🩸 Ferretin

A terminal-based Rust documentation viewer

Ferretin reads rustdoc JSON output to display Rust documentation directly in your terminal. It supports local workspace crates, standard library documentation, and crates from crates.io, with search functionality and modern terminal features including mouse support, syntax highlighting, and clickable links.

Features

• Interactive documentation browser with keyboard and mouse navigation
• One-shot CLI for quick documentation lookups in the terminal
• Search across crates or within specific crates
• Works seamlessly across three contexts:
  • Local workspace crates (requires nightly toolchain)
  • Standard library (requires rust-docs-json rustup component)
  • Crates from crates.io (fetched from docs.rs on demand)
• Modern terminal UI with features like italics, unicode box drawing, syntax highlighting, OSC8 hyperlinks, cursor changes in terminals that support it, and mouse hover previews
• Fast navigation with history and breadcrumb trail

Installation

cargo install ferretin

Optional: Standard library documentation

To view documentation for std, core, and alloc:

rustup component add rust-docs-json

For local workspace documentation

Local crate documentation requires a nightly toolchain:

rustup toolchain install nightly

Note: There is a relationship between ferretin's version and the nightly toolchain version. Ferretin currently supports rustdoc JSON format versions 55, 56, and 57. If your nightly generates a newer format, ferretin won't be able to build local documentation until support is added.

Usage

Interactive mode

Launch the interactive browser:

ferretin -i

Once running, use h or ? to see available keybindings. Basic navigation:

• g - go to an item by path (e.g., std::vec::Vec)
• s - search (Tab to toggle between current crate and all crates)
• l - list available crates
• Arrow keys, j/k, or mouse to navigate
• Click on links to follow them

CLI mode

View documentation for a specific item:

ferretin get std::vec::Vec
ferretin get serde::Serialize

Search for items:

ferretin search "hash map"
ferretin search --crate tokio "spawn"

List available crates in your workspace:

ferretin list

Caching and Storage

Ferretin caches documentation JSON files to avoid repeated downloads and builds:

• Crates.io documentation: Cached in $CARGO_HOME/rustdoc-json/{format-version}/{crate_name}/{crate_version}.json
• Search indices: Binary .index files are generated lazily on first search and stored alongside JSON files
• Standard library search indices: Written to {rustc sysroot}/share/doc/rust/json/ if available

The cache uses cargo's home directory (typically ~/.cargo on Unix systems).

Current Status

Ferretin is at version 0.1 and actively used by the author as a primary documentation interface. It's ready for general use, though the output format should be considered unstable and may change between versions.

If you're scripting against ferretin's output, be aware that the text format may change. Pin to a specific version or be prepared to update your scripts.

Platform Support

Ferretin is developed and tested on Unix-like systems. Windows compatibility is untested. If you encounter issues on Windows or other platforms, please open an issue or pull request.

Related Projects

Ferretin was originally developed to support the rustdoc-mcp MCP server, which provides Rust documentation access for Claude Code and other MCP clients.

License