# [**10.** `Project.toml` and `Manifest.toml`](@id Project-and-Manifest)

Two files that are central to Pkg are `Project.toml` and `Manifest.toml`. `Project.toml`
and `Manifest.toml` are written in [TOML](https://github.com/toml-lang/toml) (hence the
`.toml` extension) and include information about dependencies, versions, package names,
UUIDs etc.

!!! note
    The `Project.toml` and `Manifest.toml` files are not only used by the package manager;
    they are also used by Julia's code loading, and determine e.g. what `using Example`
    should do. For more details see the section about
    [Code Loading](https://docs.julialang.org/en/v1/manual/code-loading/)
    in the Julia manual.


## `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:
```toml
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:
```toml
name = "Example"
```
The name must be a valid [identifier](https://docs.julialang.org/en/v1/base/base/#Base.isidentifier)
(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 guidelines](@ref Package-naming-guidelines). The `name` field is mandatory
for packages.


### The `uuid` field

`uuid` is a string with a [universally unique identifier]
(https://en.wikipedia.org/wiki/Universally_unique_identifier) for the package/project, for example:
```toml
uuid = "7876af07-990d-54b4-ab0e-23690620f79a"
```
The `uuid` field is mandatory for packages.

!!! note
    It is recommended that `UUIDs.uuid4()` is used to generate random UUIDs.


### 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:
```toml
version = "1.2.5"
```
Julia uses [Semantic Versioning](https://semver.org/) (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](@ref).

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](@ref compat-pre-1.0) 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:

```toml
[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 `[compat]` section

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

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

[compat]
Example = "1.2"
```

The [Compatibility](@ref) 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:

```toml
[compat]
julia = "1.1"
```


## `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`](@ref).

!!! note
    The `Manifest.toml` file is generated and maintained by Pkg and, in general, this file
    should *never* be modified manually.


### `Manifest.toml` entries

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

```toml
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](https://en.wikipedia.org/wiki/Universally_unique_identifier)
  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:

```toml
[[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:

```toml
[[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:

```toml
[[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:

```toml
[[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:

```toml
[[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:

```toml
[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:

```toml
[[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.
