What Is Cargo.toml vs Cargo.lock

Use Cargo.toml to define your project's dependencies and settings, and let Cargo.lock automatically record the exact versions resolved for reproducible builds. You edit Cargo.toml to add or change dependencies, while Cargo.lock is generated by Cargo and should be committed to version control to ensure everyone builds with the same dependency tree.

[package]
name = "your-project"
version = "0.1.0"
edition = "2024"

[dependencies]
serde = "1.0"

cargo build

Cargo.lock is created automatically after the first build and contains the precise versions of all dependencies and their transitive dependencies.

Cargo.toml is your project's recipe book where you list what ingredients (dependencies) you need. Cargo.lock is the exact shopping list generated from that recipe, ensuring you always buy the same specific items every time. You write the recipe, but you trust the system to lock down the exact items so your project builds the same way for everyone.