Cargo.toml (Rust) to JSON Conversion

Cargo.toml is the manifest file for Rust projects, managed by the Cargo package manager. It is one of the most well-known real-world uses of TOML. Understanding its JSON equivalent is useful for tooling, CI pipelines, and programmatic dependency management.

A typical Cargo.toml:

[package]
name = "my-app"
version = "0.1.0"
edition = "2021"
authors = ["Alice <alice@example.com>"]
description = "A sample Rust application"

[dependencies]
serde = { version = "1.0", features = ["derive"] }
tokio = { version = "1", features = ["full"] }
reqwest = "0.11"

[dev-dependencies]
criterion = "0.5"

[features]
default = ["logging"]
logging = ["serde/std"]

[[bin]]
name = "my-app"
path = "src/main.rs"

Converts to JSON:

{
  "package": {
    "name": "my-app",
    "version": "0.1.0",
    "edition": "2021",
    "authors": ["Alice <alice@example.com>"],
    "description": "A sample Rust application"
  },
  "dependencies": {
    "serde": {"version": "1.0", "features": ["derive"]},
    "tokio": {"version": "1", "features": ["full"]},
    "reqwest": "0.11"
  },
  "dev-dependencies": {
    "criterion": "0.5"
  },
  "features": {
    "default": ["logging"],
    "logging": ["serde/std"]
  },
  "bin": [
    {
      "name": "my-app",
      "path": "src/main.rs"
    }
  ]
}

Notable conversion details:

• Dependencies can be either a simple string ("0.11") or an inline table with version and features. Both forms are valid TOML and produce different JSON structures.
• [[bin]] uses the array of tables syntax, creating a JSON array of objects under the bin key.
• Features are arrays of strings referencing other features or dependency features ("serde/std").
• Hyphenated keys like dev-dependencies are valid bare keys in TOML and become regular JSON string keys.

Cargo reads only TOML, but the JSON representation is used by cargo metadata, crate registries (crates.io API), and build tools that analyze dependency graphs programmatically.