What is Cargo.toml

Cargo.toml is the manifest and configuration file for a Rust project. It acts as a project's control center, defining its name, version, and external libraries(dependencies). Example Cargo.toml:

[package]
name = "linked_list"        // name of program
version = "0.1.0"           // current version
edition = "2024"            //  Rust edition in your code

// Lists the external libraries (crates) needed by project
// Cargo automatically fetches these packages from crates.io and compiles them
[dependencies]
serde = { version = "1.0", features = ["derive"] }
reqwest = "0.12"

[dev-dependencies]          // Libraries required only for running tests

[build-dependencies]    // Crates required for your build scripts (e.g., build.rs)

[features]  // compile-time flags to enable conditional compilation

// section to manage different crates from 1 location
[workspace]
      

Sections on Cargo.toml

workspace

[workspace]: header in root Cargo.toml, we define that directory as the "root" of a multi-crate project.
[members]: which subdirectories contain the crates that belong to this workspace. When you run a command like cargo build from the root, Cargo looks at these members and builds them together
resolver = "2": This is Feature Resolver version. This came in Rust 2021. It fixed feature bloat issues in Rust
{ workspace = true }: Workspace inheritance. Don't look for a version number here. Go to the root Cargo.toml, find the tokio version and features are defined there.

Project Structure
 |- Cargo.toml      //main
 |- crates
        |- module1
            |- Cargo.toml
            |- src/main.rs
        |- module2
            |- Cargo.toml
            |- src
                |- module21
                |- main.rs
      

Cargo.toml
[workspace]
resolver = "2"
members = [
    "crates/module1",
    "crates/module1"
]

# ── Project-wide dependency versions (single source of truth) ─────
[workspace.dependencies]
tokio       = { version = "1",    features = ["full"] }
tokio-util  = { version = "0.7",  features = ["rt"] }
...

# ── Internal crate cross-references ──
module1 = { path = "crates/module1 }
module2 = { path = "crates/module2" }
      

module1/Cargo.toml
[package]
name        = "module1"
version     = "0.1.0"
edition     = "2021"
description = ".."

[[bin]]
name = "module1"
path = "src/main.rs"

# ── Workspace Inheritance ─────
[dependencies]
module2      = { workspace = true }

tokio         = { workspace = true }
tokio-util    = { workspace = true }
..