The Manifest Format

The Cargo.toml file for each package is called its manifest. It is written in the TOML format. It contains metadata that is needed to compile the package. Checkout the cargo locate-project section for more detail on how cargo finds the manifest file.

Every manifest file consists of the following sections:

The [package] section

The first section in a Cargo.toml is [package].

[package]
name = "hello_world" # the name of the package
version = "0.1.0"    # the current version, obeying semver
authors = ["Alice <a@example.com>", "Bob <b@example.com>"]

The only fields required by Cargo are name and version. If publishing to a registry, the registry may require additional fields. See the notes below and the publishing chapter for requirements for publishing to crates.io.

The name field

The package name is an identifier used to refer to the package. It is used when listed as a dependency in another package, and as the default name of inferred lib and bin targets.

The name must use only alphanumeric characters or - or _, and cannot be empty.

Note that cargo new and cargo init impose some additional restrictions on the package name, such as enforcing that it is a valid Rust identifier and not a keyword. crates.io imposes even more restrictions, such as:

  • Only ASCII characters are allowed.
  • Do not use reserved names.
  • Do not use special Windows names such as “nul”.
  • Use a maximum of 64 characters of length.

The version field

Cargo bakes in the concept of Semantic Versioning, so make sure you follow some basic rules:

  • Before you reach 1.0.0, anything goes, but if you make breaking changes, increment the minor version. In Rust, breaking changes include adding fields to structs or variants to enums.
  • After 1.0.0, only make breaking changes when you increment the major version. Don’t break the build.
  • After 1.0.0, don’t add any new public API (no new pub anything) in patch-level versions. Always increment the minor version if you add any new pub structs, traits, fields, types, functions, methods or anything else.
  • Use version numbers with three numeric parts such as 1.0.0 rather than 1.0.

See the Resolver chapter for more information on how Cargo uses versions to resolve dependencies, and for guidelines on setting your own version. See the SemVer compatibility chapter for more details on exactly what constitutes a breaking change.

This field is optional and defaults to 0.0.0. The field is required for publishing packages.

The authors field

The optional authors field lists in an array the people or organizations that are considered the “authors” of the package. The exact meaning is open to interpretation — it may list the original or primary authors, current maintainers, or owners of the package. An optional email address may be included within angled brackets at the end of each author entry.

[package]
# ...
authors = ["Graydon Hoare", "Fnu Lnu <no-reply@rust-lang.org>"]

This field is only surfaced in package metadata and in the CARGO_PKG_AUTHORS environment variable within build.rs. It is not displayed in the crates.io user interface.

Warning: Package manifests cannot be changed once published, so this field cannot be changed or removed in already-published versions of a package.

The edition field

The edition key is an optional key that affects which Rust Edition your package is compiled with. Setting the edition key in [package] will affect all targets/crates in the package, including test suites, benchmarks, binaries, examples, etc.

[package]
# ...
edition = '2021'

Most manifests have the edition field filled in automatically by cargo new with the latest stable edition. By default cargo new creates a manifest with the 2021 edition currently.

If the edition field is not present in Cargo.toml, then the 2015 edition is assumed for backwards compatibility. Note that all manifests created with cargo new will not use this historical fallback because they will have edition explicitly specified to a newer value.

The rust-version field

The rust-version field is an optional key that tells cargo what version of the Rust language and compiler your package can be compiled with. If the currently selected version of the Rust compiler is older than the stated version, cargo will exit with an error, telling the user what version is required.

The first version of Cargo that supports this field was released with Rust 1.56.0. In older releases, the field will be ignored, and Cargo will display a warning.

[package]
# ...
rust-version = "1.56"

The Rust version must be a bare version number with two or three components; it cannot include semver operators or pre-release identifiers. Compiler pre-release identifiers such as -nightly will be ignored while checking the Rust version. The rust-version must be equal to or newer than the version that first introduced the configured edition.

The rust-version may be ignored using the --ignore-rust-version option.

Setting the rust-version key in [package] will affect all targets/crates in the package, including test suites, benchmarks, binaries, examples, etc.

To find the minimum rust-version compatible with your project, you can use third-party tools like cargo-msrv.

When used on packages that get published, we recommend verifying the rust-version.

The description field

The description is a short blurb about the package. crates.io will display this with your package. This should be plain text (not Markdown).

[package]
# ...
description = "A short description of my package"

Note: crates.io requires the description to be set.

The documentation field

The documentation field specifies a URL to a website hosting the crate’s documentation. If no URL is specified in the manifest file, crates.io will automatically link your crate to the corresponding docs.rs page when the documentation has been built and is available (see docs.rs queue).

[package]
# ...
documentation = "https://docs.rs/bitflags"

The readme field

The readme field should be the path to a file in the package root (relative to this Cargo.toml) that contains general information about the package. This file will be transferred to the registry when you publish. crates.io will interpret it as Markdown and render it on the crate’s page.

[package]
# ...
readme = "README.md"

If no value is specified for this field, and a file named README.md, README.txt or README exists in the package root, then the name of that file will be used. You can suppress this behavior by setting this field to false. If the field is set to true, a default value of README.md will be assumed.

