Cargo — Rust's Package Manager & Build Tool

Cargo is npm + tsc + jest in one

If you have used npm (or yarn/pnpm), Cargo will feel immediately familiar. It manages dependencies, builds your project, runs your code, and runs your tests — all under one roof.

Creating a new project

# Node / TypeScript
mkdir my-app && cd my-app
npm init -y
npm install typescript --save-dev

# Rust
cargo new my-app   # creates a binary (has fn main)
cargo new my-lib --lib   # creates a library (no fn main)
cd my-app

cargo new creates:

flowchart TD
  root["my-app/"] --> toml["Cargo.toml — like package.json"]
  root --> lock["Cargo.lock — like package-lock.json"]
  root --> src["src/"]
  src --> main["main.rs — entry point"]

What cargo new creates

Cargo.toml vs package.json

TypeScript

// package.json
{
  "name": "my-app",
  "version": "1.0.0",
  "dependencies": {
    "express": "^4.18.0"
  },
  "devDependencies": {
    "typescript": "^5.0.0",
    "@types/express": "^4.17.0"
  }
}

Rust

# Cargo.toml
[package]
name = "my-app"
version = "0.1.0"
edition = "2021"

[dependencies]
axum = "0.7"
tokio = { version = "1", features = ["full"] }
serde = { version = "1", features = ["derive"] }

[dev-dependencies]
# test-only crates go here

Adding dependencies

# npm
npm install serde_json        # runtime dep
npm install --save-dev vitest # dev dep

# Cargo
cargo add serde_json          # runtime dep
cargo add --dev pretty_assertions  # dev dep

cargo add updates Cargo.toml automatically, exactly like npm install.

Core subcommands

cargo build          # compile (debug, fast, unoptimized)
cargo build --release  # compile (optimized, slower build)
cargo run            # compile + execute
cargo run -- --port 8080  # pass args to your binary
cargo check          # type-check only, no binary (very fast)
cargo test           # run all tests
cargo test my_fn     # run tests whose name contains "my_fn"
cargo doc --open     # generate + open HTML docs
cargo clean          # delete target/ directory

Cargo.lock — commit it or not?

# Binary / application  →  COMMIT Cargo.lock (reproducible builds)
# Library crate         →  DO NOT commit Cargo.lock (let consumers pick versions)

This mirrors npm’s convention: applications commit package-lock.json; published libraries typically do not.

🟦 edition = 2021

Rust releases a new edition every three years (2015, 2018, 2021). An edition may introduce breaking syntax changes, but the compiler can migrate your code automatically with cargo fix --edition. Always use edition = "2021" for new projects — it enables let-else, the prelude improvements, and better closure captures.

Which command adds a crate to your project (equivalent to `npm install <pkg>`)?

cargo install cargo fetch cargo add cargo get

What does `cargo check` do differently from `cargo build`?

It only runs tests It type-checks and reports errors without producing a binary It checks for outdated dependencies It validates Cargo.toml syntax only

Should you commit Cargo.lock for a binary application?

No — it is auto-generated and should be ignored Yes — it ensures reproducible builds across machines Only on CI, never locally Only when using workspaces

Which file in Cargo is most similar to package.json?

Cargo.lock src/main.rs Cargo.toml .cargo/config.toml

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