10. Project.toml and Manifest.toml

Two files that are central to Pkg are Project.toml and Manifest.toml. Project.toml and Manifest.toml are written in TOML (hence the .toml extension) and include information about dependencies, versions, package names, UUIDs etc.

Project.toml

The project file describes the project on a high level, for example, the package/project dependencies and compatibility constraints are listed in the project file. The file entries are described below.

The authors field

For a package, the optional authors field is a list of strings describing the package authors, in the form NAME <EMAIL>. For example:

authors = ["Some One <someone@email.com>",
           "Foo Bar <foo@bar.com>"]

The name field

The name of the package/project is determined by the name field, for example:

name = "Example"

The name must be a valid identifier (a sequence of Unicode characters that does not start with a number and is neither true nor false). For packages, it is recommended to follow the package naming rules. The name field is mandatory for packages.

The uuid field

uuid is a string with a universally unique identifier for the package/project, for example:

uuid = "7876af07-990d-54b4-ab0e-23690620f79a"

The uuid field is mandatory for packages.

The version field

version is a string with the version number for the package/project. It should consist of three numbers, major version, minor version, and patch number, separated with a ., for example:

version = "1.2.5"

Julia uses Semantic Versioning (SemVer) and the version field should follow SemVer. The basic rules are:

• Before 1.0.0, anything goes, but when you make breaking changes the minor version should be incremented.
• After 1.0.0 only make breaking changes when incrementing the major version.
• After 1.0.0 no new public API should be added without incrementing the minor version. This includes, in particular, new types, functions, methods, and method overloads, from Base or other packages.

See also the section on Compatibility.

Note that Pkg.jl deviates from the SemVer specification when it comes to versions pre-1.0.0. See the section on pre-1.0 behavior for more details.

The [deps] section

All dependencies of the package/project are listed in the [deps] section. Each dependency is listed as a name-uuid pair, for example:

[deps]
Example = "7876af07-990d-54b4-ab0e-23690620f79a"
Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"

Typically it is not needed to manually add entries to the [deps] section; this is instead handled by Pkg operations such as add.

The [sources] section

Specifiying a path or repo (+ branch) for a dependency is done in the [sources] section. These are especially useful for controlling unregistered dependencies without having to bundle a corresponding manifest file.

[sources]
Example = {url = "https://github.com/JuliaLang/Example.jl", rev = "custom_branch"}
SomeDependency = {path = "deps/SomeDependency.jl"}

Note that this information is only used when this environment is active, i.e. it is not used if this project is a package that is being used as a dependency.

The [compat] section

Compatibility constraints for the dependencies listed under [deps] can be listed in the [compat] section. Example:

[deps]
Example = "7876af07-990d-54b4-ab0e-23690620f79a"

[compat]
Example = "1.2"

The Compatibility section describes the different possible compatibility constraints in detail. It is also possible to list constraints on julia itself, although julia is not listed as a dependency in the [deps] section:

[compat]
julia = "1.1"

The [workspace] section

A project file can define a workspace by giving a set of projects that is part of that workspace. Each project in a workspace can include their own dependencies, compatibility information, and even function as full packages.

When the package manager resolves dependencies, it considers the requirements of all the projects in the workspace. The compatible versions identified during this process are recorded in a single manifest file located next to the base project file.

A workspace is defined in the base project by giving a list of the projects in it:

[workspace]
projects = ["test", "docs", "benchmarks", "PrivatePackage"]

This structure is particularly beneficial for developers using a monorepo approach, where a large number of unregistered packages may be involved. It's also useful for adding documentation or benchmarks to a package by including additional dependencies beyond those of the package itself.

Workspace can be nested: a project that itself defines a workspace can also be part of another workspace. In this case, the workspaces are "merged" with a single manifest being stored alongside the "root project" (the project that doesn't have another workspace including it).

Manifest.toml

The manifest file is an absolute record of the state of the packages in the environment. It includes exact information about (direct and indirect) dependencies of the project. Given a Project.toml + Manifest.toml pair, it is possible to instantiate the exact same package environment, which is very useful for reproducibility. For the details, see Pkg.instantiate.

Different Manifests for Different Julia versions

Starting from Julia v1.11, there is an option to name manifest files in the format Manifest-v{major}.{minor}.toml. Julia will then preferentially use the version-specific manifest file if available. For example, if both Manifest-v1.11.toml and Manifest.toml exist, Julia 1.11 will prioritize using Manifest-v1.11.toml. However, Julia versions 1.10, 1.12, and all others will default to using Manifest.toml. This feature allows for easier management of different instantiated versions of dependencies for various Julia versions. Note that there can only be one Project.toml file. While Manifest-v{major}.{minor}.toml files are not automatically created by Pkg, users can manually rename a Manifest.toml file to match the versioned format, and Pkg will subsequently maintain it through its operations.

Manifest.toml entries

There are three top-level entries in the manifest which could look like this:

julia_version = "1.8.2"
manifest_format = "2.0"
project_hash = "4d9d5b552a1236d3c1171abf88d59da3aaac328a"

This shows the Julia version the manifest was created on, the "format" of the manifest and a hash of the project file, so that it is possible to see when the manifest is stale compared to the project file.

