How does Cargo interpret a version like "1.0"?

By default a bare version string is a caret requirement, so 1.0 means at least 1.0.0 but below 2.0.0. Cargo picks the newest compatible release and records the exact choice in Cargo.lock. Use an explicit operator like =1.0.3 only when you need to freeze a single version.

What is the difference between dependencies and dev-dependencies?

dependencies are compiled into your crate and ship to users. dev-dependencies are only used for tests, examples and benchmarks and are not built when someone depends on your crate, so test frameworks like criterion belong there to keep the public dependency tree small.

When should I pick lib versus bin?

Choose bin for an application that produces an executable from src/main.rs. Choose lib for a reusable crate built from src/lib.rs that other crates depend on. A crate can also be both, but the tool emits the single target you select to keep the manifest simple.

What does the edition field control?

The edition selects a stable set of language semantics, such as 2021 or 2024. Editions let Rust evolve syntax and idioms without breaking older code, since each crate opts into its own edition. New projects should use the latest edition the compiler supports.

Why enable LTO and codegen-units in the release profile?

Link-time optimization (lto = true) and codegen-units = 1 let the compiler optimize across the whole program in one unit, producing faster, smaller release binaries at the cost of longer compile times. They only affect release builds, so debug builds stay fast.

Cargo.toml Builder (Rust)

Email me this result

Get this tool's output sent to your inbox, plus one useful tool a week. No spam, unsubscribe any time.

The Cargo.toml Builder generates the manifest at the heart of every Rust project. Choose whether you are building a binary or a library, pick the crates you need, and the tool emits a complete [package], [dependencies], [dev-dependencies] and release profile.

How it works

[package] holds the crate name, version, edition, authors and license. The target section is either [[bin]] (an executable from src/main.rs) or [lib] (a reusable library from src/lib.rs). [dependencies] lists each crate you selected, using Cargo’s table syntax when features are needed — for example serde is emitted as serde = { version = "1.0", features = ["derive"] } so the derive macros are enabled.

Cargo treats a bare version string as a caret requirement: "1.0" resolves to any 1.x release at or above 1.0.0. The exact versions Cargo actually selects are written to Cargo.lock on first build, which is what makes builds reproducible.

Example

After saving the manifest, build to lock dependencies:

cargo build           # resolves versions, writes Cargo.lock
cargo build --release # optimized build using [profile.release]

Tips and notes

Keep test-only crates such as criterion and tokio-test in [dev-dependencies] so consumers of your library never compile them. Commit Cargo.lock for binaries to pin exact versions; for libraries it is conventional to leave it out so downstream projects resolve their own tree. The release profile enables lto and codegen-units = 1 for faster, smaller binaries — these only affect --release builds, so day-to-day debug compiles stay quick.