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Ferritin — Rust documentation MCP Server

rs.ferritin/rustdoc

Search and read Rust documentation for the standard library and any crate on crates.io

What is the Ferritin — Rust documentation MCP server?

The Ferritin MCP server provides access to Rust documentation through an interactive browser and CLI interface. It supports searching and retrieving documentation from the standard library, local workspace crates, and crates from crates.io, with features like syntax highlighting, search functionality, and fast navigation.

Ferritin reads rustdoc JSON output to display Rust documentation directly in your terminal or through MCP. It works seamlessly across local workspace crates (with nightly), the standard library (with rust-docs-json component), and crates from crates.io (fetched from docs.rs on demand). Use it to quickly look up API documentation, search across crates, and navigate Rust code references without leaving your editor.

How to install Ferritin — Rust documentation

Copy-paste configuration for popular MCP clients.

transport: http

Config generated by PluginBench — verify against the source before use.

~/.cursor/mcp.json

{
  "mcpServers": {
    "rustdoc": {
      "url": "https://ferritin.rs/mcp"
    }
  }
}

Tools & capabilities

Tools this server exposes to the agent.

get — Retrieve documentation for a specific item by path (e.g., std::vec::Vec)
search — Search for items across all crates or within a specific crate
list — List available crates in your workspace

Use cases

Look up standard library documentation (std, core, alloc) while coding
Search for specific functions or types across crates.io
Browse API documentation for dependencies in your project
Retrieve documentation for local workspace crates
Get structured JSON output of documentation for programmatic use

Ferritin — Rust documentation MCP server FAQ

What is Ferritin?

Ferritin is a Rust documentation viewer that reads rustdoc JSON output and displays documentation in your terminal or through MCP. It supports the standard library, local workspace crates, and any crate from crates.io.

Is Ferritin free?

Yes, Ferritin is open source and free to use, licensed under Apache 2.0 or MIT.

How do I install Ferritin for use with Claude or Cursor?

Use the remote MCP endpoint at https://ferritin.rs/mcp in your MCP configuration. For local installation, use cargo install ferritin or cargo binstall ferritin.

What setup is required to view standard library documentation?

Install the rust-docs-json rustup component with: rustup component add rust-docs-json

Can I search documentation for local workspace crates?

Yes, but it requires a nightly Rust toolchain. Install with: rustup toolchain install nightly

What output formats does Ferritin support?

Ferritin supports ANSI colors for terminals, plain text when piped, markdown-flavored format for coding agents, and JSON for programmatic use via --format flag.

README (reference)

Source of truth, from the repository.

🩸 Ferritin

A terminal-based Rust documentation viewer

Ferritin 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

Prebuilt binary (recommended)

Prebuilt binaries skip compilation and are available for x86_64/aarch64 macOS, x86_64 Linux, and x86_64 Windows.

If you have cargo-binstall, it reads the release metadata and installs the right binary for your platform:

cargo binstall ferritin

Otherwise, the installer scripts detect your platform, download the matching binary, and place it in ~/.cargo/bin:

macOS and Linux:

curl --proto '=https' --tlsv1.2 -LsSf https://github.com/jbr/ferritin/releases/download/ferritin-latest/ferritin-installer.sh | sh

Windows (PowerShell):

powershell -c "irm https://github.com/jbr/ferritin/releases/download/ferritin-latest/ferritin-installer.ps1 | iex"

Both of the above always install the most recent release. You can also pick a specific version or download archives directly from the releases page.

From source

To build from source (or for a platform without a prebuilt binary):

cargo install ferritin

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 ferritin's version and the nightly toolchain version. Ferritin supports a range of recent rustdoc JSON format versions, and if your nightly generates a newer format, ferritin will make a best effort at parsing it.

Usage

Interactive mode

Launch the interactive browser:

ferritin -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:

ferritin get std::vec::Vec
ferritin get serde::Serialize

Search for items:

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

List available crates in your workspace:

ferritin list

Output format

Ferritin auto-detects how to render: ANSI colors on a terminal, plain text when piped, and a compact markdown-flavored format under a coding agent. Override it with --format <tty|plain|agent|json>. --format json emits a structured representation — of the resolved item for get, or of the results for search/list — for scripting and programmatic consumers:

ferritin get std::vec::Vec --format json

(The JSON shape is still settling as the library API evolves; a published JSON Schema is planned.)

Caching and Storage

Ferritin keeps its caches under a single directory — $FERRITIN_HOME if set, else $XDG_CACHE_HOME/ferritin, else ~/.cache/ferritin. Everything in it is reconstructible (fetched or derived), so it is always safe to delete:

Crates.io documentation: raw rustdoc JSON at docs/{crate}/{version}/{format-version}.json, with derived binary caches beside it (an rkyv archive for fast partial loads, and a .index file generated lazily on first search)
crates.io metadata: the crate-names artifacts (crate-names/) used for version resolution and typeahead, and per-crate version lookups (crates-io-versions/)
Standard library search indices: written to {rustc sysroot}/share/doc/rust/json/ if available
Local workspace documentation: built into the workspace's own target/doc/, not the shared cache

Earlier versions cached under $CARGO_HOME/rustdoc-json; a cache found there is migrated automatically on first run.

Environment Variables

Variable	Meaning
`FERRITIN_HOME`	Cache root override (see above)
`FERRITIN_THEME`	Default color theme (equivalent to `--theme`)
`FERRITIN_CRATE_NAMES_URL`, `FERRITIN_CRATE_DESCRIPTIONS_URL`	Override where the crate-names artifacts are fetched from (e.g. a mirror)

ferritin serve (the opt-in serve/acme features; not present in distributed binaries) is configured 12-factor style:

Variable	Meaning
`HOST`, `PORT`	Bind address (`::` binds dual-stack)
`FERRITIN_CACHE_BYTES`	In-memory crate-cache weight cap
`FERRITIN_RSS_HIGH_WATER_BYTES`	RSS guard threshold (Linux only): shed cache weight when anonymous RSS exceeds it
`FERRITIN_RATELIMIT`	Per-client `/api` requests per minute
`FERRITIN_ACME_DOMAIN`	Activates automatic HTTPS via Let's Encrypt for this domain
`FERRITIN_ACME_CACHE_DIR`	Required with ACME: persists the account key and certificates
`FERRITIN_ACME_CONTACT`	Optional ACME contact email
`FERRITIN_ACME_PRODUCTION`	Use the Let's Encrypt production directory (default: staging)

Development-only knobs (not part of the stable interface): FERRITIN_TEST_MODE (normalized snapshot-test output), FERRITIN_REINDEX (rebuild search indexes in memory, bypassing the disk cache), and the search-scoring probes FERRITIN_NAME_WEIGHT, FERRITIN_ANCESTOR_WEIGHTS, and FERRITIN_NAME_PREFIX_COUNT.

Current Status

Ferritin is at version 0.x 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 ferritin's output, be aware that the text format may change. Pin to a specific version or be prepared to update your scripts.

Platform Support

Ferritin is developed primarily on Unix-like systems and is also tested on Windows, where both the CLI and interactive TUI work (prebuilt x86_64 Windows binaries are provided). If you encounter issues on any platform, please open an issue or pull request.

Related Projects

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

License

<sup> Licensed under either of <a href="LICENSE-APACHE">Apache License, Version 2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option. </sup>

<sub> Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions. </sub>