The homepage field

The homepage field should be a URL to a site that is the home page for your package.

[package]
# ...
homepage = "https://serde.rs"

A value should only be set for homepage if there is a dedicated website for the crate other than the source repository or API documentation. Do not make homepage redundant with either the documentation or repository values.

The repository field

The repository field should be a URL to the source repository for your package.

[package]
# ...
repository = "https://github.com/rust-lang/cargo"

The license and license-file fields

The license field contains the name of the software license that the package is released under. The license-file field contains the path to a file containing the text of the license (relative to this Cargo.toml).

crates.io interprets the license field as an SPDX 2.3 license expression. The name must be a known license from the SPDX license list 3.20. See the SPDX site for more information.

SPDX license expressions support AND and OR operators to combine multiple licenses.1

[package]
# ...
license = "MIT OR Apache-2.0"

Using OR indicates the user may choose either license. Using AND indicates the user must comply with both licenses simultaneously. The WITH operator indicates a license with a special exception. Some examples:

  • MIT OR Apache-2.0
  • LGPL-2.1-only AND MIT AND BSD-2-Clause
  • GPL-2.0-or-later WITH Bison-exception-2.2

If a package is using a nonstandard license, then the license-file field may be specified in lieu of the license field.

[package]
# ...
license-file = "LICENSE.txt"

Note: crates.io requires either license or license-file to be set.

1

Previously multiple licenses could be separated with a /, but that usage is deprecated.

The keywords field

The keywords field is an array of strings that describe this package. This can help when searching for the package on a registry, and you may choose any words that would help someone find this crate.

[package]
# ...
keywords = ["gamedev", "graphics"]

Note: crates.io allows a maximum of 5 keywords. Each keyword must be ASCII text, have at most 20 characters, start with an alphanumeric character, and only contain letters, numbers, _, - or +.

The categories field

The categories field is an array of strings of the categories this package belongs to.

categories = ["command-line-utilities", "development-tools::cargo-plugins"]

Note: crates.io has a maximum of 5 categories. Each category should match one of the strings available at https://crates.io/category_slugs, and must match exactly.

The workspace field

The workspace field can be used to configure the workspace that this package will be a member of. If not specified this will be inferred as the first Cargo.toml with [workspace] upwards in the filesystem. Setting this is useful if the member is not inside a subdirectory of the workspace root.

[package]
# ...
workspace = "path/to/workspace/root"

This field cannot be specified if the manifest already has a [workspace] table defined. That is, a crate cannot both be a root crate in a workspace (contain [workspace]) and also be a member crate of another workspace (contain package.workspace).

For more information, see the workspaces chapter.

The build field

The build field specifies a file in the package root which is a build script for building native code. More information can be found in the build script guide.

[package]
# ...
build = "build.rs"

The default is "build.rs", which loads the script from a file named build.rs in the root of the package. Use build = "custom_build_name.rs" to specify a path to a different file or build = false to disable automatic detection of the build script.

The links field specifies the name of a native library that is being linked to. More information can be found in the links section of the build script guide.

For example, a crate that links a native library called “git2” (e.g. libgit2.a on Linux) may specify:

[package]
# ...
links = "git2"

The exclude and include fields

The exclude and include fields can be used to explicitly specify which files are included when packaging a project to be published, and certain kinds of change tracking (described below). The patterns specified in the exclude field identify a set of files that are not included, and the patterns in include specify files that are explicitly included. You may run cargo package --list to verify which files will be included in the package.

[package]
# ...
exclude = ["/ci", "images/", ".*"]

[package]
# ...
include = ["/src", "COPYRIGHT", "/examples", "!/examples/big_example"]

The default if neither field is specified is to include all files from the root of the package, except for the exclusions listed below.

If include is not specified, then the following files will be excluded:

  • If the package is not in a git repository, all “hidden” files starting with a dot will be skipped.
  • If the package is in a git repository, any files that are ignored by the gitignore rules of the repository and global git configuration will be skipped.

Regardless of whether exclude or include is specified, the following files are always excluded:

  • Any sub-packages will be skipped (any subdirectory that contains a Cargo.toml file).
  • A directory named target in the root of the package will be skipped.

The following files are always included:

  • The Cargo.toml file of the package itself is always included, it does not need to be listed in include.
  • A minimized Cargo.lock is automatically included if the package contains a binary or example target, see cargo package for more information.
  • If a license-file is specified, it is always included.

The options are mutually exclusive; setting include will override an exclude. If you need to have exclusions to a set of include files, use the ! operator described below.

