[][src]Crate cargo_deny

❌ cargo-deny

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One of the key selling points of Rust is the ever growing and improving ecosystem of crates available that can be easily added to your project incredibly easily via cargo. This is great! However, the larger the project is and the more dependencies you have, the harder it is to keep track of certain things, especially as a project evolves over time, which is what cargo-deny tries to help you with.

  • Licenses - Configure which licenses are allowed
  • Bans - Configure whether certain crates are allowed to be in your dependency graph


  • cargo-deny check <license|all> - verify licenses for a crate graph
  • cargo-deny check <ban|all> - verify crate graph doesn't contain certain crates
  • cargo-deny list - list all of the licenses in a crate graph

Licenses - cargo-deny check license

One important aspect that one must always keep in mind when using code from other people is what the licensing of that code is and whether it fits the requirements of your project. Luckily, most of the crates in the Rust ecosystem tend to follow the example set forth by Rust itself, namely dual-license MIT OR Apache-2.0, but of course, that is not always the case.

So cargo-deny allows you to ensure that all of your dependencies meet the requirements you want.

  1. What happens when a crate is unlicensed? allow / deny / warn
  2. What happens when a crate's license can't be determined? allow / deny / warn
  3. Explicitly allow or deny 1 or more licenses.
  4. Skip checking certain crates as long as they still have the same license information.
  5. Ignore specific LICENSE* files. cargo-deny uses the askalono crate to parse and score license text as being a certain license, but some license text can be modified to such an extent that it makes it difficult to automatically determine it.

Example config

# If a crate doesn't have a license, error
unlicensed = "deny"
# If a crate has a LICENSE* file, but it can't be determined, error
unknown = "deny"
# We want really high confidence when inferring licenses from text
confidence_threshold = 0.92
# The only licenses we allow. These must be valid SPDX identifiers, at least syntactically,
# but nothing stops you from using your own license identifier for your private crates
allow = [
skip = [
    # ring has a rather complicated LICENSE file due to reasons spelled out
    # in said LICENSE file, but is basically OpenSSL for older parts, and ISC
    # for newer parts
    { name = "ring", licenses = [] },
    # webpki uses an ISC license but it only has a 0.83 confidence level
    { name = "webpki", licenses = [] },

name = "rustls"
license_files = [
    # This is a top-level LICENSE that just spells out the *actual* 3
    # licenses that can be used with the crate, which askalono is unable
    # to score
    { path = "LICENSE", hash = 0xe567c411 },

Crate bans - cargo-deny check ban

Use Case - Keeping certain crates out of your dependency graph

Sometimes, certain crates just don't fit in your project, so you have to remove them. However, nothing really stops them from sneaking back in due to small changes, like updating a crate to a new version that happens to add it as a dependency, or an existing dependency just changing what crates are included in the default feature set.

For example, we previously depended on OpenSSL as it is the "default" for many crates that deal with HTTP traffic. This was extremely annoying as it required us to have OpenSSL development libraries installed on Windows, for both individuals and CI. We moved all of our dependencies to use the much more streamlined native-tls and ring crates instead, and now we can make sure that OpenSSL doesn't return from the grave by being pulled in as a default feature of some future HTTP crate we might use.

  1. Dis/allow certain crates in your dependency graph.

Use Case - Get a handle on duplicate versions

One thing that is part of the tradeoff of being able to use so many crates, is that they all won't necessarily agree on what versions of a dependency they want to use, and cargo and rust will happily chug along compiling all of them. This is great when just trying out a new dependency as quickly as possible, but it does come with some long term costs. Crate fetch times (and disk space) are increased, but in particular, compile times, and ultimately your binary sizes, also increase. If you are made aware that you depend on multiple versions of the same crate, you at least have an opportunity to decide how you want to handle them.

  1. What happens when multiple versions of a crate are used? allow / deny / warn
  2. Skip certain versions of crates, sometimes you just need to wait for a crate to get a new release, or sometimes a little duplication is ok and not worth the effort to "fix", but you are at least aware of it and explicitly allowing it, rather than suffering in ignorance.
  3. The -g <path> cmd line option on the check subcommand instructs cargo-deny to create a dotgraph if multiple versions of a crate are detected and that isn't allowed. A single graph will be created for each crate, with each version as a terminating node in the graph with the full graph of crates that reference each version to more easily show you why a particular version is included. It also highlights the lowest version's path in red, and, if it differs from the lowest version, the "simplest" path is highlighted in blue.


Example Config

# Emit an error if we detect multiple versions of the same crate
multiple_versions = "deny"
deny = [
    # OpenSSL = Just Say No.
    { name = "openssl" },
skip = [
    # The issue where mime_guess is using a really old version of
    # unicase has been fixed, it just needs to be released
    # https://github.com/sfackler/rust-phf/issues/143
    { name = "unicase", version = "=1.4.2" },
    # rayon/rayon-core use very old versions of crossbeam crates,
    # so skip them for now until rayon updates them
    { name = "crossbeam-deque", version = "=0.2.0" },
    { name = "crossbeam-epoch", version = "=0.3.1" },
    { name = "crossbeam-utils", version = "=0.2.2" },
    # tokio-reactor, wasmer, and winit all use an older version
    # of parking_lot
    { name = "parking_lot", version = "=0.7.1" },
    { name = "parking_lot_core", version = "=0.4.0" },
    { name = "lock_api", version = "=0.1.5" },
    # rand_core depends on a newever version of itself...
    { name = "rand_core", version = "=0.3.1" },
    # lots of transitive dependencies use the pre-1.0 version
    # of scopeguard
    { name = "scopeguard", version = "=0.3.3" },
    # tons of transitive dependencies use this older winapi version
    { name = "winapi", version = "=0.2.8" },

CI Usage

cargo-deny is primarily meant to be used in your CI so it can do automatic verification for all your changes, for an example of this, you can look at the self check job for this repository, which just checks cargo-deny itself using the deny.toml config.

List - cargo-deny list

Similarly to cargo-license, print out the licenses and crates that use them.

  • layout = license, format = human (default)


  • layout = crate, format = human


  • layout = license, format = json


  • layout = license, format = tsv



Licensed under either of

  • Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
  • MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.





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