#wasmer #web-assembly #publish #registry

bin+lib cargo-wasmer

Publish a Rust crate to the WebAssembly Package Manager

2 unstable releases

0.4.0 Oct 26, 2023
0.3.6 Oct 26, 2023

#218 in Cargo plugins

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Cargo Wasmer

Continuous Integration

(API Docs)

A cargo sub-command for publishing Rust crates to the Wasmer package registry.

If you want a deeper understanding of how cargo wasmer works, check out Announcing Cargo WAPM.

Note: This command used to be called cargo wapm back when wapm was a separate command. Most interactions with the Wasmer registry have been merged into the wasmer CLI nowadays, so the command was renamed to cargo wasmer.

Getting Started

You can install the cargo wasmer command from crates.io.

$ cargo install cargo-wasmer --locked

You will also need to install the wasmer CLI and authenticate with the registry.

$ curl https://get.wasmer.io -sSfL | sh
$ wasmer login
Username: my-user
Password: ****

Once you have done that, open the Cargo.toml for your crate and add a metadata section to tell cargo wasmer how your crate will be packaged.

# Cargo.toml
namespace = "Michael-F-Bryan"
abi = "none"

The abi argument tells cargo wasmer which target to use when compiling to WebAssembly.

ABI Target Triple
none wasm32-unknown-unknown
wasi wasm32-wasi
emscripten wasm32-emscripten

You also need to add cdylib to the crate-type list. You should also add the rlib crate type if other crates depend on this crate (integration tests, doc tests, examples, etc.).

# Cargo.toml
crate-type = ["cdylib", "rlib"]

Now the Cargo.toml is up to date, we can do a dry run to make sure everything is correct.

$ cd examples/hello-world/
$ cargo wasmer --dry-run
2022-05-03T17:33:31.929353Z  INFO publish: cargo_wasmer: Publishing dry_run=true pkg="hello-world"
Successfully published package `Michael-F-Bryan/hello-world@0.1.0`
[INFO] Publish succeeded, but package was not published because it was run in dry-run mode
2022-05-03T17:33:32.366576Z  INFO publish: cargo_wasmer: Published! pkg="hello-world"

We can see that some files have been written to the target/wasmer/ folder.

$ tree ../../target/wasmer
└── hello-world
    ├── hello_world.wasm
    ├── LICENSE_MIT.md
    ├── README.md
    └── wasmer.toml

1 directory, 4 files

$ cat ../../target/wasmer/hello-world/wasmer.toml
name = "Michael-F-Bryan/hello-world"
version = "0.1.0"
description = "A dummy package."
license-file = "LICENSE_MIT.md"
readme = "README.md"

name = "hello-world"
source = "hello_world.wasm"
abi = "none"

If you are happy with the generated files, remove the --dry-run command to publish the crate for real.

The cargo wasmer command doesn't take care of any version bumping, so the version being published is read directly from Cargo.toml. Check out the cargo release tool if you something that can manage routine release tasks like bumping versions, tagging commits, or updating your changelog.


Normally, the cargo wasmer command will only publish the crate in the current directory.

However, by using the --workspace flag you can publish every crate in the current workspace as long as they have a [package.metadata.wasmer] section in their Cargo.toml. The --exclude argument lets you skip a particular crate while publishing.


This repository uses Release Please to automate a lot of the work around creating releases.

Every time a commit following the Conventional Commit Style is merged into main, the release-please.yml workflow will run and update the "Release PR" to reflect the new changes.

For commits that just fix bugs (i.e. the message starts with "fix: "), the associated crate will receive a changelog entry and a patch version bump. Similarly, adding a new feature (i.e. "feat:") does a minor version bump and adding breaking changes (i.e. "fix!:" or "feat!:") will result in a major version bump.

When the release PR is merged, the updated changelogs and bumped version numbers will be merged into the main branch, the release-please.yml workflow will automatically generate GitHub Releases, and CI will publish the crate if necessary.


  1. Use Conventional Commit Messages whenever you make a noteworthy change
  2. Merge the release PR when ready to release
  3. Let the automation do everything else


This project is licensed under the Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0).

It is recommended to always use cargo-crev to verify the trustworthiness of each of your dependencies, including this one.


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.

The intent of this crate is to be free of soundness bugs. The developers will do their best to avoid them, and welcome help in analysing and fixing them.


~194K SLoC