the default setup-info location if no locations are specified in the setup-info-locations configuration or on the command line using the --setup-info-yaml option.

For example, both of the following will cause stack setup not to consult the default setup-info location:

- C:/stack-offline/my-stack-setup.yaml


setup-info-locations: []

Relative paths are resolved relative to the stack.yaml file (either the one in the local project or the global stack.yaml).

Relative paths may also be used for the installation paths to tools (such as GHC or 7z). This allows vendoring the tools inside a monorepo (a single repository storing many projects). For example:

Directory structure:

- src/
- installs/
  - my-stack-setup.yaml
  - 7z.exe
  - 7z.dll
  - ghc-9.2.3.tar.xz
- stack.yaml

In the project's stack.yaml:

- installs/my-stack-setup.yaml

In installs/my-stack-setup.yaml:

  url: "installs/7z.exe"

  url: "installs/7z.dll"

      url: "installs/ghc-9.2.3.tar.xz"


Default: false

Command line equivalent (takes precedence): --[no-]skip-ghc-check flag

Should we skip the check to confirm that your system GHC version (on the PATH) matches what your project expects?


Restrictions: Windows systems only

Default: false

Command line equivalent (takes precedence): --[no-]skip-msys flag

Skips checking for and installing MSYS2 when stack is Setting up the environment. This usually doesn't make sense in project-level configurations, just in config.yaml.

skip-msys: true



Default: (as set in the pantry library)

Command line equivalent (takes precedence): --snapshot-location-base option

Sets the base location of the LTS Haskell or Stackage Nightly snapshots.

For example:


has the following effect:

  • lts-X.Y expands to
  • nightly-YYYY-MM-DD expands to

This key is convenient in setups that restrict access to GitHub, for instance closed corporate setups. In this setting, it is common for the development environment to have general access to the internet, but not for testing/building environments. To avoid the firewall, one can run a local snapshots mirror and then use a custom snapshot-location-base in the closed environments only.


Command line equivalent (takes precedence): --stack-colors option

Stack uses styles to format some of its output. The default styles do not work well with every terminal theme. This option specifies Stack's output styles, allowing new styles to replace the defaults. The option is used as stack-colors: <STYLES>, where <STYLES> is a colon-delimited sequence of key=value, 'key' is a style name and 'value' is a semicolon-delimited list of 'ANSI' SGR (Select Graphic Rendition) control codes (in decimal). Use the command stack ls stack-colors --basic to see the current sequence.

The 'ANSI' standards refer to (1) standard ECMA-48 'Control Functions for Coded Character Sets' (5th edition, 1991); (2) extensions in ITU-T Recommendation (previously CCITT Recommendation) T.416 (03/93) 'Information Technology – Open Document Architecture (ODA) and Interchange Format: Character Content Architectures' (also published as ISO/IEC International Standard 8613-6); and (3) further extensions used by 'XTerm', a terminal emulator for the X Window System. The 'ANSI' SGR codes are described in a Wikipedia article and those codes supported on current versions of Windows in Microsoft's documentation.

For example, users of the popular Solarized Dark terminal theme might wish to set the styles as follows:

stack-colors: error=31:good=32:shell=35:dir=34:recommendation=32:target=95:module=35:package-component=95:secondary=92:highlight=32
In respect of styles used in verbose output, some of that output occurs before the configuration file is processed.

(The British English spelling (colour) is also accepted. In YAML configuration files, the American spelling is the alternative that has priority.)



Default (official distributed binaries): false

Default (built from source): true

Turns on a mode where some messages are printed at WARN level instead of DEBUG level, especially useful for developers of Stack itself.

stack-developer-mode: false


Default: false, unless the Docker or Nix integration is enabled.

Command line equivalent (takes precedence): --[no-]system-ghc flag

Enables or disables using the GHC available on the PATH. (Make sure PATH is explicit, i.e., don't use ~.) Useful to enable if you want to save the time, bandwidth or storage space needed to setup an isolated GHC.

In a Nix-enabled configuration, Stack is incompatible with system-ghc: false.

# Turn on system GHC
system-ghc: true


Command line equivalent (takes precedence): stack new --param <key>:<value> (or -p) option

Templates used with stack new have a number of parameters that affect the generated code. These can be set for all new projects you create. The result of them can be observed in the generated LICENSE and Cabal files. The value for all of these parameters must be strings.

