Map Rust source into a module tree

About this tool

Rust crates grow a hierarchy quickly: mod declarations, nested modules, public and private types, traits, impl blocks, methods, tests, and constants all compete for attention. This tool turns pasted Rust source into a compact map of that hierarchy so you can understand a module before editing it, paste a quick graph into an issue, or export a machine-readable outline.

The parser is syn, not a brace-counting regex. That means inline modules, external mod foo; declarations, visibility such as pub(crate), impl methods, trait declarations, #[cfg(test)], and #[test] attributes are read from Rust syntax. For multi-file snippets, separate files with headers:

=== src/lib.rs ===
pub mod util;

=== src/util.rs ===
pub fn slug() {}

Worked example

Input:

pub mod config {
    pub struct Config;
    impl Config { pub fn load() -> Self { Config } }
}

pub trait Service { fn run(&self); }
fn main() {}

Default tree output:

crate
├── mod config: pub
│   ├── struct Config: pub
│   └── impl Config
│       └── fn load: pub
├── trait Service: pub
└── fn main: pub(self)

Switch to Mermaid when you want a pasteable graph, JSON when another script needs counts and children, or paths when you want a grep-friendly list like crate::config::Config::load (fn, pub).

Practical uses

• Review a copied lib.rs or module before making a change.
• Compare the public/private shape of a file before and after refactoring.
• Include #[cfg(test)] modules only when you need test helpers in the map.
• Focus on one subtree with focus_on=crate::module.
• Hide function nodes or type nodes to make a high-level diagram fit in a pull request comment.

Limits and edge cases

• Input is capped at 512 KiB and module nesting at 64 levels.
• This maps the text you paste. It does not run cargo metadata, load files from disk, expand macros, resolve feature flags, or follow #[path] attributes.
• A mod foo; declaration is marked (external) unless a matching === src/foo.rs === or === src/foo/mod.rs === section is pasted too.
• include_tests is off by default, matching the usual source map view. Turn it on for #[cfg(test)] modules and #[test] functions.
• Mermaid output is plain text; paste it into Markdown or a Mermaid renderer to see the graph.

FAQ