Each dependency has its own section in the manifest file, and its content varies depending on how the dependency was added to the environment. Every dependency section includes a combination of the following entries:

• uuid: the UUID for the dependency, for example uuid = "7876af07-990d-54b4-ab0e-23690620f79a".
• deps: a vector listing the dependencies of the dependency, for example deps = ["Example", "JSON"].
• version: a version number, for example version = "1.2.6".
• path: a file path to the source code, for example path = /home/user/Example.
• repo-url: a URL to the repository where the source code was found, for example repo-url = "https://github.com/JuliaLang/Example.jl.git".
• repo-rev: a git revision, for example a branch repo-rev = "master" or a commit repo-rev = "66607a62a83cb07ab18c0b35c038fcd62987c9b1".
• git-tree-sha1: a content hash of the source tree, for example git-tree-sha1 = "ca3820cc4e66f473467d912c4b2b3ae5dc968444".

Added package

When a package is added from a package registry, for example by invoking pkg> add Example or with a specific version pkg> add Example@1.2, the resulting Manifest.toml entry looks like:

[[deps.Example]]
deps = ["DependencyA", "DependencyB"]
git-tree-sha1 = "8eb7b4d4ca487caade9ba3e85932e28ce6d6e1f8"
uuid = "7876af07-990d-54b4-ab0e-23690620f79a"
version = "1.2.3"

Note, in particular, that no repo-url is present, since that information is included in the registry where this package was found.

Added package by branch

The resulting dependency section when adding a package specified by a branch, e.g. pkg> add Example#master or pkg> add https://github.com/JuliaLang/Example.jl.git, looks like:

[[deps.Example]]
deps = ["DependencyA", "DependencyB"]
git-tree-sha1 = "54c7a512469a38312a058ec9f429e1db1f074474"
repo-rev = "master"
repo-url = "https://github.com/JuliaLang/Example.jl.git"
uuid = "7876af07-990d-54b4-ab0e-23690620f79a"
version = "1.2.4"

Note that both the branch we are tracking (master) and the remote repository url ("https://github.com/JuliaLang/Example.jl.git") are stored in the manifest.

Added package by commit

The resulting dependency section when adding a package specified by a commit, e.g. pkg> add Example#cf6ba6cc0be0bb5f56840188563579d67048be34, looks like:

[[deps.Example]]
deps = ["DependencyA", "DependencyB"]
git-tree-sha1 = "54c7a512469a38312a058ec9f429e1db1f074474"
repo-rev = "cf6ba6cc0be0bb5f56840188563579d67048be34"
repo-url = "https://github.com/JuliaLang/Example.jl.git"
uuid = "7876af07-990d-54b4-ab0e-23690620f79a"
version = "1.2.4"

The only difference from tracking a branch is the content of repo-rev.

Developed package

The resulting dependency section when adding a package with develop, e.g. pkg> develop Example or pkg> develop /path/to/local/folder/Example, looks like:

[[deps.Example]]
deps = ["DependencyA", "DependencyB"]
path = "/home/user/.julia/dev/Example/"
uuid = "7876af07-990d-54b4-ab0e-23690620f79a"
version = "1.2.4"

Note that the path to the source code is included, and changes made to that source tree is directly reflected.

Pinned package

Pinned packages are also recorded in the manifest file; the resulting dependency section e.g. pkg> add Example; pin Example looks like:

[[deps.Example]]
deps = ["DependencyA", "DependencyB"]
git-tree-sha1 = "54c7a512469a38312a058ec9f429e1db1f074474"
pinned = true
uuid = "7876af07-990d-54b4-ab0e-23690620f79a"
version = "1.2.4"

The only difference is the addition of the pinned = true entry.

Multiple packages with the same name

Julia differentiates packages based on UUID, which means that the name alone is not enough to identify a package. It is possible to have multiple packages in the same environment with the same name, but with different UUID. In such a situation the Manifest.toml file looks a bit different. Consider for example the situation where you have added A and B to your environment, and the Project.toml file looks as follows:

[deps]
A = "ead4f63c-334e-11e9-00e6-e7f0a5f21b60"
B = "edca9bc6-334e-11e9-3554-9595dbb4349c"

If A now depends on B = "f41f7b98-334e-11e9-1257-49272045fb24", i.e. another package named B there will be two different B packages in the Manifest.toml file. In this case, the full Manifest.toml file, with git-tree-sha1 and version fields removed for clarity, looks like this:

[[deps.A]]
uuid = "ead4f63c-334e-11e9-00e6-e7f0a5f21b60"

    [deps.A.deps]
    B = "f41f7b98-334e-11e9-1257-49272045fb24"

[[deps.B]]
uuid = "f41f7b98-334e-11e9-1257-49272045fb24"
[[deps.B]]
uuid = "edca9bc6-334e-11e9-3554-9595dbb4349c"

There is now an array of the two B packages, and the [deps] section for A has been expanded to be explicit about which B package A depends on.