The parameters are: author-email, author-name, category, copyright, year and github-username.

  • author-email - sets the maintainer property in Cabal
  • author-name - sets the author property in Cabal and the name used in LICENSE
  • category - sets the category property in Cabal. This is used in Hackage. For examples of categories see Packages by category. It makes sense for category to be set on a per project basis because it is uncommon for all projects a user creates to belong to the same category. The category can be set per project by passing -p "category:value" to the stack new command.
  • copyright - sets the copyright property in Cabal. It is typically the name of the holder of the copyright on the package and the year(s) from which copyright is claimed. For example: Copyright (c) 2006-2007 Joe Bloggs
  • year - if copyright is not specified, year and author-name are used to generate the copyright property in Cabal. If year is not specified, it defaults to the current year.
  • github-username - used to generate homepage and source-repository in Cabal. For instance github-username: myusername and stack new my-project new-template would result:

source-repository head
  type: git

These properties can be set in config.yaml as follows:

    author-name: Your Name
    category: Your Projects Category
    copyright: 'Copyright (c) 2022 Your Name'
    github-username: yourusername

Additionally, stack new can automatically initialize source control repositories in the directories it creates. Source control tools can be specified with the scm-init option. At the moment, only git is supported.

  scm-init: git




Customize the URLs where Stack looks for snapshot build plans.


Command line equivalent (takes precedence): --with-gcc option

Specify a path to GCC explicitly, rather than relying on the normal path resolution.

with-gcc: /usr/local/bin/gcc-5


Command line equivalent (takes precedence): --with-hpack option

Use an Hpack executable, rather than Stack's in-built version of the Hpack functionality.

with-hpack: /usr/local/bin/hpack


Default: .stack-work

Command line equivalent (takes precedence): --work-dir option

Environment variable alternative (lowest precedence): STACK_WORK

work-dir specifies the path of Stack's work directory, within a local project or package directory. The path must be a relative one, relative to the root directory of the project or package. The relative path cannot include a .. (parent directory) component.

Customisation scripts

GHC installation customisation


On Unix-like operating systems and Windows, Stack's installation procedure can be fully customised by placing a sh shell script (a 'hook') in the Stack root directory at hooks/ On Unix-like operating systems, the script file must be made executable. The script is run by the sh application (which is provided by MSYS2 on Windows).

The script must return an exit code of 0 and the standard output must be the absolute path to the GHC binary that was installed. Otherwise Stack will ignore the script and possibly fall back to its own installation procedure.

The script is not run when system-ghc: true.

When install-ghc: false, the script is still run, which allows you to ensure that only your script will install GHC and Stack won't default to its own installation logic, even when the script fails.

The following environment variables are always available to the script:

  • HOOK_GHC_TYPE = "bindist" | "git" | "ghcjs"

For "bindist", additional variables are:

  • HOOK_GHC_VERSION = <ver>

For "git", additional variables are:

  • HOOK_GHC_COMMIT = <commit>
  • HOOK_GHC_FLAVOR = <flavor>

For "ghcjs", additional variables are:

  • HOOK_GHC_VERSION = <ver>

An example script is:


set -eu

case $HOOK_GHC_TYPE in
        # install GHC here, not printing to stdout, e.g.:
        #   command install $HOOK_GHC_VERSION >/dev/null
        >&2 echo "Hook doesn't support installing from source"
        exit 1
        >&2 echo "Unsupported GHC installation type: $HOOK_GHC_TYPE"
        exit 2

echo "location/to/ghc/executable"

If the following script is installed by GHCup, GHCup makes use of it, so that if Stack needs a version of GHC, GHCup takes over obtaining and installing that version:


set -eu

case $HOOK_GHC_TYPE in
        ghcdir=$(ghcup whereis --directory ghc "$HOOK_GHC_VERSION" || ghcup run --ghc "$HOOK_GHC_VERSION" --install) || exit 3
        printf "%s/ghc" "${ghcdir}"
        # TODO: should be somewhat possible
        >&2 echo "Hook doesn't support installing from source"
        exit 1
        >&2 echo "Unsupported GHC installation type: $HOOK_GHC_TYPE"
        exit 2