The patterns should be gitignore-style patterns. Briefly:

  • foo matches any file or directory with the name foo anywhere in the package. This is equivalent to the pattern **/foo.
  • /foo matches any file or directory with the name foo only in the root of the package.
  • foo/ matches any directory with the name foo anywhere in the package.
  • Common glob patterns like *, ?, and [] are supported:
    • * matches zero or more characters except /. For example, *.html matches any file or directory with the .html extension anywhere in the package.
    • ? matches any character except /. For example, foo? matches food, but not foo.
    • [] allows for matching a range of characters. For example, [ab] matches either a or b. [a-z] matches letters a through z.
  • **/ prefix matches in any directory. For example, **/foo/bar matches the file or directory bar anywhere that is directly under directory foo.
  • /** suffix matches everything inside. For example, foo/** matches all files inside directory foo, including all files in subdirectories below foo.
  • /**/ matches zero or more directories. For example, a/**/b matches a/b, a/x/b, a/x/y/b, and so on.
  • ! prefix negates a pattern. For example, a pattern of src/*.rs and !foo.rs would match all files with the .rs extension inside the src directory, except for any file named foo.rs.

The include/exclude list is also used for change tracking in some situations. For targets built with rustdoc, it is used to determine the list of files to track to determine if the target should be rebuilt. If the package has a build script that does not emit any rerun-if-* directives, then the include/exclude list is used for tracking if the build script should be re-run if any of those files change.

The publish field

The publish field can be used to control which registries names the package may be published to:

[package]
# ...
publish = ["some-registry-name"]

To prevent a package from being published to a registry (like crates.io) by mistake, for instance to keep a package private in a company, you can omit the version field. If you’d like to be more explicit, you can disable publishing:

[package]
# ...
publish = false

If publish array contains a single registry, cargo publish command will use it when --registry flag is not specified.

The metadata table

Cargo by default will warn about unused keys in Cargo.toml to assist in detecting typos and such. The package.metadata table, however, is completely ignored by Cargo and will not be warned about. This section can be used for tools which would like to store package configuration in Cargo.toml. For example:

[package]
name = "..."
# ...

# Metadata used when generating an Android APK, for example.
[package.metadata.android]
package-name = "my-awesome-android-app"
assets = "path/to/static"

You’ll need to look in the documentation for your tool to see how to use this field. For Rust Projects that use package.metadata tables, see:

There is a similar table at the workspace level at workspace.metadata. While cargo does not specify a format for the content of either of these tables, it is suggested that external tools may wish to use them in a consistent fashion, such as referring to the data in workspace.metadata if data is missing from package.metadata, if that makes sense for the tool in question.

The default-run field

The default-run field in the [package] section of the manifest can be used to specify a default binary picked by cargo run. For example, when there is both src/bin/a.rs and src/bin/b.rs:

[package]
default-run = "a"

The lints section

Override the default level of lints from different tools by assigning them to a new level in a table, for example:

[lints.rust]
unsafe_code = "forbid"

This is short-hand for:

[lints.rust]
unsafe_code = { level = "forbid", priority = 0 }

level corresponds to the lint levels in rustc:

  • forbid
  • deny
  • warn
  • allow

priority is a signed integer that controls which lints or lint groups override other lint groups:

  • lower (particularly negative) numbers have lower priority, being overridden by higher numbers, and show up first on the command-line to tools like rustc

To know which table under [lints] a particular lint belongs under, it is the part before :: in the lint name. If there isn’t a ::, then the tool is rust. For example a warning about unsafe_code would be lints.rust.unsafe_code but a lint about clippy::enum_glob_use would be lints.clippy.enum_glob_use.

For example:

[lints.rust]
unsafe_code = "forbid"

[lints.clippy]
enum_glob_use = "deny"

Generally, these will only affect local development of the current package. Cargo only applies these to the current package and not to dependencies. As for dependents, Cargo suppresses lints from non-path dependencies with features like --cap-lints.

The [badges] section

The [badges] section is for specifying status badges that can be displayed on a registry website when the package is published.

Note: crates.io previously displayed badges next to a crate on its website, but that functionality has been removed. Packages should place badges in its README file which will be displayed on crates.io (see the readme field).

[badges]
# The `maintenance` table indicates the status of the maintenance of
# the crate. This may be used by a registry, but is currently not
# used by crates.io. See https://github.com/rust-lang/crates.io/issues/2437
# and https://github.com/rust-lang/crates.io/issues/2438 for more details.
#
# The `status` field is required. Available options are:
# - `actively-developed`: New features are being added and bugs are being fixed.
# - `passively-maintained`: There are no plans for new features, but the maintainer intends to
#   respond to issues that get filed.
# - `as-is`: The crate is feature complete, the maintainer does not intend to continue working on
#   it or providing support, but it works for the purposes it was designed for.
# - `experimental`: The author wants to share it with the community but is not intending to meet
#   anyone's particular use case.
# - `looking-for-maintainer`: The current maintainer would like to transfer the crate to someone
#   else.
# - `deprecated`: The maintainer does not recommend using this crate (the description of the crate
#   can describe why, there could be a better solution available or there could be problems with
#   the crate that the author does not want to fix).
# - `none`: Displays no badge on crates.io, since the maintainer has not chosen to specify
#   their intentions, potential crate users will need to investigate on their own.
maintenance = { status = "..." }

Dependency sections

See the specifying dependencies page for information on the [dependencies], [dev-dependencies], [build-dependencies], and target-specific [target.*.dependencies] sections.

The [profile.*] sections

The [profile] tables provide a way to customize compiler settings such as optimizations and debug settings. See the Profiles chapter for more detail.